tag:theconversation.com,2011:/uk/topics/stars-1145/articlesStars – The Conversation2024-03-22T14:32:05Ztag:theconversation.com,2011:article/2263612024-03-22T14:32:05Z2024-03-22T14:32:05ZStellar murder: when stars destroy and eat their own planets<figure><img src="https://images.theconversation.com/files/583649/original/file-20240322-22-txhykg.jpg?ixlib=rb-1.1.0&rect=3%2C0%2C1036%2C584&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/missions/chandra/nasas-chandra-planets-can-be-anti-aging-formula-for-stars/">NASA/CXC/M.Weiss</a></span></figcaption></figure><p>Our Sun is both our best friend and our worst enemy. On the one hand, we owe our very existence to our star. Earth and the other planets in the Solar System formed out of the same cloud of gas and dust as the Sun. </p>
<p>And without its light, there could be no life on this planet. On the other hand, there will come a day when the Sun ends all life on Earth and, eventually, destroys Earth itself.</p>
<p>The risks that stars can pose to their planets are highlighted by <a href="https://www.nature.com/articles/d41586-024-00847-6">a new study published in Nature</a>. The authors looked at stars similar to our Sun and found that at least one in 12 stars exhibits traces of metals in its atmosphere. These are thought to be the scars of planets and asteroids that have been ingested by the stars. </p>
<p>Planets should never feel too comfortable as they orbit their parent star, as there are at least two ways in which their star can betray their trust and bring about their violent demise. </p>
<h2>Tidal disruption</h2>
<p>The first is through a process called “tidal disruption”. As a planetary system forms, some planets will find themselves orbiting their star along paths that are either not quite circular or are slightly inclined relative to the plane of the star’s rotation. When that happens, the gravitational force exerted by the star on the planet will slowly correct the shape or the alignment of the wayward planet’s orbit. </p>
<p>In extreme cases, the gravitational force applied by the star will destabilise the planet’s orbit, slowly pulling it closer and closer. If the hapless planet strays too close, it will be torn apart by the star’s gravity. This happens because the side of the planet facing the star is slightly closer than the side facing away (the difference is the planet’s diameter). </p>
<p>The strength of the gravitational pull exerted by the star depends on the distance between it and the planet, so that the side of the planet facing the star feels a slightly stronger pull than the side facing away. </p>
<p>On Earth, this difference in the strength of the force of gravity creates the daily ebb and flow of the tides. In essence, the Sun is trying to deform Earth, but is far enough away that it only manages to pull on the waters of its oceans. But a planet dangerously close to its star will find its very crust and core being pulled apart by these tides. </p>
<p>If the planet is not too close to the star, its shape will merely be deformed into that of an egg. Just a little closer to the star, and the difference between the gravitational pull on its different sides will be enough to completely tear it apart, reducing it back to a cloud of gas and dust that spirals into the star and vaporises in its hellish fires.</p>
<p>The process of tidal disruption was first suggested some 50 years ago. For the last couple of decades, astronomers — including my group — have observed dozens of bright tidal disruption flares caused by <a href="https://science.nasa.gov/resource/tidal-disruption-event/">stars shredded by supermassive black holes</a> in the centres of galaxies. </p>
<figure class="align-center ">
<img alt="Planet and binary star." src="https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583650/original/file-20240322-26-mpjqcm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The new study in Nature looked specifically at stars orbiting each other in binary systems.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details/PIA21470">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>Last year, for the first time, a group of astronomers reported observing a similar, dimmer flare that was consistent with <a href="https://www.nasa.gov/missions/neowise/caught-in-the-act-astronomers-detect-a-star-devouring-a-planet/">a planet being disrupted and consumed by its star</a>. </p>
<p>Tidal disruption of planets may be quite common, as shown by the new finding that at least 1 in 12 stars exhibits signs that <a href="https://www.nature.com/articles/d41586-024-00847-6">they have ingested planetary material</a>. </p>
<p>Other studies have found that between a quarter to half of all white dwarfs – the remnants of stars up to twice as massive as our Sun – sport similar scars. As their name implies, white dwarfs are white hot. With surface temperatures of tens of thousands of degrees, the hottest white dwarfs emit ultraviolet and X-ray light energetic enough to <a href="https://www.syfy.com/syfy-wire/a-dead-star-is-vaporizing-its-planets">vaporise their orbiting planets</a>.</p>
<h2>The end of Earth</h2>
<p>Rest assured; Earth won’t be destroyed via tidal disruption. Our planet’s end will come in about five billion years, when the Sun will transition into a red giant. </p>
<p>Stars are powered by <a href="https://www.energy.gov/science/doe-explainsnuclear-fusion-reactions#:%7E:text=Nuclear%20Fusion%20reactions%20power%20the,The%20leftover%20mass%20becomes%20energy.">the process known as fusion</a>, where two light elements are combined to make a heavier one. All stars start out their lives fusing the element hydrogen in their cores into the element helium. This fusion process both stabilises them against implosion, due to the incessant pull of gravity, and creates the light that makes them shine. Our Sun has been fusing hydrogen into helium for roughly 4.5 billion years. </p>
<p>But 4.5 billion years from now, the hydrogen in the Sun’s core will run out. All fusion in the core will stop, and gravity, unopposed, will force the star to contract. As the core contracts, it will heat up until the temperature is high enough for helium to fuse into carbon. </p>
<p>Fusion will once again stabilise the star. In the meantime, though, the outer envelopes of the star will expand and cool, giving the now giant star a redder hue. As the red giant Sun expands, it will <a href="https://www.scientificamerican.com/article/the-sun-will-eventually-engulf-earth-maybe/">engulf Mercury, Venus and Earth</a> – it may even reach all the way out to the orbit of Mars. </p>
<p>Earth may have another five billion years to go, but we will not be here to witness its extinction. As the Sun burns through its hydrogen stores, it steadily grows brighter: every billion years, its luminosity increases by about 10%. </p>
<p>A billion years from now, the Sun will be bright enough to <a href="https://theconversation.com/the-sun-wont-die-for-5-billion-years-so-why-do-humans-have-only-1-billion-years-left-on-earth-37379">boil away Earth’s oceans</a>. So, the next time you bask in the warm rays of the Sun, remember: it’s got it in for us.</p><img src="https://counter.theconversation.com/content/226361/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Or Graur receives funding from UKRI Science and Technology Facilities Council.. </span></em></p>There are several ways in which stars can destroy and swallow their own planets.Or Graur, Associate Professor of Astrophysics, University of PortsmouthLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2262622024-03-21T18:01:43Z2024-03-21T18:01:43Z‘Dark stars’: dark matter may form exploding stars – and observing the damage could help reveal what it’s made of<figure><img src="https://images.theconversation.com/files/583424/original/file-20240321-23-mbtrm1.jpeg?ixlib=rb-1.1.0&rect=0%2C262%2C1280%2C597&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">We wouldn't be able to see them directly, but they could be out there.</span> <span class="attribution"><a class="source" href="https://esawebb.org/images/potm2301a/">ESA/Webb, NASA & CSA, A. Martel</a></span></figcaption></figure><p>Dark matter is a ghostly substance that astronomers have failed to detect for decades, yet which we know has an enormous influence on normal matter in the universe, such as stars and galaxies. Through the massive gravitational pull it exerts on galaxies, it spins them up, gives them an extra push along their orbits, or even rips them apart. </p>
<p>Like a cosmic carnival mirror, it also bends the light from distant objects to create distorted or multiple images, a process which is called <a href="https://theconversation.com/uk/topics/gravitational-lensing-112201">gravitational lensing</a>. </p>
<p>And <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.109.043018">recent research</a> suggests it may create even more drama than this, by producing stars that explode.</p>
<p>For all the havoc it plays with galaxies, not much is known about whether dark matter can interact with itself, other than through gravity. If it experiences other forces, they must be very weak, otherwise they would have been measured.</p>
<p>A possible candidate for a dark matter particle, made up of a hypothetical class of weakly interacting massive particles (or <a href="https://www.symmetrymagazine.org/article/july-2015/miraculous-wimps?language_content_entity=und">WIMPs</a>), has been studied intensely, so far with no observational evidence.</p>
<p>Recently, other types of particles, also weakly interacting but extremely light, have become the focus of attention. These particles, called <a href="https://bigthink.com/starts-with-a-bang/axions-dark-matter/">axions</a>, were first <a href="https://www.symmetrymagazine.org/article/the-other-dark-matter-candidate?language_content_entity=und">proposed in late 1970s</a> to <a href="https://www.forbes.com/sites/startswithabang/2019/11/19/the-strong-cp-problem-is-the-most-underrated-puzzle-in-all-of-physics/">solve a quantum problem</a>, but they may also fit the bill for dark matter. </p>
<p>Unlike WIMPs, which cannot “stick” together to form small objects, axions can do so. Because they are so light, a huge number of axions would have to account for all the dark matter, which means they would have to be crammed together. But because they are a type of subatomic particle known as a <a href="https://www.science.org/doi/10.1126/sciadv.abj3618">boson</a>, they don’t mind.</p>
<p>In fact, calculations show axions could be packed so closely that they start behaving strangely – collectively acting like a wave – according to the rules of quantum mechanics, the theory which governs the microworld of atoms and particles. This state is called a <a href="https://www.pbs.org/wgbh/nova/article/ultracold-atoms/">Bose-Einstein condensate</a>, and it may, unexpectedly, <a href="https://www.livescience.com/63977-axion-stars-form-quickly.html">allow axions to form “stars”</a> of their own. </p>
<p>This would happen when the wave moves on its own, forming what physicists call a “soliton”, which is a localised lump of energy that can move without being distorted or dispersed. This is often seen on Earth in vortexes and whirlpools, or the bubble rings that <a href="https://thekidshouldseethis.com/post/what-will-dolphins-make-of-these-underwater-bubble-rings">dolphins enjoy underwater</a>.</p>
<p>The <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.109.043018">new study</a> provides calculations which show that such solitons would end up growing in size, becoming a star, similar in size to, or larger than, a normal star. But finally, they become unstable and explode. </p>
<p>The energy released from one such explosion (dubbed a “bosenova”) would rival that of a supernova (an exploding normal star). Given that dark matter far outweighs the visible matter in the universe, this would surely leave a sign in our observations of the sky. We have yet to find such scars, but the new study gives us something to look for.</p>
<h2>An observational test</h2>
<p>The <a href="https://phys.org/news/2024-02-explosive-axion-stars-dark.html">researchers behind the study</a> say that the surrounding gas, made of normal matter, would absorb this extra energy from the explosion and emit some of it back. Since most of this gas is made of hydrogen, we know this light should be in radio frequencies. </p>
<p>Excitingly, future observations with the <a href="https://theconversation.com/in-australia-and-south-africa-construction-has-started-on-the-biggest-radio-observatory-in-earths-history-195818">Square Kilometre Array</a> radio telescope may be able to pick it up.</p>
<figure class="align-center ">
<img alt="Artist's impression of the SKA telescope." src="https://images.theconversation.com/files/583420/original/file-20240321-20-b3sckt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583420/original/file-20240321-20-b3sckt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583420/original/file-20240321-20-b3sckt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583420/original/file-20240321-20-b3sckt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583420/original/file-20240321-20-b3sckt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583420/original/file-20240321-20-b3sckt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583420/original/file-20240321-20-b3sckt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of the SKA telescope.</span>
<span class="attribution"><span class="source">wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>So, while the fireworks from dark star explosions may be hidden from our view, we might be able to find their aftermath in the visible matter. What’s great about this is that such a discovery would help us work out what dark matter is actually made of – in this case, most likely axions.</p>
<p>What if observations will not detect the predicted signal? That probably won’t rule out this theory completely, as other “axion-like” particles are still possible. A failure of detection may indicate, however, that the masses of these particles are very different, or that they do not couple with radiation as strongly as we thought.</p>
<p>In fact, this has happened before. Originally, it was thought that axions would couple so strongly that they would be able to <a href="https://www.youtube.com/watch?v=3EjezghXkaw">cool the gas inside stars</a>. But since models of star cooling showed stars were just fine without this mechanism, the axion coupling strength had to be lower than originally assumed.</p>
<p>Of course, there is no guarantee that dark matter is made of axions. WIMPs are still contenders in this race, and <a href="https://theconversation.com/from-machos-to-wimps-meet-the-top-five-candidates-for-dark-matter-51516">there are others too</a>. </p>
<p>Incidentally, some studies suggest that WIMP-like dark matter <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.100.051101">may also form “dark stars”</a>. In this case, the stars would still be normal (made of hydrogen and helium), with dark matter just powering them. </p>
<p>These WIMP-powered dark stars are predicted to be supermassive and to live only for a short time in the early universe. But they could be observed by the James Webb space telescope. A recent study has claimed <a href="https://www.scientificamerican.com/article/jwst-might-have-spotted-the-first-dark-matter-stars/">three such discoveries</a>, although the jury is still out on whether that’s really the case.</p>
<p>Nevertheless, the excitement about axions is growing, and there are many plans to detect them. For example, axions are expected <a href="https://theconversation.com/this-australian-experiment-is-on-the-hunt-for-an-elusive-particle-that-could-help-unlock-the-mystery-of-dark-matter-187014">to convert into photons</a> when they pass through a magnetic field, so observations of photons with a certain energy are targeting stars with magnetic fields, such as neutron stars, or even <a href="https://home.cern/science/experiments/cast">the Sun</a>.</p>
<p>On the theoretical front, there are efforts to refine the predictions for what the universe would look like with different types of dark matter. For example, axions may be distinguished from WIMPs <a href="https://theconversation.com/new-look-at-einstein-rings-around-distant-galaxies-just-got-us-closer-to-solving-the-dark-matter-debate-204109">by the way they bend the light</a> through gravitational lensing.</p>
<p>With better observations and theory, we are hoping that the mystery of dark matter will soon be unlocked.</p><img src="https://counter.theconversation.com/content/226262/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andreea Font does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>We may be able to find traces of dark matter star explosions.Andreea Font, Reader in Theoretical Astrophysics, Liverpool John Moores UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2255022024-03-18T18:09:02Z2024-03-18T18:09:02ZFloating crystals slow stellar aging — for some stars, this can delay death by billions of years<p>Imagine the embers of a campfire, slowly dimming over time. That is the fate most stars in the universe face. After their nuclear fuel is spent, 98 per cent of stars — including our sun — will eventually become white dwarfs. These small, dense remnants are thought to <a href="https://esahubble.org/wordbank/white-dwarf/">simply cool down</a>, becoming ever fainter as the universe ages.</p>
<p>In 2019, astronomers discovered <a href="https://doi.org/10.3847/1538-4357/ab4989">a group of white dwarfs</a> that mysteriously stopped cooling. These “forever-young” stars remain at a near-constant surface temperature for at least eight billion years — an incredible length of time, considering the universe is <a href="https://www.space.com/24054-how-old-is-the-universe.html">13.8 billion years old</a>. </p>
<p>Something is fuelling these stars from within, but given that they had run out of their nuclear fuel source, scientists were unsure what could be keeping them shining so brightly. Our research, <a href="https://doi.org/10.1038/s41586-024-07102-y">recently published in <em>Nature</em></a>, presents the solution to this conundrum.</p>
<p>Using information gathered by the <a href="https://www.esa.int/Science_Exploration/Space_Science/Gaia">Gaia space observatory of the European Space Agency</a>, researchers discovered that some white dwarfs essentially stop cooling.</p>
<p>By studying how white dwarfs are distributed as a function of temperature (from hot to cold) <a href="https://sci.esa.int/web/gaia/-/61343-shedding-light-on-white-dwarfs-the-future-of-stars-like-our-sun">in the Gaia data</a>, astronomers noticed an accumulation of white dwarfs at intermediate temperatures. This indicates that some white dwarfs spend more time at these intermediate temperatures — eight billion years more than thought possible.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/nkXR7bpmy7Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Interview with University of Victoria astrophysics researcher Simon Blouin.</span></figcaption>
</figure>
<h2>Stellar crystals</h2>
<p>White dwarfs are weird. A mere teaspoon of material from their cores <a href="https://astronomy.swin.edu.au/cosmos/W/white+dwarf">weighs several tonnes</a>. Under such extreme densities, matter can behave strangely. Even though the interiors of white dwarfs are millions of degrees hot, the density is high enough that they can freeze into a solid state. They form crystals out of the carbon, oxygen and other elements present in their interiors.</p>
<p>The formation of these crystals normally starts at the centre of the star, where density is highest. As the white dwarf cools down, more crystals are formed in successive layers until almost the whole star is completely solid.</p>
<p>However, this inside-out crystallization does not apply to all white dwarfs. We discovered that the heaviest elements present in white dwarfs are expelled from the crystals as they are formed, just as <a href="https://nsidc.org/learn/parts-cryosphere/sea-ice/science-sea-ice">salt is expelled from ice crystals</a> when seawater freezes.</p>
<p>The crystals become less dense than their surroundings, and float up like ice cubes in a glass of water. As the crystals do not stay in place, the core cannot simply freeze from the inside out.</p>
<p>The movements created by the floating crystals reshuffle the chemical layering inside the star. Gradually, the heaviest elements are transported toward the centre. This releases a steady flow of gravitational energy that keeps the star shining at a near-constant temperature for billions of years.</p>
<p>Floating crystals can pause the stellar aging process, providing a final energy source to otherwise dead stars.</p>
<h2>The exception or the rule?</h2>
<p>So far, this cooling pause has been conclusively identified only for a small fraction of the white dwarf population. The high masses and peculiar compositions of these anomalous white dwarfs suggest that they had quite violent histories. Most likely, they are the products of stellar mergers — events where two stars collide and combine.</p>
<p>But this may be just the tip of the iceberg. Based on our findings, we suspect that almost all white dwarfs, and not just the merged ones, experience some cooling pause during their evolution. However, this more universal cooling pause would be much shorter than the multi-billion-year interruption studied so far.</p>
<p><a href="https://doi.org/10.1093/mnras/stad1719">Observations are ongoing</a> to try to identify this shorter cooling pause in the rest of the white dwarf population.</p>
<h2>Cosmic clocks</h2>
<p>These findings have implications for stellar archaeology. The cooler the white dwarf, the older it must be. Just as archeologists use carbon-14 dating to determine the age of artifacts and reconstruct the history of a city or civilization, astronomers rely on white dwarf cooling to measure the ages of stars and understand the history of our Milky Way galaxy.</p>
<p>Our discovery makes this more complicated. A white dwarf with a certain temperature could be billions of years older than initially assumed because of the formation of these floating crystals. The key now is to figure out which stars experience this cooling pause and which do not.</p><img src="https://counter.theconversation.com/content/225502/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Blouin receives funding from the Natural Sciences and Engineering Research Council of Canada. </span></em></p>Floating crystals can pause the stellar aging process, providing a final energy source to otherwise dead stars.Simon Blouin, CITA National Postdoctoral Fellow, Astrophysics, University of VictoriaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2254842024-03-12T17:51:07Z2024-03-12T17:51:07ZOur survey of the sky is uncovering the secrets of how planets are born<figure><img src="https://images.theconversation.com/files/580926/original/file-20240311-22-5v1m89.jpeg?ixlib=rb-1.1.0&rect=22%2C44%2C2978%2C1165&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Discs giving birth to new planets, seen by the Very Large Telescope.</span> <span class="attribution"><span class="source">ESO/C. Ginski, A. Garufi, P.-G. Valegård et al.</span></span></figcaption></figure><p>When we look out to the stars, it is typically not a yearning for the distant depths of outer space that drives us. When we are looking out there, we are truly looking back at ourselves. We try to understand our place in the unimaginable vastness of the universe. </p>
<p>One of the most burning questions that drives us is how unique we are. Did life only emerge here on Earth or is our galaxy teaming with it? </p>
<p>The very first step in finding out is to understand how special the Earth really is – and, by extension, our entire Solar System. This requires knowledge about how solar systems actually form. And that’s exactly what <a href="https://www.eso.org/public/news/eso2405/">my colleagues and I have started to uncover</a> with a new series of studies of star-forming regions.</p>
<p>In the past decades, astronomers <a href="https://theconversation.com/explainer-how-do-you-find-exoplanets-24153">have spotted</a> more than 5,000 planets around distant stars – so called exoplanets. We now know that planets are so abundant that you can look up to almost any star in the night sky and be near certain that planets are circling around it. But what do these planets look like?</p>
<p>The first planet that was discovered around a star similar to the Sun came as a shock to us. It was a so-called <a href="https://exoplanets.nasa.gov/resources/1040/hot-jupiter/">hot Jupiter</a>, a massive gas giant that orbits its parent star on such a tight orbit that the length of a year is only four days. This is a truly alien world with no equal in our own solar system.</p>
<p>From this first groundbreaking discovery, astronomers have gone on and found tightly packed systems of super-Earths, rocky planets several times as massive as the Earth, as well as awesome gas giants in century-long orbits around their parent star. Of the many planetary systems that we have found, none equals our own solar system. In fact <a href="https://theconversation.com/more-than-1-000-new-exoplanets-discovered-but-still-no-earth-twin-59274">most of them are quite different.</a> </p>
<p>To understand how all of these different systems come to be, we have to turn to the very beginning. And that’s majestic discs of dust and gas that surround the youngest stars. These are the nurseries which will eventually bring forth new planetary systems. </p>
<p>These discs <a href="https://arxiv.org/abs/2002.00405">are enormous objects</a>, up to several hundred times as extended as the distance between the Earth and the Sun. Yet in the sky they appear tiny. This is because even the nearest ones, which are practically in our galactic backyard, are between 600 and 1,600 light years away.</p>
<p>That is a tiny distance when you consider that the Milky Way galaxy has a diameter of more than 100,000 light years, but it still means that light, the fastest thing in the universe, takes up to 1,600 years to reach us from there. </p>
<p>The typical size of one of these planetary nurseries, as seen from the Earth, would be an angle of 1 “arc-second” on sky, which is equivalent to a 3,600th part of a degree. To put it in perspective, it is like trying to observe a person standing on top of the Eiffel Tower from 500km away in the Dutch capital of Amsterdam. </p>
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<p>To observe these discs we need the most advanced and largest telescopes. And we need sophisticated instruments that can correct for atmospheric turbulence which blurs our images. This is no mean feat of engineering, with the latest generation of instruments only being available since about a decade. </p>
<h2>New findings</h2>
<p>Using the European Southern Observatory’s “<a href="https://www.eso.org/public/unitedkingdom/teles-instr/paranal-observatory/vlt/">Very Large Telescope</a>”, the VLT, and the <a href="https://www.eso.org/sci/facilities/paranal/instruments/sphere.html">Sphere extreme adaptive optics camera</a>, we have now started to survey nearby young stars.</p>
<p>Our team, consisting of scientists from more than ten countries was able to observe more than 80 of these young stars in amazing detail – with our findings published in a <a href="https://www.eso.org/public/news/eso2405/">series of papers</a> in the journal Astronomy and Astrophysics.</p>
<p>All the images were taken in near infrared light, invisible to the human eye. They show the light from the distant young stars as it is reflected from the tiny dust particles in the discs. This dust is much like sand on the beach and will eventually clump together to form new planets. </p>
<p>What we found was an astonishing diversity of shape and form of these planetary nurseries. Some of them have huge ring systems, others large spiral arms. Some of them are smooth and calm, and yet others are caught in the middle of a storm as dust and gas from the surrounding star-forming clouds rains down on them. </p>
<p>While we expected some of this diversity, our survey shows for the first time that this holds true even within the same star-forming regions. So even planetary systems that form within the same neighbourhood might look quite different from one another.</p>
<figure class="align-center ">
<img alt="Planet-forming discs within the gas-rich cloud of Chamaeleon I, roughly 600 light-years from Earth." src="https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581242/original/file-20240312-22-tc1s5x.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Planet-forming discs within the gas-rich cloud of Chamaeleon I, roughly 600 light-years from Earth.</span>
<span class="attribution"><span class="source">Ginski et, al 2024</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Finding such wide range of discs suggests that the huge diversity in exoplanets discovered so far is a consequence of this broad spectrum of planetary nurseries. </p>
<p>Unlike the Sun, most stars in our galaxy have companions, with two or more stars orbiting a shared centre of mass. When looking at the constellation of Orion, we found that stars in groups of two or more were less likely to have large planet-forming discs than lone stars. This is a useful thing to know when hunting for exo-planets. </p>
<p>Another interesting finding was how uneven the discs in this region were, suggesting they may host massive planets that warp the discs. </p>
<p>The next step in our research will be to connect specific planets to their nurseries, to understand how the different systems might have formed in detail. We also want to zoom in even closer in the innermost regions of these discs in which terrestrial planets like our own Earth might already be forming.</p>
<p>For this, we will use the next generation of telescopes spearheaded by the “<a href="https://elt.eso.org/">Extremely Large Telescope</a>” of the European Southern Observatory that is right now under construction in the Chilean Atacama desert. </p>
<p>There are many questions to answer. But thanks to our survey we now know that the very first step on the long way for life to emerge is an utterly beautiful one.</p><img src="https://counter.theconversation.com/content/225484/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christian Ginski works for the University of Galway and frequently works with ESO facilities. </span></em></p>Astronomers have spotted a surprisingly diverse set of planet-forming disks.Christian Ginski, Lecturer of astronomy, University of GalwayLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2245642024-02-27T16:00:16Z2024-02-27T16:00:16ZA black hole discovery could force us to rethink how galaxies came to be<figure><img src="https://images.theconversation.com/files/578316/original/file-20240227-30-ntlqbc.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3834%2C2155&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2021/026/01F8QS893NVRJ6EYF0S46237KP?page=1&Tag=Active%20Galaxies/Quasars">NASA, ESA, Joseph Olmsted (STScI)</a></span></figcaption></figure><p>Peering deep into the infancy of the universe, the European Southern Observatory’s Very Large Telescope (VLT) recently confirmed the discovery of <a href="https://www.nature.com/articles/s41550-024-02195-x">the brightest and fastest growing quasar</a>. Quasars are <a href="https://esahubble.org/wordbank/quasar/">luminous objects in the night sky</a> powered by gas falling into a large black hole at the centre of a galaxy. </p>
<p>The discovery of this record-breaking object was fascinating enough. But another crucial aspect to the announcement is that it raises big questions about galaxy formation in the early universe. In particular, it remains puzzling how this quasar, which existed less than two billion years after the Big Bang, could have grown so large so quickly. Probing this conundrum could even lead to a rethink of how galaxies came to be.</p>
<p>Black holes, the densest objects in the universe, are given this name because their gravitational pull is so incredibly strong that not even light can escape their grasp. How then, can a black hole be the origin of such an intense light source? </p>
<p>Well, in some galaxies, <a href="https://science.nasa.gov/universe/black-holes/">where the black hole is sufficiently large</a>, matter is being drawn in at a ferociously high rate. As it spirals in, violent collisions between gases, dust, and stars result in the emission of huge amounts of light energy. The bigger the black hole, the more violent the collisions and the more light is emitted.</p>
<p>The quasar that was the subject of the latest study, known as J0529-4351, has a mass equivalent to 17 billion suns and is incredibly large. There is a spiralling disk of matter spanning a width of seven light years at the centre of the galaxy and the black hole is growing by accreting (accumulating) this matter. The disk’s width is comparable to the distance between Earth and <a href="https://www.britannica.com/place/Alpha-Centauri">the next nearest star system, Alpha Centauri</a>. </p>
<h2>Hiding in plain sight</h2>
<p>The black hole is growing rapidly by consuming a record-breaking amount of mass, equivalent to one sun each day. This intense accretion of matter releases an amount of radiative energy that’s equivalent to a quadrillion (thousand trillion) suns. </p>
<p>This raises the question of why an object so bright has only just been identified in the night sky, despite decades of astronomical observations. It turns out that this sneaky quasar had been hiding in plain sight.</p>
<p>Despite its astonishing luminosity, J0529-4351 is very distant, meaning that it seamlessly blends in among a sea of dimmer stars that lie much closer to Earth. In fact, this quasar is so far away that the light it emits takes a whopping 12 billion years to reach us here on Earth. </p>
<p>The age of the universe is around 13.7 billion years. So this quasar existed just 1.7 billion years after the <a href="https://science.nasa.gov/universe/the-big-bang/">Big Bang, at the beginning of the Universe</a>. </p>
<p>The universe’s expansion following the Big Bang is what permits us to measure the distance to, and therefore the age of, this quasar. A long-known simple <a href="https://www.bbc.co.uk/bitesize/guides/zphppv4/revision/3">formula called Hubble’s law</a>, states that knowing the velocity that an object is moving away from us allows us to calculate how far away it is.</p>
<figure class="align-center ">
<img alt="Very Large Telescope" src="https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/578312/original/file-20240227-26-rw2ozs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The object was confirmed using the Very Large Telescope facility in Chile.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/cerro-paranal-atacama-desert-chile-jan-750390019">Framalicious / Shutterstock</a></span>
</figcaption>
</figure>
<p>The collisions that occur as matter spirals into this quasar’s black hole raise it to scorching temperatures of 10,000°C. Under these conditions, the atoms in the system emit a characteristic spectrum of light. </p>
<p>These discrete frequencies of light form a sort of barcode that astronomers can use to identify the elemental compositions of objects in the night sky. As an object that’s emitting light moves away from us, the frequency of that observed light undergoes a shift, much like how the sound frequency of an ambulance siren shifts depending on whether it is driving towards or away from you. </p>
<p>This shift seen in astronomical objects is <a href="http://csep10.phys.utk.edu/OJTA2dev/ojta/c2c/galaxies/expanding/lookback_tl.html">known as redshift</a>. This, along with Hubble’s Law, has permitted both the age and the distance (both these properties are linked in cosmology) of J0529-4351 to be confirmed.</p>
<p>This bright beacon from the early universe has raised an important question that is baffling astronomers: how could this black hole, in such a relatively short period of time, grow so fast into such a massive object? Under well accepted models of the early universe, it should have taken longer for it to grow to this size. </p>
<p>What’s more, by tuning the artificial intelligence (AI) models used to scan telescope data for these unusual objects, more could still be found in the coming years. If they resemble J0529-4351, physicists would need to seriously rethink their models of the early universe and galaxy formation.</p>
<p>The fastest-growing black hole ever observed will be the perfect target for a system <a href="https://www.mpe.mpg.de/ir/gravityplus">called Gravity+</a>, an upcoming upgrade to an instrument on the Very Large Telescope called an interferometer. This interferometer is an ingenious way of combining data from the four separate telescopes that actually make up the VLT. </p>
<p>Gravity+ is designed to accurately measure the rotational speed and mass of black holes directly, especially those that lie far away from the Earth. </p>
<p>Furthermore, <a href="https://elt.eso.org/">the European Southern Observatory’s’s Extremely Large Telescope</a>, a 39-metre diameter reflecting telescope, is currently under construction in the Chilean Atacama Desert. This is designed for detecting the optical and near-infrared wavelengths characteristic of distant quasars and will make identifying and characterising such elusive objects even more likely in the future.</p><img src="https://counter.theconversation.com/content/224564/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robin Smith does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The discovery raises big questions about widely accepted models of galaxy formation.Robin Smith, Senior Lecturer in Physics, Sheffield Hallam UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2240412024-02-21T17:27:54Z2024-02-21T17:27:54ZThe brightest object ever observed in the night sky is a black hole that’s growing by the equivalent of one Sun a day<figure><img src="https://images.theconversation.com/files/576981/original/file-20240221-28-83koz3.jpg?ixlib=rb-1.1.0&rect=5%2C5%2C3828%2C2149&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/black-hole-slowly-rotating-space-event-2012670551">Merlin74 / Shutterstock</a></span></figcaption></figure><p><a href="https://www.nature.com/articles/s41550-024-02195-x">A new study</a> published in Nature Astronomy describes the most luminous object ever observed by astronomers. It is a black hole with a mass of 17 billion Suns, swallowing a greater amount of mass than the Sun every single day.</p>
<p>It has been known about for several decades, but since it is so bright, astronomers assumed it must be a nearby star. Only recent observations revealed its extreme distance and luminosity.</p>
<p>The object has been dubbed J0529-4351. This name simply refers to its coordinates on the celestial sphere – a way of projecting the objects in the sky onto the inside of a sphere. It is a type of <a href="https://esahubble.org/wordbank/quasar/">object called a quasar</a>.</p>
<p>The physical nature of quasars was initially unknown. But in 1963, the visible light from a <a href="https://www.wired.com/2008/08/dayintech-0805/">quasar called 3C 273</a> was split into all its wavelengths (known as its spectrum). This showed that it was located nearly 2 billion light years away. </p>
<p>Given how bright 3C 273 appears to us, and how far away it is, it must be extremely luminous – a term in astronomy that refers to the amount of light emitted by an object in a unit of time. The only known power source for such extreme luminosity was through material falling into a <a href="https://science.nasa.gov/universe/black-holes/">supermassive black hole</a>. Quasars are therefore the most actively growing black holes in the universe.</p>
<h2>Power source</h2>
<p>Supermassive black holes often sit at the centres of galaxies. As with all quasars, J0529-4351 is powered by material, mostly super-heated hydrogen and helium gas, falling into its black hole from the surrounding galaxy. </p>
<p>Roughly one times the Sun’s mass is falling into this black hole every day. Exactly how so much gas can be channelled into the centre of galaxies to increase the mass of black holes is an unanswered question in astrophysics.</p>
<p>At the galaxy’s centre, the gas forms into a thin disk shape. The properties of viscosity (resistance to the flow of matter in space) and friction in the thin disk help heat the gas to tens of thousands of degrees Celsius. This is hot enough to glow when viewed at ultraviolet and visible light wavelengths. It is that glow that we can observe from Earth. </p>
<p>At around 17 billion Suns in mass, J0529-4351 is not the most massive known black hole. One object, at the centre of the galaxy cluster Abell 1201, is <a href="https://www.space.com/largest-known-black-hole-discovered-through-gravitational-lensing">equivalent to 30 billion Suns</a>. However, we need to bear in mind that because of the time taken for light to travel across the vast distance between this object and Earth, we are witnessing it when the universe was only 1.5 billion years old. Its is now around 13.7 billion years old. </p>
<p>So this black hole must have been growing, or accreting, at this rate for a significant fraction of the age of the universe by the time it was observed. The authors believe the gas accretion by the black hole is happening close to the limit placed by the laws of physics. Faster accretion causes a more luminous disk of gas around the black hole which in turn can halt any more material falling in.</p>
<h2>Story of the discovery</h2>
<p>J0529-4351 has been known about for decades, but despite having an accretion disk of gas 15,000 times larger than our Solar System and occupying its own galaxy – which is probably close to the size of the Milky Way – it is so far away, it appears as a single point of light in our telescopes.</p>
<p>This means it is difficult to distinguish from the billions of stars in our own galaxy. To discover that it is in fact a distant, powerful, supermassive black hole required some more complex techniques. Firstly, astronomers collected light from the middle of the infrared waveband (light with much longer wavelengths than those we can see). </p>
<p>Stars and quasars look quite different to one another at those wavelengths. To confirm the observation, a spectrum was taken (much as it was with the quasar 3C 273), using the <a href="https://rsaa.anu.edu.au/observatories/telescopes/anu-23m-telescope">Australian National University’s 2.3 metre telescope</a> at Siding Spring Observatory, New South Wales. </p>
<p>And, as with 3C 273, the spectrum revealed both the nature of the object and how far away it was – 12 billion light years. This highlighted how extreme its luminosity must be.</p>
<h2>Detailed checks</h2>
<p>Despite these measurements, a number of checks needed to be made to confirm the true luminosity of the quasar. Firstly, astronomers needed to make sure that the light had not been magnified by a source in the sky that was closer to Earth. Much like lenses used in spectacles or binoculars, galaxies can act as lenses. They are so dense that they can bend and magnify the light of more distant sources that are perfectly aligned behind them. </p>
<p>Data from the European Space Agency’s Gaia satellite, which has extremely precise measurements of J0529-4351’s position, was used to determine that J0529-4351 is truly a single non-lensed source of light in the sky. This is backed up by more detailed spectra taken with the <a href="https://www.eso.org/public/unitedkingdom/teles-instr/paranal-observatory/vlt/">European Southern Observatory’s Very Large Telescope</a> (VLT) facility in Chile. </p>
<p>J0529-4351 is likely to become a very significant tool for the future study of quasars and black hole growth. The mass of black holes is a fundamental property but is very difficult to measure directly, as there is no standard set of weighing scales for such absurdly large, mysterious objects. </p>
<p>One technique is to measure the effect the black hole has on more diffuse gas orbiting it in large clouds, called the “broad line region”. This gas is revealed in the spectrum through wide “emission lines”, which are caused by electrons jumping between specific energy levels in the ionised gas. </p>
<p>The width of these lines is directly related to the mass of the black hole, but the calibration of this relationship is very poorly tested for the most luminous objects such as J0529-4351. However, because it is so physically large and so luminous, J0529-4351 will be observable by a new instrument being installed on the VLT, <a href="https://www.eso.org/public/unitedkingdom/teles-instr/paranal-observatory/vlt/vlt-instr/gravity+/">called Gravity+</a>. </p>
<p>This instrument will give a direct measurement of the black hole mass and calibrate the relationships used to estimate masses in other high-luminosity objects.</p><img src="https://counter.theconversation.com/content/224041/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Philip Wiseman works at the University of Southampton and is funded by the Science and Technology Facilities Council.</span></em></p>The extreme object could tell us more about the environment around black holes.Philip Wiseman, Research Fellow, Astronomy, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2232472024-02-12T19:33:22Z2024-02-12T19:33:22ZNewborn gas planets may be surprisingly flat – new research<p>A new planet starts its life in a rotating circle of gas and dust, a cradle known as a <a href="https://esahubble.org/wordbank/circumstellar-disc/">protostellar disc</a>. My colleagues and I have used computer simulations to show that newborn gas planets in these discs are likely to have surprisingly flattened shapes. This finding, <a href="https://www.aanda.org/articles/aa/full_html/2024/02/aa48753-23/aa48753-23.html">published in Astronomy and Astrophysics Letters</a>, could add to our picture of exactly how planets form.</p>
<p>Observing protoplanets that have just formed and are still within their protostellar discs is extremely difficult. Until now only three such young protoplanets have been observed, with two of them in the same system, PDS 70.</p>
<p>We need to find systems that are young, and close enough for our telescopes to be able to detect the dim light from the planet itself and distinguish it from that of the disc. The whole process of planetary formation lasts only a few million years which is nothing more than a blink of an eye in astrophysical scales. This means we need to have luck to catch them in the act of forming.</p>
<p>Our research group performed computer simulations to determine the properties of gaseous protoplanets under a variety of thermal conditions in the planets’ cradles. </p>
<p>The simulations have enough resolution to be able to follow the evolution of a protoplanet in the disc from an early stage, when it is just a mere condensation within the disc. Such simulations are computationally demanding and were run on <a href="https://dirac.ac.uk/">DiRAC, the UK’s astrophysics supercomputing facility</a>.</p>
<p>Typically, multiple planets form within a disc. The study found that protoplanets have a shape known as oblate spheroids, like Smarties or M&M’s, rather than being spherical. They grow by drawing gas predominantly through their poles rather than their equators. </p>
<p>Technically, the planets in our Solar System are also oblate spheroids but their flattening is small. <a href="https://spaceplace.nasa.gov/planets-round/en/#:%7E:text=Mercury%20and%20Venus%20are%20the,bit%20thicker%20in%20the%20middle.">Saturn has a flattening of 10%, Jupiter 6%, whereas Earth a mere 0.3%</a>.</p>
<p>In comparison, the typical flattening of protoplanets is 90%. Such a flattening will affect the observed properties of protoplanets, and it needs to be taken into account when interpreting observations.</p>
<h2>How planets start off</h2>
<p>The most widely accepted theory for planet formation <a href="https://faculty.ucr.edu/%7Ekrice/coreacc.html#:%7E:text=The%20most%20commonly%20accepted%20mechanism,to%20accrete%20a%20gaseous%20envelope.">is that of “core accretion”</a>. According to this model, tiny dust particles smaller than sand collide with each other, group together and progressively grow into larger and larger bodies. This is effectively what happens to the dust under your bed when it isn’t cleaned. </p>
<p>Once a core of dust with enough massive forms, it draws gas from the disc to form a gas giant planet. This bottom-to-top approach would take a few million years. </p>
<p>The opposite, top-to-bottom approach, is the <a href="https://blog.planethunters.org/tag/disk-instability/">theory of disc instability</a>. In this model, the protostellar discs that attend young stars are gravitationally unstable. In other words, they are too heavy to be maintained and so fragment into pieces, which evolve into planets. </p>
<p>The theory of core accretion has been around for a long time and it can explain many aspects of how our Solar System formed. However, disc instability can better explain some of the exoplanetary systems we have discovered in recent decades, such as those where a gas giant planet orbits very very far from its host star.</p>
<p>The appeal of this theory is that planet formation happens very fast, within a few thousand years, which is consistent with observations that suggest planets exist in very young discs.</p>
<p>Our study focused on gas giant planets formed via the model of disc instability. They are flattened because they form from the compression of an already flat structure, the protostellar disc, but also because of how they rotate. </p>
<h2>No flat Earths</h2>
<p>Although these protoplanets overall are very flattened, their cores, which will eventually evolve into gas giant planets as we know them, are less flattened – only by about 20%. This is just twice the flattening of Saturn. With time they are expected to become more spherical.</p>
<p>Rocky planets, like Earth and Mars, cannot form via disc instability. They are thought to form by slowly assembling dust particles to pebbles, rocks, kilometre-sized objects and eventually planets. They are too dense to be significantly flattened even when they are newly born. There is no possibility that Earth was flattened at such a high degree when it as young.</p>
<p>But our study does support a role for disc instability in the case of some worlds in some planetary systems.</p>
<p>We are now moving from the era of exoplanet discoveries to the era of exoplanet characterisation. Many new observatories are set to become operational. These will help discover more protoplanets embedded in their discs. Predictions from computer models are also becoming more sophisticated. </p>
<p>The comparison between these theoretical models and observations is bringing us closer and closer to understanding the origins of our Solar System.</p><img src="https://counter.theconversation.com/content/223247/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dimitris Stamatellos receives funding from the Science and Technology Facilities Council (STFC).</span></em></p>The observation could fill in gaps in our knowledge about planet formation.Dimitris Stamatellos, Associate Professor in Astrophysics, University of Central LancashireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2189212023-12-28T20:38:02Z2023-12-28T20:38:02ZWant to get into stargazing? A professional astronomer explains where to start<p>There are few things more peaceful and relaxing than a night under the stars. Through the holidays, many people head <a href="https://www.lightpollutionmap.info/#zoom=3.80&lat=-28.5041&lon=129.6954&state=eyJiYXNlbWFwIjoiTGF5ZXJCaW5nUm9hZCIsIm92ZXJsYXkiOiJ3YV8yMDE1Iiwib3ZlcmxheWNvbG9yIjpmYWxzZSwib3ZlcmxheW9wYWNpdHkiOjYwLCJmZWF0dXJlc29wYWNpdHkiOjg1fQ==">away from the bright city lights</a> to go camping. They revel in the dark skies, spangled with myriad stars.</p>
<p>As a child, I loved such trips, and they helped cement my passion for the night sky, and for all things space. </p>
<p>One of my great joys as an astronomer is sharing the night sky with people. There is something wondrous about helping people stare at the cosmos through a telescope, getting their first glimpses of the universe’s many wonders. But we can also share and enjoy the night sky just with our own eyes – pointing out the constellations and the planets, or discovering <a href="https://theconversation.com/the-geminids-the-years-best-meteor-shower-is-upon-us-and-this-one-will-be-a-true-spectacle-218923">the joys of watching meteor showers</a>.</p>
<p>It is easy to be bitten by the astronomy bug, and a common question I get asked is “how can I get more into stargazing?”. Here are ways to get started in this fascinating and timeless hobby that won’t break the bank.</p>
<h2>Learning the night sky</h2>
<p>A good place to start if you’re a budding astronomer is to learn your way around the night sky. When I was young, this involved getting hold of a planisphere (a star map, <a href="https://in-the-sky.org/planisphere/index.php">you can make your own here</a>), or a <a href="https://www.amazon.com.au/Turn-Left-Orion-Hundreds-Telescope-ebook/dp/B07H4KN8G2">good reference book</a>. </p>
<p>Today, there are <a href="https://www.space.com/best-stargazing-apps">countless good apps</a> to help you find your way around the night sky. </p>
<p>A great example of such an app is <a href="https://stellarium-web.org/">Stellarium</a> – a planetarium program allowing you to view the night sky from the comfort of your room or to plan an evening’s observing ahead of schedule.</p>
<p>To memorise the night sky, you can try star hopping. Pick out a bright, famous, easy to find constellation, and use it as a guide to help you identify the constellations around it. </p>
<p>Learn one constellation per week, and within a year, you’ll be familiar with most of <a href="https://www.iau.org/public/themes/constellations/">the constellations</a> visible from your location.</p>
<p>Let’s use Orion as an example. The slider below shows images from Stellarium, with Orion riding high in the sky on a summer’s evening. I’ve added arrows to show how you can use Orion (shown in the centre of the map below) to hop around the summer sky.</p>
<p><iframe id="tc-infographic-1007" class="tc-infographic" height="400px" src="https://cdn.theconversation.com/infographics/1007/811d84689c71ac5c004a402a84a7fb446f0ae803/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>To learn the constellations around Orion, your task is relatively straightforward. Head out on a clear, dark summer’s night, and find Orion high to the north. The three stars of Orion’s belt are a fantastic signpost to Orion’s neighbours. </p>
<p>If you follow the line of the belt upwards and to the right, you come to <a href="https://en.wikipedia.org/wiki/Sirius">Sirius</a> – the brightest star in the night sky, and the brightest star in <a href="https://en.wikipedia.org/wiki/Canis_Major">Canis Major</a>, the big hunting dog. Carry the line on and curve to the left as you go, and you’ll find <a href="https://en.wikipedia.org/wiki/Canopus">Canopus</a>, the second brightest star in the sky.</p>
<p>Now come back to Orion’s belt, and follow its line down and to the left. You’ll come to a V-shaped group of stars, including the bright red <a href="https://en.wikipedia.org/wiki/Aldebaran">Aldebaran</a>. This is the <a href="https://en.wikipedia.org/wiki/Hyades_(star_cluster)">Hyades star cluster</a> (with Aldebaran a foreground interloper), which makes up the head of <a href="https://en.wikipedia.org/wiki/Taurus_(constellation)">Taurus</a>, the bull.</p>
<p>Take the line further, and you come to <a href="https://www.space.com/pleiades.html">the Pleiades</a> – often known as the Seven Sisters – a beautiful star cluster easily visible to the naked eye.</p>
<p>Back to Orion again. This time, you’re going to draw a line from <a href="https://en.wikipedia.org/wiki/Rigel">Rigel</a> (the bright star at the top-left of Orion’s boxy body) through <a href="https://en.wikipedia.org/wiki/Betelgeuse">Betelgeuse</a> (the bright red star at the lower-right of the box) and continue it towards the horizon. This takes you to <a href="https://en.wikipedia.org/wiki/Gemini_(constellation)">Gemini</a> – the twins.</p>
<p>Just by using Orion as the signpost, you can find your way to a good number of constellations (the cyan line points to <a href="https://en.wikipedia.org/wiki/Lepus_(constellation)">Lepus</a>, the hare; the white line to <a href="https://en.wikipedia.org/wiki/Canis_Minor">Canis Minor</a>, the little hunting dog). </p>
<p>By star hopping, you’ll slowly but surely learn your way around the night sky until the constellations become familiar friends.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/kindred-skies-ancient-greeks-and-aboriginal-australians-saw-constellations-in-common-74850">Kindred skies: ancient Greeks and Aboriginal Australians saw constellations in common</a>
</strong>
</em>
</p>
<hr>
<h2>Virtual observing</h2>
<p>Looking at the sky with the naked eye is a wonderful thing, but it’s also great to zoom in and see more detail.</p>
<p>What if you don’t have access to binoculars or a telescope of your own? Thankfully, software like Stellarium can give you a fantastic virtual observing experience.</p>
<p>Imagine you want to see Saturn’s rings – a spectacular sight through even a small telescope. You can easily do this with Stellarium. Find Saturn by using the search bar and click on it to bring up the planet’s info. </p>
<p>Click on the cross-hair symbol to “lock on”, then zoom in. The further you zoom in, the more you’ll see. You can even run the clock forwards or backwards to see the planet’s moons move in their orbits, or the tilt of Saturn’s rings <a href="https://theconversation.com/will-saturns-rings-really-disappear-by-2025-an-astronomer-explains-217370">changing from our viewpoint over time</a>.</p>
<p>A virtual observing session is as simple as that – just pan around the sky until you find something you want to see, and zoom in.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up of rotating Saturn" src="https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=437&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=437&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=437&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=549&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=549&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564091/original/file-20231207-17-qvar43.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=549&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Example of using the clock feature in Stellarium to see the movement of Saturn’s moons.</span>
<span class="attribution"><span class="source">Stellarium</span></span>
</figcaption>
</figure>
<h2>A hobby best shared</h2>
<p>Now, a virtual observing session is great, but it pales compared to the real thing. I’d recommend using planetarium programs like Stellarium to figure out what you want to see, then heading out to look at it with your own eyes.</p>
<p>Astronomy is a wonderful hobby, and one that is best shared. Most towns and cities have their own astronomy clubs, and they’re usually more than happy to welcome guests who want to gaze at the night sky. </p>
<p>I joined my local astronomy society, the <a href="https://www.wyas.org.uk/">West Yorkshire Astronomical Society</a> in the United Kingdom, when I was just eight years old. I owe them so much. The members were incredibly supportive of a young kid with so many questions, and I genuinely believe I would not be where I am today without their help. As a member, I saw firsthand just how fantastic the amateur astronomy community is. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A telescope inside a dome during daytime, with a young teen and two older men standing next to it" src="https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=438&fit=crop&dpr=1 600w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=438&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=438&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=550&fit=crop&dpr=1 754w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=550&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/562685/original/file-20231130-29-ogkxpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=550&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The author Jonti Horner at age 16, showing then Astronomer Royal of the UK, Arnold Wolfendale (right), the WYAS 18-inch telescope, hand-made by members. Also seen is the society’s then president, Ken Willoughby.</span>
<span class="attribution"><span class="source">Alan Horner, author provided</span></span>
</figcaption>
</figure>
<p>At the society, we had weekly talks on astronomy, given by the club members and visiting astronomers from local universities. We also had regular night sky viewing nights, using the society’s very own telescope – a behemoth the members had built themselves. </p>
<p>People who are passionate about their hobby love nothing more than sharing it with others. The members of astronomical societies are fantastic guides to the night sky, and they often have incredible equipment they’re more than happy to share with you.</p>
<p>Both astronomy clubs and universities often offer public night sky viewing nights, which are the perfect opportunity to peer at the sky through a telescope, with an experienced guide on hand to find the most impressive sights to share. </p>
<p>So, if you want to learn more about the night sky, reach out to your local astronomy society – it could be the start of something very special.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/want-to-buy-a-home-telescope-tips-from-a-professional-astronomer-to-help-you-choose-218604">Want to buy a home telescope? Tips from a professional astronomer to help you choose</a>
</strong>
</em>
</p>
<hr>
<p><em>If you want to find a local astronomy group, check out <a href="https://astronomy.org.au/amateur/amateur-societies/australia/">this list</a>. If you’re a member of a group that isn’t listed, please reach out to get them to update the list using the ‘Contact Us’ link.</em></p><img src="https://counter.theconversation.com/content/218921/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>People have been looking up at the stars for thousands of years. Here’s where to start if you want to learn more about the night sky – from spotting easy-to-find constellations to using the best apps.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2058102023-10-16T12:30:12Z2023-10-16T12:30:12ZWhy is space so dark even though the universe is filled with stars?<figure><img src="https://images.theconversation.com/files/538108/original/file-20230718-17-5jcl17.jpg?ixlib=rb-1.1.0&rect=26%2C6%2C996%2C676&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This age old question has been dubbed Olbers' paradox.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-milky-way-appears-over-the-valle-de-la-luna-in-the-news-photo/1418507439?adppopup=true">John Moore via Getty Images News</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why is space so dark despite all of the stars in the universe? – Nikhil, age 15, New Delhi</strong></p>
</blockquote>
<hr>
<p>People have been asking why space is dark despite being filled with stars for so long that this question has a special name – <a href="https://lambda.gsfc.nasa.gov/product/suborbit/POLAR/cmb.physics.wisc.edu/tutorial/olbers.html">Olbers’ paradox</a>.</p>
<p>Astronomers estimate that there are about <a href="https://theconversation.com/how-many-stars-are-there-in-space-165370">200 billion trillion stars</a> in the observable universe. And many of those stars are as bright or even brighter than our sun. So, why isn’t space filled with dazzling light?</p>
<p><a href="http://www.astrojack.com/">I am an astronomer</a> who studies stars and planets – including those outside our solar system – and their motion in space. The study of distant stars and planets helps <a href="https://scholar.google.com/citations?user=pF3HbeQAAAAJ&hl=en&oi=ao">astronomers like me</a> understand why space is so dark.</p>
<hr>
<iframe id="noa-web-audio-player" style="border: none" src="https://embed-player.newsoveraudio.com/v4?key=x84olp&id=https://theconversation.com/why-is-space-so-dark-even-though-the-universe-is-filled-with-stars-205810&bgColor=F5F5F5&color=D8352A&playColor=D8352A" width="100%" height="110px"></iframe>
<p><em>You can listen to more articles from The Conversation, narrated by Noa, <a href="https://theconversation.com/us/topics/audio-narrated-99682">here</a>.</em></p>
<hr>
<p>You might guess it’s because a lot of the stars in the universe are very far away from Earth. Of course, it is true that the farther away a star is, the less bright it looks – <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/isq.html">a star 10 times farther away looks 100 times dimmer</a>. But it turns out this isn’t the whole answer. </p>
<h2>Imagine a bubble</h2>
<p>Pretend, for a moment, that the universe is so old that the light from even the farthest stars has had time to reach Earth. In this imaginary scenario, all of the stars in the universe are not moving at all.</p>
<p>Picture a large bubble with Earth at the center. If the bubble were about 10 <a href="https://exoplanets.nasa.gov/faq/26/what-is-a-light-year/">light years</a> across, it would contain about <a href="https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs">a dozen stars</a>. Of course, at several light years away, many of those stars would look pretty dim from Earth. </p>
<p>If you keep enlarging the bubble to 1,000 light years across, then to 1 million light years, and then 1 billion light years, the farthest stars in the bubble will look even more faint. But there would also be more and more stars inside the bigger and bigger bubble, all of them contributing light. Even though the farthest stars look dimmer and dimmer, there would be a lot more of them, and the whole night sky should look very bright.</p>
<p>It seems I’m back where I started, but I’m actually a little closer to the answer.</p>
<h2>Age matters</h2>
<p>In the imaginary bubble illustration, I asked you to imagine that the stars are not moving and that the universe is very old. But the universe is only about <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question28.html">13 billion years old</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Image of lightly colored galaxies and stars against dark background" src="https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=613&fit=crop&dpr=1 600w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=613&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=613&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=770&fit=crop&dpr=1 754w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=770&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=770&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Galaxies as they appeared approximately 13.1 billion years ago, taken by the James Webb Space Telescope.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/image-released-by-nasa-on-july-11-2022-shows-galaxy-cluster-news-photo/1241872380?adppopup=true">NASA/ESA/CSA/STScI/Handout from Xinhua News Agency via Getty Images</a></span>
</figcaption>
</figure>
<p>Even though that’s an amazingly long time in human terms, it’s short in astronomical terms. It’s short enough that the light from stars more distant than about 13 billion light years hasn’t actually reached Earth yet. And so the actual bubble around Earth that contains all the stars we can see only extends out to about <a href="https://science.nasa.gov/observable-universe">13 billion light years from Earth</a>.</p>
<p>There just are not enough stars in the bubble to fill every line of sight. Of course, if you look in some directions in the sky, you can see stars. If you look at other bits of the sky, you can’t see any stars. And that’s because, in those dark spots, the stars that could block your line of sight are so far away their light hasn’t reached Earth yet. As time passes, light from these more and more distant stars will have time to reach us. </p>
<h2>The Doppler shift</h2>
<p>You might ask whether the night sky will eventually light up completely. But that brings me back to the other thing I told you to imagine: that all of the stars are not moving. The universe is actually expanding, with the most distant galaxies <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/redshift.html">moving away from Earth at nearly the speed of light</a>. </p>
<p>Because the galaxies are moving away so fast, the light from their stars is pushed into colors the human eye can’t see. This effect is called the <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/redshift.html">Doppler shift</a>. So, even if it had enough time to reach you, <a href="https://svs.gsfc.nasa.gov/12856">you still couldn’t see</a> the light from the most distant stars with your eyes. And the night sky would not be completely lit up. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ikgRZt1BSyk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Doppler shift, also known as the redshift, is a phenomenon in which light from objects that are moving away from an observer appears more toward the red end of the spectrum.</span></figcaption>
</figure>
<p>If you wait even longer, eventually the stars will all burn out – <a href="https://astronomy.swin.edu.au/cosmos/m/main+sequence+lifetime">stars like the sun last only about 10 billion years</a>. Astronomers hypothesize that in the distant future – a thousand trillion years from now – the universe will go dark, <a href="https://en.wikipedia.org/wiki/The_Five_Ages_of_the_Universe">inhabited by only stellar remnants</a> like white dwarfs and black holes.</p>
<p>Even though our night sky isn’t completely filled with stars, we live in a very special time in the universe’s life, when we’re lucky enough to enjoy a rich and complex night sky, filled with light and dark.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/205810/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brian Jackson receives federally funded research grants from NASA. </span></em></p>An astronomer explains why space looks so dark despite containing 200 billion trillion stars.Brian Jackson, Associate Professor of Astronomy, Boise State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2154662023-10-11T15:14:41Z2023-10-11T15:14:41ZThe afterglow of an explosive collision between giant planets may have been detected in a far-off star system<figure><img src="https://images.theconversation.com/files/553243/original/file-20231011-25-y5wvfs.jpeg?ixlib=rb-1.1.0&rect=2%2C0%2C1914%2C1431&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A visualisation of the huge, glowing planetary body produced by a planetary collision.</span> <span class="attribution"><a class="source" href="https://www.eurekalert.org/multimedia/1001427">Mark Garlick</a>, <span class="license">Author provided</span></span></figcaption></figure><p>The afterglow of a massive collision between two giant planets may have been detected for the first time. The wreckage of the collision could eventually cool and form an entirely new planet. If the observation is confirmed, it provides an amazing opportunity to watch the birth of a new world in real time and open a window into how planets form.</p>
<p>In December 2021, astronomers watching an otherwise unremarkable sun-like star <a href="https://astronomerstelegram.org/?read=14879">saw it begin to flicker</a>. For a few months, the visible light (the light we can see with our eyes) from this star continued to change. At times it would almost disappear, before returning to its previous brightness. </p>
<p>The star, which sits roughly 1,800 light years from Earth, was given the identifier ASASSN-21qj, after the <a href="https://www.astronomy.ohio-state.edu/asassn/">ASASN-SN astronomy survey</a> that first observed the star’s dimming. </p>
<p>Seeing stars dim like this is not uncommon. It’s generally attributed to material passing between the star and Earth. ASASSN-21qj may just have been added to a growing list of similar observations had it not been for an amateur astronomer, <a href="https://science.nasa.gov/people/arttu-sainio/">Arttu Sainio</a>. Sainio pointed out on social media that some two and a half years before the star’s light was seen to fade, the emission of infrared light coming from its location rose by roughly 4%. </p>
<p>Infrared light is most strongly emitted by objects at relatively high temperatures of a few hundred degrees Celsius. This posed the questions: were these two observations related and, if so, what the heck was going on around ASASSN-21qj?</p>
<h2>Planetary cataclysm</h2>
<p>Publishing our findings <a href="https://www.nature.com/articles/s41586-023-06573-9">in Nature</a>, we propose that both sets of observations could be explained by a cataclysmic collision between two planets. Giant impacts, as such collisions are known, are thought to be common in the final stages of the formation of planets. They dictate the final sizes, compositions, and thermal states of planets and mould the orbits of objects in those planetary systems. </p>
<p>In our solar system, giant impacts are thought to be responsible for the <a href="https://science.nasa.gov/uranus/facts/">odd tilt of Uranus</a>, the <a href="https://science.nasa.gov/mercury/facts/">high density of Mercury</a> and the <a href="https://news.uchicago.edu/explainer/formation-earth-and-moon-explained#moonform">existence of Earth’s Moon</a>. However, until now, we had little direct evidence of giant impacts ongoing in the galaxy. </p>
<figure class="align-center ">
<img alt="Artist's impression of the WISE telescope." src="https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553260/original/file-20231011-19-jdcjpm.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Nasa’s WISE telescope observed an increase in the infrared light coming from the star.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA17254">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>In order to explain the observations, a collision would have needed to release more energy in the first few hours after impact than would be emitted from the star. Material from the colliding bodies would have been superheated and melted, vaporised or both.</p>
<p>The impact would have formed a hot, glowing mass of material hundreds of times larger than the original planets. The infrared brightening of ASASSN-21qj was observed by <a href="https://www.jpl.nasa.gov/missions/wide-field-infrared-survey-explorer-wise">Nasa’s WISE space telescope</a>. WISE only looks at the star every 300 days or so, and probably missed the initial flash of light from the impact. </p>
<p>However, the expanded planetary body produced by the impact will take a long time, perhaps millions of years, to cool and shrink to something we might recognise as a new planet. Initially, when this “post-impact body” was at its greatest extent, the light emitted from it could still be as high as several percent of emission from the star. Such a body could have produced the infrared brightening that we saw.</p>
<p>The impact would also have ejected great plumes of debris into a range of different orbits around the star. A fraction of this debris would have been vaporised by the shock of the impact, later condensing to form clouds of tiny ice and rock crystals. Over time, some of this clumpy cloud of material passed between ASASSN-21qj and Earth, blocking out a fraction of the visible light from the star and producing the erratic dimming. </p>
<figure class="align-center ">
<img alt="Neptune." src="https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=753&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=753&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553274/original/file-20231011-25-9485zg.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=753&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The planets may have been similar to Neptune in the solar system.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA01492">NASA/JPL</a></span>
</figcaption>
</figure>
<p>If our interpretation of the events is correct, studying this star system could help us understand a key mechanism of planet formation. Even from the limited set of observations we have so far, we have learned some very interesting things. </p>
<p>Firstly, to emit the amount of energy observed, the post-impact body must have been many hundreds of times the size of Earth. To create a body that large, the planets that collided must each have been several times the mass of Earth – possibly as large as the <a href="https://www.lpi.usra.edu/opag/outer_planets.pdf">“ice giant”</a> planets Uranus and Neptune. </p>
<p>Secondly, we estimate the temperature of the post-impact body to be around 700°C. For the temperature to be that low, the colliding bodies could not have been entirely made of rock and metal. </p>
<h2>Ice giants</h2>
<p>The outer regions of at least one of the planets must have contained elements with low boiling temperatures, such as in water. We therefore think that we have seen a collision between two Neptune-like worlds that are rich in ice. </p>
<p>The delay that was seen between the emission of infrared light and the observation of debris crossing the star suggests that the collision took place quite far away from the star – further away than the Earth is from the Sun. Such a system, in which there are ice giants far from the star, is more similar to our solar system than to many of the tightly-packed planetary systems astronomers often observe around other stars.</p>
<p>The most exciting aspect of this is that we can continue to watch the system evolve for many decades and test our conclusions. Future observations, using telescopes such as <a href="https://webbtelescope.org/home">Nasa’s JWST</a>, will determine the sizes and compositions of particles in the debris cloud, identify the chemistry of the upper layers of the post-impact body and track how this hot mass of debris cools down. We may even see new moons emerge. </p>
<p>These observations can inform our theories, helping us understand how giant impacts shape planetary systems. So far the only examples we’ve had are the echoes of impacts in our own solar system. We will now be able to watch the birth of a new planet in real time.</p><img src="https://counter.theconversation.com/content/215466/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Lock receives funding from the UK Natural Environment Research Council (grant NE/V014129/1).</span></em></p><p class="fine-print"><em><span>Zoe Leinhardt receives funding from UK Science and Technology Facilities Council (grant number ST/V000454/1). </span></em></p><p class="fine-print"><em><span>Matthew Kenworthy does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The discovery provides a way to study the birth of an entirely new planet in real time.Simon Lock, NERC Research Fellow, School of Earth Sciences, University of BristolMatthew Kenworthy, Associate professor in Astronomy, Leiden UniversityZoe Leinhardt, Associate Professor, School of Physics, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2058092023-10-02T12:29:02Z2023-10-02T12:29:02ZHow do astronomers know the age of the planets and stars?<figure><img src="https://images.theconversation.com/files/529821/original/file-20230602-6875-7ttf8v.jpg?ixlib=rb-1.1.0&rect=1%2C16%2C1005%2C671&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Astronomers can estimate ages for stars outside the Solar System, but not planets.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-constellation-sagittarius-taken-from-the-u-s-naval-news-photo/615295876?adppopup=true">Corbis Historical via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>How do we know the age of the planets and stars? – Swara D., age 13, Thane, India</strong></p>
</blockquote>
<hr>
<p>Measuring the ages of planets and stars helps scientists understand when they formed and how they change – and, in the case of planets, if <a href="https://theconversation.com/ancestor-of-all-life-on-earth-evolved-earlier-than-we-thought-according-to-our-new-timescale-101752">life has had time to have evolved on them</a>.</p>
<p>Unfortunately, age is hard to measure for objects in space.</p>
<p>Stars like the Sun maintain the same <a href="https://en.wikipedia.org/wiki/Stellar_evolution">brightness, temperature and size for billions of years</a>. Planet properties <a href="https://en.wikipedia.org/wiki/Planetary_equilibrium_temperature">like temperature</a> are often set by the star they orbit rather than their own age and evolution.</p>
<p>Determining the age of a star or planet can be as hard as guessing the age of a person who looks exactly the same from childhood to retirement. </p>
<h2>Sussing out a star’s age</h2>
<p>Fortunately, <a href="http://astronomy.nmsu.edu/jasonj/565/docs/11_07.pdf">stars change subtly</a> in brightness and color over time. With very accurate measurements, astronomers can compare these measurements of a star to <a href="https://doi.org/10.3847/0067-0049/222/1/8">mathematical models</a> that predict what happens to stars as they get older and estimate an age from there. </p>
<p>Stars don’t just glow, they also spin. Over time, <a href="https://doi.org/10.1086/151310">their spinning slows down</a>, similar to how a spinning wheel slows down when it encounters friction. By comparing the spin speeds of stars of different ages, astronomers have been able to <a href="https://doi.org/10.1086/367639">create mathematical relationships for the ages of stars</a>, a method known as <a href="https://en.wikipedia.org/wiki/Gyrochronology">gyrochronology</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up image of the Sun in outer space" src="https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=567&fit=crop&dpr=1 600w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=567&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=567&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=713&fit=crop&dpr=1 754w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=713&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=713&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Researchers estimate the Sun is 4.58 billion years old.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/in-this-handout-photo-provided-by-nasa-a-solar-and-news-photo/2740385?adppopup=true">NASA via GettyImages</a></span>
</figcaption>
</figure>
<p>A star’s spin also generates a strong magnetic field and produces magnetic activity, such as <a href="https://en.wikipedia.org/wiki/Solar_flare">stellar flares</a> – powerful bursts of energy and light that occur on stars’ surfaces. A steady decline in magnetic activity from a star can also help estimate its age.</p>
<p>A more advanced method for determining the ages of stars is called <a href="https://en.wikipedia.org/wiki/Asteroseismology">asteroseismology</a>, or star shaking. Astronomers study vibrations on the surfaces of stars caused by waves that travel through their interiors. Young stars have different vibrational patterns than old stars. By using this method, <a href="https://doi.org/10.1051/0004-6361/201526419">astronomers have estimated</a> the Sun to be 4.58 billion years old.</p>
<h2>Piecing together a planet’s age</h2>
<p>In the solar system, <a href="https://en.wikipedia.org/wiki/Radionuclide">radionuclides</a> are the key to dating planets. These are special atoms that slowly release energy over a long period of time. As natural clocks, radionuclides help scientists determine the ages of all kinds of things, from <a href="https://www.nps.gov/subjects/geology/radiometric-age-dating.htm">rocks</a> to <a href="https://theconversation.com/radiocarbon-dating-only-works-half-the-time-we-may-have-found-the-solution-189493">bones</a> and <a href="https://physicsworld.com/a/archaeological-dating-by-re-firing-ancient-pots/">pottery</a>.</p>
<p>Using this method, scientists have determined that the oldest known meteorite is <a href="https://doi.org/10.1073/pnas.2026129118">4.57 billion years old</a>, almost identical to the Sun’s asteroseismology measurement of 4.58 billion years. The oldest known rocks on Earth have slightly younger ages of <a href="https://doi.org/10.1038/35051550">4.40 billion years</a>.
Similarly, soil brought back from the Moon during the Apollo missions had <a href="https://doi.org/10.1016/0012-821X(70)90093-2">radionuclide ages of up to 4.6 billion years</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up image of craters on the surface of the moon." src="https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Craters on the moon’s surface.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/mondoberfl%C3%A4che-royalty-free-image/1174421451?phrase=crater+moon&adppopup=true">Tomekbudujedomek/Moment via Getty Images</a></span>
</figcaption>
</figure>
<p>Although studying radionuclides is a powerful method for measuring the ages of planets, it usually requires having a rock in hand. Typically, astronomers only have a picture of a planet to go by. Astronomers often determine the ages of rocky space objects like Mars or the Moon by <a href="https://en.wikipedia.org/wiki/Crater_counting#:%7E:text=Crater%20counting%20is%20a%20method,rate%20that%20is%20assumed%20known.">counting their craters</a>. Older surfaces have more craters than younger surfaces. However, erosion from water, wind, <a href="https://phys.org/news/2021-09-cosmic-rays-erode-largest-interstellar.html">cosmic rays</a> and lava flow from volcanoes can wipe away evidence of earlier impacts.</p>
<p>Aging techniques don’t work for giant planets like Jupiter that have deeply buried surfaces. However, astronomers can estimate their ages by <a href="https://doi.org/10.1016/j.icarus.2020.114184">counting craters on their moons</a> or studying the <a href="https://doi.org/10.1073/pnas.1704461114">distribution of certain classes of meteorites</a> scattered by them, which are consistent with radionuclide and cratering methods for rocky planets.</p>
<p>We cannot yet directly measure the ages of planets outside our solar system with current technology.</p>
<h2>How accurate are these estimates?</h2>
<p>Our own solar system provides the best check for accuracy, since astronomers can compare the radionuclide ages of rocks on the Earth, Moon, or asteroids to the asteroseismology age of the Sun, and these match very well. </p>
<p>Stars in clusters like the <a href="https://en.wikipedia.org/wiki/Pleiades">Pleiades</a> or <a href="https://en.wikipedia.org/wiki/Omega_Centauri">Omega Centauri</a> are believed to have all formed at roughly the same time, so age estimates for individual stars in these clusters should be the same. In some stars, <a href="https://ui.adsabs.harvard.edu/abs/2023ApJ...948..122S/abstract">astronomers can detect</a> radionuclides like uranium – a heavy metal found in rocks and soil – in their atmospheres, which have been used to check the ages from other methods. </p>
<p>Astronomers believe planets are roughly the same age as their host stars, so improving methods to determine a star’s age helps determine a planet’s age as well. By studying subtle clues, it’s possible to make an educated guess of the age of an otherwise steadfast star.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/205809/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Burgasser receives funding from NASA and the National Science Foundation.</span></em></p>Measuring the ages of planets and stars is tricky. An observational astrophysicist describes the subtle clues that provide good estimates for how old different space objects are.Adam Burgasser, Professor of Astronomy & Astrophysics, University of California, San DiegoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2107682023-08-21T12:24:46Z2023-08-21T12:24:46ZCaroline Herschel was England’s first female professional astronomer, but still lacks name recognition two centuries later<figure><img src="https://images.theconversation.com/files/543255/original/file-20230817-13660-rbgibr.jpg?ixlib=rb-1.1.0&rect=65%2C133%2C1998%2C1572&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Herschel Museum in Bath, England, has a new display of a handwritten draft of Caroline Herschel’s memoirs.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:The_Juvenile_instructor_(1866)_(14577404920).jpg">Internet Archive Book Images via Wikimedia Commons</a></span></figcaption></figure><p><a href="https://www.britannica.com/biography/Caroline-Lucretia-Herschel">Caroline Herschel</a>, the <a href="https://www.researchgate.net/publication/259930283_The_Hidden_Giants">first English professional female astronomer</a>, made contributions to astronomy that are still important to the field today. But even many astronomers may not recognize her name.</p>
<p>Most scientists care about the newest techniques, data and theories in their field, but they often know very little about the history of their discipline. <a href="https://scholar.google.com/citations?user=5CChghwAAAAJ&hl=en">Astronomers, like me,</a> are no exception.</p>
<p>It wasn’t until I taught an intro to astronomy class that I learned about Caroline. Now, thanks to a new display of her papers <a href="https://herschelmuseum.org.uk/">at the Herschel Museum</a> in Bath, England, others will get to learn about her too. Her story reflects not only the priorities of astronomy but also how credit is assigned in the field.</p>
<h2>Her path to astronomy</h2>
<p>Caroline Herschel, born in 1750, did not have an easy childhood. After a bout with typhus left her scarred at a young age, her family assumed that she would never marry and <a href="https://www.penguinrandomhouse.com/books/82017/the-age-of-wonder-by-richard-holmes/">treated her as an unpaid servant</a>. She was forced to complete household chores, despite showing a keen interest in learning from a young age. She eventually escaped her family to follow her older brother <a href="https://www.britannica.com/biography/William-Herschel">William Herschel</a>, whom she adored, to Bath.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/542891/original/file-20230815-25-k6lyuy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration of two people, and man and a woman, leaning over a table. The man polishes a lens on the table. Other astronomical instruments are visible behind them." src="https://images.theconversation.com/files/542891/original/file-20230815-25-k6lyuy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542891/original/file-20230815-25-k6lyuy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=870&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542891/original/file-20230815-25-k6lyuy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=870&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542891/original/file-20230815-25-k6lyuy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=870&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542891/original/file-20230815-25-k6lyuy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1094&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542891/original/file-20230815-25-k6lyuy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1094&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542891/original/file-20230815-25-k6lyuy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1094&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Caroline Herschel worked with her brother William on many pursuits.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/c/c3/Sir_William_Herschel_and_Caroline_Herschel._Wellcome_V0002731_%28cropped%29.jpg">A. Diethe/Wellcome Images via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Caroline was a somewhat unwilling astronomer at first. She didn’t become interested in astronomy until William was already thoroughly engrossed in the subject. Although <a href="https://doi.org/10.1038/013361a0">she spoke somewhat disparagingly</a> about how she followed her brother to different interests, including music and astronomy, Caroline <a href="https://doi.org/10.1038/013361a0">eventually acknowledged</a> her real interest in studying astronomical bodies.</p>
<p>Astronomers at the time were mainly interested in <a href="https://www.britannica.com/science/astronomy/Herschel-and-the-Milky-Way">finding new objects and mapping out the heavens</a> with precision. Using telescopes to look for new comets and nebulae was also popular. William Herschel became famous after his <a href="https://doi.org/10.1098/rstl.1781.0056">discovery of Uranus in 1781</a>, though he mistook the planet for a comet at first.</p>
<p>At the beginning of her career, Caroline worked as William’s assistant. She focused mostly on <a href="https://www.penguinrandomhouse.com/books/82017/the-age-of-wonder-by-richard-holmes/">astronomical instrumentation tasks</a>, like polishing telescope mirrors. She also <a href="https://press.princeton.edu/books/hardcover/9780691148335/discoverers-of-the-universe">helped copy catalogs and took careful notes</a> about William’s observations. But then she began to make her own observations.</p>
<h2>Searching the skies</h2>
<p>In 1782, Caroline began recording the positions of new objects in her own logbook. It was through this work that <a href="https://doi.org/10.48550/arXiv.1212.0809">she discovered several comets and nebulae</a>. On Aug. 1, 1782, <a href="https://doi.org/10.1098/rstl.1787.0001">she discovered a comet</a> – meaning she was the first to see it in a telescope with her own eyes. This was the <a href="https://herschelmuseum.org.uk/wp-content/uploads/2022/12/Herschel-Museum-buys-Caroline-Herschels-memoirs-FINAL.pdf">first comet discovery attributed to a woman</a>. She went on to <a href="https://www.britannica.com/biography/Caroline-Lucretia-Herschel">discover seven more comets</a> over the next 11 years.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/543257/original/file-20230817-7412-iuf5bh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A black and white portrait of an older lady wearing a ruffled bonnet, pointing at a paper. She's holding a magnifying glass." src="https://images.theconversation.com/files/543257/original/file-20230817-7412-iuf5bh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/543257/original/file-20230817-7412-iuf5bh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=768&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543257/original/file-20230817-7412-iuf5bh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=768&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543257/original/file-20230817-7412-iuf5bh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=768&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543257/original/file-20230817-7412-iuf5bh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=965&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543257/original/file-20230817-7412-iuf5bh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=965&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543257/original/file-20230817-7412-iuf5bh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=965&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Caroline Herschel (1750−1848) was the first woman to receive a salary as a scientist.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:ETH-BIB-Herschel,_Caroline_(1750-1848)-Portrait-Portr_11026-092-SF.jpg">ETH Library via Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>At the time of the Herschels’ work, it was the actual observation of an object that warranted public recognition, so Caroline was given credit only for the comets she saw through the telescope herself. For all of her other work, like recording and organizing all the data from William’s observations, she received less credit than William.</p>
<p>For instance, when Caroline took all of William’s observations and compiled them into a catalog, it was <a href="https://www.jstor.org/stable/41df1d85-a112-3847-84fe-5f10debf1250?seq=18">published under William’s name</a>. Caroline is mentioned only as an “assistant” in the paper.</p>
<p>Nonetheless, in recognition of her discoveries and her work as William’s assistant, King George III of England <a href="https://www.penguinrandomhouse.com/books/82017/the-age-of-wonder-by-richard-holmes/">granted Caroline a salary</a>, making her the first professional female astronomer. </p>
<p>Later in life, Caroline reorganized the same catalog in a more efficient way, according to how practicing astronomers interested in looking for comets <a href="https://press.princeton.edu/books/hardcover/9780691148335/discoverers-of-the-universe">actually observed the night sky</a>. This updated catalog was later used as the basis of the <a href="https://ui.adsabs.harvard.edu/abs/1888MmRAS..49....1D/abstract">New General Catalogue</a>, which <a href="https://doi.org/10.3847/2041-8213/aa91c9">astronomers still</a> <a href="https://www.nytimes.com/2017/10/16/science/ligo-neutron-stars-collision.html">use today</a> to organize the stars.</p>
<p>The Herschels also created the first – though not quite correct – <a href="https://doi.org/10.1098/rstl.1785.0012">map of our galaxy, the Milky Way</a>.</p>
<h2>Who gets the credit in astronomy?</h2>
<p>Recognition for scientific work within the astronomical community is pretty different now than it was in the Herschels’ day. In fact, most of the astronomers who receive credit today are those whose work looks a lot like Caroline’s – recording and organizing data about astronomical observations. </p>
<p>Astronomers seldom put their eyeballs up to a telescope eyepiece anymore, and many of the most important discoveries are made by <a href="https://theconversation.com/james-webb-space-telescope-an-astronomer-on-the-team-explains-how-to-send-a-giant-telescope-to-space-and-why-167516">telescopes in space</a>. But astronomers still need to be able to make sense of all the data from these telescopes. Catalogs like the ones Caroline made are important tools for doing so. </p>
<p>Most people today haven’t heard of Caroline Herschel. Despite having several astronomical objects – and <a href="https://mailchi.mp/ace3dfcbde8a/dedicated_launch">even a satellite</a> – <a href="https://doi.org/10.1007/978-3-540-29925-7_282">named after her</a>, she doesn’t have the same name recognition as the other astronomers of her time. Some of the lack of recognition is probably because her brother received all the credit for her catalog. Today, astronomers would give them both credit.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/543270/original/file-20230817-17-oq5i48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Photograph of a cluster of stars" src="https://images.theconversation.com/files/543270/original/file-20230817-17-oq5i48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/543270/original/file-20230817-17-oq5i48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543270/original/file-20230817-17-oq5i48.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543270/original/file-20230817-17-oq5i48.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543270/original/file-20230817-17-oq5i48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543270/original/file-20230817-17-oq5i48.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543270/original/file-20230817-17-oq5i48.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The cluster of stars NGC 7789 is unofficially nicknamed ‘Caroline’s Rose’ in honor of Caroline Herschel.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Caroline%27s_Rose_Open_Cluster_(NGC7789).jpg">Anton Vakulenko via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Herschel is just one in a long line of female astronomers who did not receive the credit they were due and whose work was used to justify prizes for male scientists instead. These issues aren’t just restricted to 18th-century science, but persist through modern astronomy as well. <a href="https://www.britannica.com/biography/Jocelyn-Bell-Burnell">Jocelyn Bell Burnell</a>, who discovered the first radio pulsar, was <a href="https://www.nature.com/articles/d41586-018-06210-w">left off the 1974 Nobel Prize</a>, and the award was <a href="https://theconversation.com/should-all-nobel-prizes-be-canceled-for-a-year-97996">instead granted to her Ph.D. adviser</a>. </p>
<p>Although astronomy has come a long way since the 18th century, astronomers still need to think carefully about how to fairly recognize the people who participate in scientific discoveries. Acknowledging the contributions of astronomers like Caroline Herschel is a small step toward giving credit where credit is due.</p>
<p><em>This article has been updated to acknowledge other women astronomers who preceded Herschel.</em></p><img src="https://counter.theconversation.com/content/210768/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kris Pardo does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Astronomer Caroline Herschel’s work discovering and cataloging astronomical objects in the 18th century is still used in the field today, but she didn’t always get her due credit.Kris Pardo, Assistant Professor of Physics and Astronomy, USC Dornsife College of Letters, Arts and SciencesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2088482023-08-15T20:02:57Z2023-08-15T20:02:57ZCurious Kids: how do black holes pull in light?<figure><img src="https://images.theconversation.com/files/541440/original/file-20230807-25-zu9lzr.jpg?ixlib=rb-1.1.0&rect=68%2C85%2C5623%2C3421&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/black-hole-disk-glowing-plasma-supermassive-1720186741">Shutterstock</a></span></figcaption></figure><blockquote>
<p>How can a black hole pull in light when light isn’t a physical thing? – Will, age 8, Victoria</p>
</blockquote>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>What an excellent question, Will! I too wondered about this when I started to learn the wonders of physics.</p>
<p>To answer this, we must first explain three things: 1) what is light, 2) what is gravity, and 3) what is a black hole? </p>
<h2>1) What is light?</h2>
<p>Light is just a type of energy, travelling through space. There are many different types of light we can’t physically see, but can detect and even use. For example, ultraviolet light that comes from our Sun is why you have to wear sunscreen – so the light doesn’t hurt your skin.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541443/original/file-20230807-17-eqraxl.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart showing the entire electromagnetic spectrum from radio waves to gamma rays" src="https://images.theconversation.com/files/541443/original/file-20230807-17-eqraxl.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541443/original/file-20230807-17-eqraxl.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=251&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541443/original/file-20230807-17-eqraxl.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=251&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541443/original/file-20230807-17-eqraxl.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=251&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541443/original/file-20230807-17-eqraxl.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=315&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541443/original/file-20230807-17-eqraxl.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=315&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541443/original/file-20230807-17-eqraxl.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=315&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The electromagnetic spectrum includes all types of electromagnetic radiation – that is, energy. The bit in the middle with a rainbow and a sun symbol on it marks visible light.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-can-our-brains-sense-electromagnetic-waves-209267">Curious Kids: can our brains sense electromagnetic waves?</a>
</strong>
</em>
</p>
<hr>
<p>It’s important for us to remember that just because light doesn’t have mass, it still is very much a physical thing in our universe, following physical laws.</p>
<p>The neat thing is, no matter what type of light, it all follows the <em>same</em> physical laws in the universe. One rule is that light always wants to travel in a straight line through space.</p>
<p>This is where we now need to break down gravity, and what space is made of. </p>
<h2>2) What is gravity?</h2>
<p>Gravity is the force that keeps us safe here on Earth. It also keeps Earth circling around (orbiting) our Sun. But what causes gravity?</p>
<p>Many scientists in history pondered this question, and came up with all sorts of theories. But when Albert Einstein presented his theory on general relativity in 1915, we started to really understand exactly what gravity was, and how it affects our universe. </p>
<p>Einstein had mathematically worked out that we exist in something called “spacetime”. You can picture this as the fabric of our universe. Like a fabric, it can bend and stretch. I like to picture space like a trampoline. When you put something heavy (like a bowling ball) in the middle of a trampoline, the fabric underneath it bends and sinks down. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/540366/original/file-20230801-24-ijcskj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A cartoon image of a purple trampoline with a bowling ball in the middle" src="https://images.theconversation.com/files/540366/original/file-20230801-24-ijcskj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/540366/original/file-20230801-24-ijcskj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=310&fit=crop&dpr=1 600w, https://images.theconversation.com/files/540366/original/file-20230801-24-ijcskj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=310&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/540366/original/file-20230801-24-ijcskj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=310&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/540366/original/file-20230801-24-ijcskj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=389&fit=crop&dpr=1 754w, https://images.theconversation.com/files/540366/original/file-20230801-24-ijcskj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=389&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/540366/original/file-20230801-24-ijcskj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=389&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A trampoline being bent by a bowling ball is not unlike spacetime being bent by something heavy. This is how gravity works.</span>
<span class="attribution"><span class="source">Sara Webb</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Now imagine a universe-sized trampoline, and we place our Sun on it. The dip in that trampoline represents the gravity of the Sun. And we can do this with every object that has mass.</p>
<p>When spacetime is bent by that mass, the lines that would normally be straight become slightly curved – you can see that in the picture below. This is most extreme around the really massive objects we call black holes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/540368/original/file-20230801-17-s9g6ur.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart showing a grid lightly stretched by a yellow ball, and very stretched by a black ball" src="https://images.theconversation.com/files/540368/original/file-20230801-17-s9g6ur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/540368/original/file-20230801-17-s9g6ur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=660&fit=crop&dpr=1 600w, https://images.theconversation.com/files/540368/original/file-20230801-17-s9g6ur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=660&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/540368/original/file-20230801-17-s9g6ur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=660&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/540368/original/file-20230801-17-s9g6ur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=829&fit=crop&dpr=1 754w, https://images.theconversation.com/files/540368/original/file-20230801-17-s9g6ur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=829&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/540368/original/file-20230801-17-s9g6ur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=829&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Spacetime bending around the Sun compared to a black hole. Note the lines that once would have been straight are bent and curved under the gravity.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Deepening_gravity_well.png">Sara Webb/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-are-planets-created-200454">Curious Kids: How are planets created?</a>
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</em>
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<h2>3) What is a black hole?</h2>
<p>Black holes are, in my opinion, one of the coolest things we’ve ever discovered in the universe. Black holes are regions of space so dense, nothing can escape.</p>
<p>They are usually formed when very large stars get too heavy and collapse (implode) on themselves. Astronomers think all the mass in the black hole is actually squished into a single point in the middle.</p>
<p>Black holes get a bad reputation for eating “anything that is near them”, which is just not true. Black holes do have a distance from their centre, which we mark as the point of no return. This is called the event horizon.</p>
<p>But farther away from this point, light and matter can circle around a black hole for a very long time. </p>
<h2>So how can a black hole pull in light?</h2>
<p>Now we’ve broken down those three key things, we can answer the great question asked by Will: how can a black hole pull in light? </p>
<p>When light is travelling near a black hole, it is still trying to travel in a straight line. As it gets closer to the black hole where spacetime is bent, the light will follow those bends.</p>
<p>When light gets <em>very close</em> to the black hole, it can be trapped circling around and around it. That’s because the fabric of spacetime is bent to the extreme. As you’ll remember, light is indeed a physical thing and is affected by spacetime.</p>
<p>Possibly my favourite part about this fact is it doesn’t just apply to black holes.</p>
<p>Anything with enough mass can make light bend around it, even our Sun. This was how scientists first confirmed Einstein’s theory of gravity <a href="https://www.discovermagazine.com/the-sciences/how-the-1919-solar-eclipse-made-einstein-the-worlds-most-famous-scientist">was likely correct in 1919</a>.</p>
<p>Something really heavy, like a whole group of galaxies clumped together, can bend space so much, it works like a magnifying glass and <a href="https://esahubble.org/wordbank/gravitational-lensing">shows zoomed-in pictures</a> of the stars behind it.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-are-gravitational-waves-190830">Curious Kids: what are gravitational waves?</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/208848/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sara Webb does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Black holes are known for pulling in all kinds of stuff – including light. Here’s how that actually works.Sara Webb, Postdoctoral Research Fellow, Centre for Astrophysics and Supercomputing, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2078302023-07-13T20:05:32Z2023-07-13T20:05:32ZWe’ve detected a star barely hotter than a pizza oven – the coldest ever found to emit radio waves<figure><img src="https://images.theconversation.com/files/534486/original/file-20230628-29-v7zc7u.png?ixlib=rb-1.1.0&rect=673%2C3%2C1365%2C1015&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/LSR_J1835%2B3259#/media/File:Powerful_Auroras_Found_at_Brown_Dwarf_(19641761103).jpg, https://www.pexels.com/photo/stars-1257860/">Composite: Chuck Carter / Gregg Hallinan (Caltech) and Philippe Donn (Pexels)</a></span></figcaption></figure><p>We have identified the coldest star ever found to produce radio waves – a brown dwarf too small to be a regular star and too massive to be a planet.</p>
<p>Our findings, published today in the <a href="https://iopscience.iop.org/article/10.3847/2041-8213/ace188">Astrophysical Journal Letters</a>, detail the detection of pulsed radio emission from this star, called WISE J0623.</p>
<p>Despite being roughly the same size as Jupiter, this dwarf star has a magnetic field much more powerful than our Sun’s. It’s joining the ranks of just a small handful of known ultra-cool dwarfs that generate repeating radio bursts.</p>
<h2>Making waves with radio stars</h2>
<p>With over 100 billion stars in our Milky Way galaxy, it might surprise you astronomers have detected radio waves from fewer than 1,000 of them. One reason is because radio waves and optical light are generated by different physical processes.</p>
<p>Unlike the thermal (heat) radiation coming from the hot outer layer of a star, radio emission is the result of particles called electrons speeding up and interacting with magnetised gas around the star.</p>
<p>Because of this we can use the radio emission to learn about the atmospheres and magnetic fields of stars, which ultimately could tell us more about the potential for life to survive on any planets that orbit them. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-webb-telescope-has-released-its-very-first-exoplanet-image-heres-what-we-can-learn-from-it-189876">The Webb telescope has released its very first exoplanet image – here's what we can learn from it</a>
</strong>
</em>
</p>
<hr>
<p>Another factor is the sensitivity of radio telescopes which, historically, could only detect sources that were very bright. </p>
<p>Most of the detections of stars with radio telescopes over the past few decades have been flares from highly active stars or energetic bursts from the interaction of binary (two) star systems. But with the improved sensitivity and coverage of new radio telescopes, we can detect less luminous stars such as cool <a href="https://astronomy.swin.edu.au/cosmos/B/brown+dwarf">brown dwarfs</a>.</p>
<figure class="align-center ">
<img alt="Images of star, brown dwarfs and planets comparing their masses." src="https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532586/original/file-20230619-23-l44kho.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mass comparison of stars, brown dwarfs and planets (not to scale).</span>
<span class="attribution"><span class="source">NASA/JPL-Caltech</span></span>
</figcaption>
</figure>
<p>WISE J0623 has a temperature of around 700 Kelvin. That’s equivalent to 420°C or about the same temperature as a commercial pizza oven – pretty hot by human standards, but quite cold for a star.</p>
<p>These cool brown dwarfs can’t sustain the levels of atmospheric activity that generates radio emission in hotter stars, making stars like WISE J0623 harder for radio astronomers to find.</p>
<h2>How did we find the coolest radio star?</h2>
<p>This is where the new <a href="https://www.csiro.au/askap">Australian SKA Pathfinder</a> radio telescope comes in. This is located at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory in Western Australia, and has an array of 36 antennas, each 12 metres in diameter.</p>
<p>The telescope can see large regions of the sky in a single observation and has already surveyed nearly 90% of it. From this survey we have identified close to three million radio sources, most of which are <a href="https://theconversation.com/some-black-holes-are-anything-but-black-and-weve-found-more-than-75-000-of-the-brightest-ones-169938">active galactic nuclei</a> – black holes at the centres of distant galaxies.</p>
<p>So how do we tell which of these millions of sources are radio stars? One way is to look for something called “circularly polarised radio emission”.</p>
<p><iframe id="tc-infographic-881" class="tc-infographic" height="400px" src="https://cdn.theconversation.com/infographics/881/69a906363dc78254a227172888b6ecc69ffa3723/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Radio waves, like other electromagnetic radiation, oscillate as they move through space. Circular polarisation occurs when the electric field of the wave rotates in a spiralling or corkscrew motion as it propagates.</p>
<p>For our search we used the fact that the only astronomical objects known to emit a significant fraction of circularly polarised light are stars and <a href="https://theconversation.com/weve-used-a-new-technique-to-discover-the-brightest-radio-pulsar-outside-our-own-galaxy-180508">pulsars</a> (rotating neutron stars).</p>
<p>By selecting only highly circularly polarised radio sources from <a href="https://theconversation.com/weve-mapped-a-million-previously-undiscovered-galaxies-beyond-the-milky-way-take-the-virtual-tour-here-148442">an earlier survey of the sky</a>, we found WISE J0623. You can see using the slider in the figure above that once you switch to polarised light, there is only one object visible.</p>
<h2>What does this discovery mean?</h2>
<p>Was the radio emission from this star some rare one-off event that happened during our 15 minute observation? Or could we detect it again?</p>
<p><a href="https://ui.adsabs.harvard.edu/abs/2008ApJ...684..644H">Previous research</a> has shown that radio emission detected from other cool brown dwarfs was tied to their magnetic fields and generally repeated at the same rate as the star rotates.</p>
<p>To investigate this we did follow-up observations with CSIRO’s <a href="https://www.csiro.au/en/about/facilities-collections/atnf/australia-telescope-compact-array">Australian Telescope Compact Array</a>, and with the <a href="https://www.sarao.ac.za/science/meerkat/">MeerKAT</a> telescope operated by the South African Radio Astronomy Observatory.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=519&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=519&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=519&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=652&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=652&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532595/original/file-20230619-17-n1mp6a.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=652&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The bottom panel shows the brightness of polarised light over time. The top panel shows emission at different radio frequencies.</span>
<span class="attribution"><span class="source">Author Provided.</span></span>
</figcaption>
</figure>
<p>These new observations showed that every 1.9 hours there were two bright, circularly polarised bursts from WISE J0623 followed by a half an hour delay before the next pair of bursts.</p>
<p>WISE J0623 is the coolest brown dwarf detected via radio waves and is the first case of persistent radio pulsations. Using this same search method, we expect future surveys to detect even cooler brown dwarfs.</p>
<p>Studying these missing link dwarf stars will help improve our understanding of stellar evolution and how giant exoplanets (planets in other solar systems) develop magnetic fields.</p>
<hr>
<p><em>We acknowledge the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site where Australian SKA Pathfinder is located, and the Gomeroi people as the traditional owners of the Australian Telescope Compact Array site.</em></p><img src="https://counter.theconversation.com/content/207830/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tara Murphy works for the University of Sydney and receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Kovi Rose does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Astronomers have detected the coldest star ever found to emit radio waves using the Australian SKA Pathfinder telescope.Kovi Rose, Astrophysics PhD Candidate, University of SydneyTara Murphy, Professor, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2071332023-06-07T18:36:02Z2023-06-07T18:36:02ZBrightest cosmic explosion of all time: how we may have solved the mystery of its puzzling persistence<figure><img src="https://images.theconversation.com/files/530418/original/file-20230606-17-8pwe5c.jpg?ixlib=rb-1.1.0&rect=54%2C38%2C2101%2C2117&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An x-ray of the brightest ever gamma ray burst reflected off dust layers, creating extended 'light echoes' of the initial blast. </span> <span class="attribution"><span class="source">Nasa</span></span></figcaption></figure><p>First <a href="https://www.darpa.mil/about-us/timeline/vela">detected accidentally</a> by US military satellites in the late 1960s, cosmic explosions known as gamma ray bursts (GRBs) have come to be understood as the brightest explosions in the universe.</p>
<p>Typically, they <a href="https://www.space.com/gamma-ray-burst.html">are the result</a> of the cataclysmic birth of a black hole in a distant galaxy. One way this can happen is through the collapse of a single, massive star.</p>
<p>Astronomers such as myself working in the field are well aware of the massive energy scales involved in GRBs. We know they can release as much energy in gamma rays as the Sun does throughout its lifetime. But every once in a while, an event is observed that still gives us pause.</p>
<p>In October 2022, gamma-ray detectors on the orbital satellites Fermi and the Neil Gehrels Swift Observatory <a href="https://science.nasa.gov/grb-221009a">noted a burst</a> known as GRB 221009A (the date of detection). </p>
<p>This quickly turned out to be a record-setter. It was dubbed the Brightest Of All Time, or the “Boat”, as convenient shorthand among astronomers studying and observing the event. Not only did the Boat start out bright, it refused to fade away like other bursts.</p>
<p>We still do not fully know why the burst was so exceptionally bright, but our new study, <a href="http://www.science.org/doi/10.1126/sciadv.adi1405">published in Science Advances</a>, provides an answer for its stubborn persistence. </p>
<p>The burst originated from a distance of 2.4 billion light years – relatively nearby for a GRB. But even when accounting for relative distance, the energy of the event and the radiation produced by its aftermath were off the charts. It is decidedly not normal for a cosmically distant event to deposit about a gigawatt of power into the Earth’s upper atmosphere.</p>
<h2>Observing narrow cosmic jets of gas</h2>
<p>GRBs such as the Boat launch a stream of gas moving at very close to light speed into space. How exactly the jet is launched remains something of a puzzle – but most likely, it involves magnetic fields near where the black hole is being formed. </p>
<p>It is the early emission from this jet that we see as the burst. Later, the jet slows down and produces additional radiation, a fading afterglow of light – from radio waves up to (in exceptional cases) gamma rays.</p>
<p>We do not observe jets directly. Instead, like distant stars, we see GRBs as points in the sky. Nevertheless, we have good reason to believe that GRBs do not explode in all directions equally. For GRB 221009A, this would certainly be unreasonable, as it would involve multiplying the amount of energy detected on Earth by all other directions – amounting to much more energy than any star would have available.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/nwZSO6ULI2o?wmode=transparent&start=2" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Another indication that GRBs come from jets pointing roughly at us is due to special relativity theory. Relativity teaches us that the speed of light is constant, no matter how fast a source moves at us. But that still allows for the <em>direction</em> of light to become distorted. Thanks to this fun-house mirror effect, light emitted in all directions from the surface of a fast-moving jet will end up focused strongly along its direction of motion. </p>
<p>That said, the edges of a jet heading in our direction will be very slightly curved away, meaning their light is focused away from our direction. Only later, when the jet slows down, do the edges normally come into view and does the afterglow start to fade faster.</p>
<p>But here again, GRB 221009A broke the rules. Its edges never showed, and it joined a select group of very bright bursts that refuse to fade normally. Rather than starting to fade slowly and then disappearing quickly, it is steadily fading over time. </p>
<p>In our work, we demonstrate how the appearance of the jet edges can be obscured in a way that matches the observations of the Boat. The key idea is as follows: yes, a narrow jet was launched, but it had a difficult time escaping the collapsing star, leading to a lot of mixing with stellar gas along the sides of the jet.</p>
<h2>From simulation to observation</h2>
<p>To test whether this was indeed the case, we took <a href="https://academic.oup.com/mnras/article/500/3/3511/5974546">a computer simulation result</a> showing this mixing and implemented it in a model that could actually be compared to the Boat data directly. And it showed that what would normally be a quick turnover to a strongly fading signal, now became a drawn-out affair. </p>
<p>Radiation from the dying star’s shock-heated gas kept appearing in our line of sight, explaining why it stayed so bright. This kept happening all the way up to the point that any characteristic jet signature was lost in the overall emission. </p>
<p>This way, GRB 221009A not only confirms expectations from simulation, but also provides a clue to similarly bright events seen in the past, where people had to keep <a href="https://academic.oup.com/mnras/article/462/1/1111/2589937">revising the energy estimate upwards</a> while waiting for a jet edge to show. </p>
<p>We calculated that the likelihood of seeing a burst this bright is about one in a thousand years, so we are lucky to have spotted one. But questions remain. What role do magnetic fields play, for example?</p>
<p>Theorists and numerical modellers will be exploring these matters for years, scouring the Boat data while we stay on the lookout for the next big event to arrive</p><img src="https://counter.theconversation.com/content/207133/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hendrik Van Eerten receives funding from the UK's Science and Technology Facilities Council (STFC) and from the European Research Council (ERC).</span></em></p>Radiation from the brightest cosmic explosion ever seen may have been mixing with gas and dust around its dying star – making the signal last longer.Hendrik Van Eerten, Reader in Astrophysics, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2052652023-05-10T12:28:10Z2023-05-10T12:28:10ZAstronomers just saw a star eat a planet – an astrophysicist on the team explains the first-of-its-kind discovery<figure><img src="https://images.theconversation.com/files/525217/original/file-20230509-17-8m0pr7.jpg?ixlib=rb-1.1.0&rect=0%2C137%2C3460%2C2017&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New research shows that the destructive merging of a star and a planet expels huge amounts of gas, as shown in this artist's impression.</span> <span class="attribution"><a class="source" href="https://www.nature.com/articles/d41586-023-01385-3">K. Miller/R. Hurt (Caltech/IPAC)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>For the first time, astronomers have captured images that show a star consuming one of its planets. The star, named ZTF SLRN-2020, is located in the Milky Way galaxy, in the constellation Aquila. As the star swallowed its planet, the star brightened to 100 times its normal level, allowing the 26-person team of astronomers I worked with to <a href="https://doi.org/10.1038/s41586-023-05842-x">detect this event as it happened</a>.</p>
<p><a href="https://itc.cfa.harvard.edu/people/morgan-macleod">I am a theoretical astrophysicist</a>, and I developed the computer models that our team uses to interpret the data we collect from telescopes. Although we only see the effects on the star, not the planet directly, our team is confident that the event we witnessed was a star swallowing its planet. Witnessing such an event for the first time has confirmed the long-standing assumption that stars swallow their planets and has illuminated how this fascinating process plays out.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A white domed building at sunset." src="https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524944/original/file-20230508-247807-drmefx.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Zwicky Transient Facility in Southern California is one of the observatories that captured the flash of light caused by the star consuming its planet.</span>
<span class="attribution"><a class="source" href="https://www.ztf.caltech.edu/multimedia.html#">Caltech/Palomar</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Finding a flash in the dynamic night sky</h2>
<p>The team I work with searches for the bursts of light and gas that occur when two stars merge into a bigger, single star. To do this, we have been using data from the <a href="https://www.ztf.caltech.edu/">Zwicky Transient Facility</a>, a telescope located on Palomar Mountain in Southern California. It takes nightly images of broad swaths of the sky, and astronomers can then compare these images to find stars that change in brightness over time, or what are called astronomical transients.</p>
<p>Finding stars that change in brightness isn’t the challenge – it’s sorting out the cause behind any specific change to a star. As my colleague <a href="https://space.mit.edu/people/de-kishalay/">Kishalay De</a> likes to say, “There are plenty of things in the sky that go boom.” The trick to identifying stellar mergers is to combine visible light – like the data collected at Palomar – with infrared data from <a href="https://www.nasa.gov/mission_pages/WISE/main/index.html">NASA’s WISE space telescope</a>, which has been surveying the entire sky for the past decade.</p>
<p>In 2020, the star ZTF SLRN-2020 suddenly became 100 times brighter in visible light over just 10 days. It then slowly started to fade back toward its normal brightness. About nine months before, the same object started to emit a lot of infrared light, too. This is exactly what it looks like when two stars merge together, with one critical difference – everything was scaled down. The brightness and total energy of this event were about a thousand times lower than any of the merging stellar pairs astronomers had found to date. </p>
<h2>When a star swallows its planets</h2>
<p>The idea that stars could engulf some of their planets has been a long-standing assumption in astronomy. Astronomers have long known that when stars <a href="https://www.teachastronomy.com/textbook/Star-Birth-and-Death/Nuclear-Reactions-in-Main-Sequence-Stars/">run out of hydrogen in their cores</a>, they get brighter and begin to <a href="https://www.teachastronomy.com/textbook/Star-Birth-and-Death/Red-Giants/">increase in size</a>.</p>
<p>Many planets have orbits that are <a href="https://doi.org/10.5281/zenodo.6368226">smaller than the eventual size of their parent stars</a>. So, when a star runs out of fuel and starts to expand, the planets nearby are inevitably consumed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A graph showing two lines increasing to a peak near the same time with one increasing over a much shorter period of time." src="https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=305&fit=crop&dpr=1 600w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=305&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=305&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=383&fit=crop&dpr=1 754w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=383&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/525243/original/file-20230509-43918-15gi7w.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=383&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The star ZTF SLRN-2020 increased in brightness in both visible and infrared wavelengths of light, with the peak occurring on May 24, 2020.</span>
<span class="attribution"><span class="source">M. MacLeod</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Interpreting a stellar flash</h2>
<p>In the ZTF SLRN-2020 outburst, our team never saw the planet itself, only the brightening from when the star absorbed the planet. This is where combining theoretical models with the observational data allowed us to understand what the telescopes captured.</p>
<p>The merging of two stars into a single, bigger star is a <a href="https://doi.org/10.3847/1538-4357/835/2/282">dramatic event</a> that throws matter out into the stars’ surroundings. A large part of my career has focused on <a href="https://doi.org/10.3847/1538-4357/aacf08">modeling the way stellar gas moves</a> and crashes into itself and is expelled in these moments of intense interaction. </p>
<p>My work has shown that the total mass of matter ejected in a merging event is proportional to the <a href="https://doi.org/10.3847/1538-4357/ab89b6">size of the objects involved in the merger</a>. Merge two equally large stars and you see a huge disturbance. Merge one star with a much smaller companion and the event might throw out a tiny fraction of the total mass of the stars.</p>
<p>The energy released during ZTF SLRN-2020’s outburst was a thousand times lower than typical for a two-star merger. This implies that the object that merged with the star weighed a thousand times less than a normal star. This clue pointed our team toward a gas giant planet – like Jupiter in our own solar system, which weighs roughly a thousand times less than the Sun.</p>
<p>Compared to Jupiter, however, this planet must have <a href="https://doi.org/10.48550/arXiv.2210.15848">orbited much closer to the star</a>, with one revolution around the star only taking a few days. <a href="https://doi.org/10.1146/annurev-astro-082214-122246">About 1% of stars</a> share this configuration of a large planet orbiting incredibly close to its parent star. </p>
<p>Further, I think that this configuration of a big planet close to its star is important in generating the event our team saw. My past research suggests that smaller planets – or ones in more-distant orbits that only get consumed once a star has grown massively in size – might be <a href="https://doi.org/10.3847/2041-8213/aaa5fa">swallowed without a detectable flash</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/nDi0JIRDXI0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The planet around ZTF SLRN-2020 skimmed the stellar surface before eventually falling into the star.</span></figcaption>
</figure>
<h2>Learning from the real thing</h2>
<p>From our data and modeling for ZTF SLRN-2020, our team has been able to paint a much clearer picture of how stars and planets merge. First, the planet skims across the surface of the star for many years, slowly heating up and expelling material <a href="https://doi.org/10.1038/d41586-023-01385-3">from the star’s atmosphere</a>. As this gas expands and cools, some of it forms molecules and dust. This cloud of dust gives the star a progressively redder color and emits increasing amounts of infrared radiation.</p>
<p>In the case of ZTF SLRN-2020, the orbit of the planet shrank slowly at first, then faster and faster as the planet smashed through the denser layers of the star’s atmosphere. Eventually, in just a few final days, the planet plunged below the surface of the star and was torn apart by the heat and force of the collision. This rapid injection of energy supplied heat to power ZTF SLRN-2020’s 10-day, hundredfold increase in brightness. Following this climactic moment, the star began to fade, telling our team that the planet-swallowing process was over and that the star was beginning to go back to business as usual. </p>
<p>While the destructive event has passed, there is still much to be learned. Next week our team will start analyzing data from the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a> in the hopes of learning about the chemistry of the gas that now surrounds ZTF SLRN-2020.</p><img src="https://counter.theconversation.com/content/205265/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Morgan MacLeod is grateful for support from the Clay Postdoctoral Fellowship at the Smithsonian Astrophysical Observatory and from the National Science Foundation. </span></em></p>Stars begin to expand when they run out of fuel and can become thousands of times larger, consuming any planets in the way. For the first time, astronomers have witnessed one such event.Morgan MacLeod, Postdoctoral Fellow in Theoretical Astrophysics, Harvard UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2038192023-05-03T12:11:10Z2023-05-03T12:11:10ZMay 5, 2023, lunar eclipse will be a subtle show of astronomical wonder<figure><img src="https://images.theconversation.com/files/523890/original/file-20230502-16-holf94.jpg?ixlib=rb-1.1.0&rect=7%2C32%2C2381%2C973&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Penumbral lunar eclipses slightly darken the Moon.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Penumbral_Lunar_Eclipse_2020-01-10.jpg#/media/File:Penumbral_Lunar_Eclipse_2020-01-10.jpg">H. Raab/Wikipedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>On May 5, 2023, people around the world will <a href="https://eclipse.gsfc.nasa.gov/LEdecade/LEdecade2021.html">witness a a lunar eclipse</a> when the Earth gets between the Sun and the Moon and casts part of its shadow on the Moon.</p>
<p>The eclipse will be visible in Africa, Asia, Australia and large portions of Europe, though not in the U.S. this time around. This eclipse is not what some call a “blood moon,” as it will not turn red. Instead, the Moon will dim slightly as it passes through a <a href="https://earthsky.org/astronomy-essentials/what-is-a-penumbral-eclipse-of-the-moon/">lighter part of the Earth’s shadow</a> – called the penumbra.</p>
<p>I am the <a href="https://www.abramsplanetarium.org/Staff/Index.html">director of the Abrams Planetarium</a> at Michigan State University and it is part of my job to get people outside and looking up, and eclipses are some of the easiest to see. While the upcoming event will not be the most stunning celestial display, it is just the first of a number of eclipses occurring over the next year, and they all work in similar ways.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the orientation of a lunar eclipse." src="https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/522228/original/file-20230420-16-7nm8zk.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A lunar eclipse occurs when the Moon passes through the Earth’s shadow.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Geometry_of_a_Lunar_Eclipse.svg#/media/File:Geometry_of_a_Lunar_Eclipse.svg">Sagredo/Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>How do eclipses work?</h2>
<p>Both lunar and solar eclipses depend on particular orientations of the Earth, Sun and Moon. A lunar eclipse occurs when the Earth’s shadow covers all or part of the Moon. This can only happen when the Moon is directly on the opposite side of the Earth from Sun, which is also when full moons occur.</p>
<p>Like the Earth, half of the Moon is illuminated by the Sun at any one time. When the Moon and the Sun are perfectly opposite each other, people on Earth can see the entire lit-up side, which looks like a round disc in the night sky.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing how orientations of the Moon correspond to phases of the Moon." src="https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=183&fit=crop&dpr=1 600w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=183&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=183&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=230&fit=crop&dpr=1 754w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=230&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/522227/original/file-20230420-24-zy1cng.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=230&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Lunar eclipses can only occur during a full moon when the Moon is opposite the Sun.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Fases_lunars.png#/media/File:Moon_phases_en.jpg">Orion 8/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>If the Moon had a totally flat orbit, every full moon would be a lunar eclipse. But the Moon’s orbit is tilted by about 5 degrees relative to Earth’s orbit of the Sun. Because of this small tilt, most of the time a full moon ends up a little above or below the shadow cast by the Earth.</p>
<p>But twice in each monthlong lunar orbit, the Moon crosses through the same horizontal plane as the Earth and the Sun. If this happens during a full moon, the Sun, Earth and Moon will form a straight line and the Moon will pass through the Earth’s shadow, resulting in a lunar eclipse.</p>
<h2>The Earth’s shadow</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A circular shadow on a wall with a dark center and lighter ring around it." src="https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=558&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=558&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523892/original/file-20230502-1446-ty2lbe.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=558&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The shadow on the wall has a darker center surrounded by a lighter, but still shadowed, outer ring, just like the shadow cast by Earth.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Shadow_Blister_Effect.png#/media/File:Shadow_Blister_Effect.png">User4288/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>As the Sun shines light on Earth, Earth casts a shadow behind itself. But the darkness of shadows are not always uniform, and the shadow cast by the Earth is no exception. </p>
<p>The rays of light coming from a wide, or extended, light source – such as the Sun or a flashlight – don’t all come from the exact same location. Since the Sun is large, there can be quite a distance between the origin of rays of light heading toward Earth. </p>
<p>This difference in location means that when Earth blocks the light coming from one part of the Sun, it might not block out light coming from another location on the Sun. This results in <a href="http://www.differencebetween.net/science/difference-between-penumbra-and-umbra/">parts of Earth’s shadow that are darker</a> – the darkest part is where all light is blocked, while the lighter parts are because some light still makes it past the Earth.</p>
<p>A total lunar eclipse is when the Moon passes entirely through the darkest part, or umbra, of the Earth’s shadow. A partial lunar eclipse is when the umbra covers part of the Moon. The eclipse on May 5, 2023, is the last kind of eclipse where only the lighter part of the shadow will cover the Moon, which is why it is known as a penumbral lunar eclipse.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A map showing regions of Earth where people can see the lunar eclipse." src="https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=264&fit=crop&dpr=1 600w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=264&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=264&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=332&fit=crop&dpr=1 754w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=332&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/522231/original/file-20230420-1202-8eu7lo.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=332&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The lunar eclipse on May 5, 2023, will be visible for most of Africa, Asia, Europe and Australia.</span>
<span class="attribution"><a class="source" href="https://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2023May05N.pdf">NASA</a></span>
</figcaption>
</figure>
<h2>How can you see the lunar eclipse?</h2>
<p>As long as you are on the night side of the Earth when a lunar eclipse happens, you can see it. The May 5 penumbral eclipse will be visible in most of Europe and Africa at moonrise, Asia and Australia will be able to see the entirety of the event in the middle of the night, and locations throughout the Pacific Ocean will be able to see it at moonset. </p>
<p>Lunar eclipses are relatively short, only lasting a few hours from start to finish. Totality, the part of the eclipse that is darkest, lasts about 30 to 60 minutes depending on how close to the center of the shadow you are. </p>
<p>For people in North and South America where the eclipse won’t be visible, there will be <a href="https://eclipse.gsfc.nasa.gov/LEdecade/LEdecade2021.html">plenty more in the next few years</a>. The next lunar eclipse will be Oct. 28, 2023, and will be a partial eclipse visible primarily in Africa, Europe and Asia. But the Americas will have their own penumbral eclipse on March 25, 2024, followed by a partial lunar eclipse on Sep. 18, 2024. </p>
<p>For those hoping to catch the next total lunar eclipse, they will have to wait until March 14, 2025, when a total lunar eclipse will be visible from the Americas, western Europe and western Africa.</p><img src="https://counter.theconversation.com/content/203819/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shannon Schmoll does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Not all lunar eclipses are alike. An astronomer explains the science behind the slight dimming of the Moon on May 5, 2023.Shannon Schmoll, Director of the Abrams Planetarium, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2043512023-05-03T12:10:32Z2023-05-03T12:10:32ZAI is helping astronomers make new discoveries and learn about the universe faster than ever before<figure><img src="https://images.theconversation.com/files/523645/original/file-20230501-18-4e90m3.jpg?ixlib=rb-1.1.0&rect=0%2C299%2C4895%2C3031&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The sky is big and full of information that AI tools can help astronomers unlock. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/paul-wild-observatory-under-starry-sky-royalty-free-image/637273906?phrase=telescope+with+milky+way&adppopup=true">Yuga Kurita/Moment via Getty Images</a></span></figcaption></figure><p>The famous first image of a black hole <a href="https://doi.org/10.3847/2041-8213/acc32d">just got two times sharper</a>. A research team used artificial intelligence to dramatically improve upon <a href="https://doi.org/10.3847/2041-8213/ab0ec7">its first image</a> from 2019, which now shows the black hole at the center of the M87 galaxy as darker and bigger than the first image depicted.</p>
<p>I’m an <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">astronomer</a> who studies and has written about <a href="https://wwnorton.com/books/9780393343861">cosmology</a>, <a href="https://wwnorton.com/books/9780393357509">black holes</a> and <a href="https://www.penguinrandomhouse.com/books/718149/worlds-without-end-by-chris-impey/">exoplanets</a>. Astronomers have been using AI for decades. In fact, in 1990, astronomers from the University of Arizona, where I am a professor, were among the <a href="https://www.datasciencecentral.com/the-evolution-of-astronomical-ai/">first to use a type of AI called a neural network</a> to study the shapes of galaxies. </p>
<p>Since then, AI has spread into every field of astronomy. As the technology has become more powerful, AI algorithms have begun helping astronomers tame massive data sets and discover new knowledge about the universe.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/523641/original/file-20230501-18-3sjj1h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A group of radio antennas pointed at the sky." src="https://images.theconversation.com/files/523641/original/file-20230501-18-3sjj1h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523641/original/file-20230501-18-3sjj1h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523641/original/file-20230501-18-3sjj1h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523641/original/file-20230501-18-3sjj1h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523641/original/file-20230501-18-3sjj1h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523641/original/file-20230501-18-3sjj1h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523641/original/file-20230501-18-3sjj1h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Astronomy is no longer limited to just optical images – radio telescopes produce huge amounts of data that researchers need to process.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/observatory-antenna-in-the-sunse-royalty-free-image/1309400138?phrase=astronomy+data&adppopup=true">Wenbin/Moment via Getty Images</a></span>
</figcaption>
</figure>
<h2>Better telescopes, more data</h2>
<p>As long as astronomy has been a science, it has involved trying to make sense of the multitude of objects in the night sky. That was relatively simple when the only tools were the naked eye or a simple telescope, and all that could be seen were a few thousand stars and a handful of planets.</p>
<p>A hundred years ago, Edwin Hubble used newly built telescopes to show that the universe is filled with not just stars and clouds of gas, <a href="https://www.nasa.gov/content/about-story-edwin-hubble">but countless galaxies</a>. As telescopes have continued to improve, the sheer number of celestial objects humans can see and the <a href="https://events.asiaa.sinica.edu.tw/school/20170904/talk/djorgovski1.pdf">amount of data</a> astronomers need to sort through have both grown exponentially, too.</p>
<p>For example, the soon-to-be-completed <a href="https://www.lsst.org/about">Vera Rubin Observatory</a> in Chile will make images so large that it would take 1,500 high-definition TV screens to view each one in its entirety. Over 10 years it is expected to generate 0.5 exabytes of data – about 50,000 times the amount of information held in all of the books contained within the Library of Congress. </p>
<p>There are 20 telescopes with mirrors larger than 20 feet (6 meters) in diameter. AI algorithms are the only way astronomers could ever hope to work through all of the data available to them today. There are a number of ways AI is proving useful in processing this data.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/523642/original/file-20230501-292-iuhviz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A sky filled with galaxies." src="https://images.theconversation.com/files/523642/original/file-20230501-292-iuhviz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523642/original/file-20230501-292-iuhviz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523642/original/file-20230501-292-iuhviz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523642/original/file-20230501-292-iuhviz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523642/original/file-20230501-292-iuhviz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523642/original/file-20230501-292-iuhviz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523642/original/file-20230501-292-iuhviz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">One of the earliest uses of AI in astronomy was to pick out the multitude of faint galaxies hidden in the background of images.</span>
<span class="attribution"><a class="source" href="https://flickr.com/photos/nasawebbtelescope/52777397541/">ESA/Webb, NASA & CSA, J. Rigby</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Picking out patterns</h2>
<p>Astronomy often involves looking for needles in a haystack. About 99% of the pixels in an astronomical image contain background radiation, light from other sources or the blackness of space – only 1% have the subtle shapes of faint galaxies. </p>
<p>AI algorithms – in particular, neural networks that use many interconnected nodes and are able to learn to recognize patterns – are perfectly suited for picking out the patterns of galaxies. Astronomers began <a href="https://doi.org/10.1111/j.1365-2966.2010.16713.x">using neural networks to classify galaxies</a> in the early 2010s. Now the algorithms <a href="https://www.nao.ac.jp/en/news/science/2020/20200811-subaru.html">are so effective</a> that they can classify galaxies with an accuracy of 98%.</p>
<p>This story has been repeated in other areas of astronomy. Astronomers working on SETI, the Search for Extraterrestrial Intelligence, use radio telescopes to look for signals from distant civilizations. Early on, radio astronomers scanned charts by eye to <a href="https://earthsky.org/space/wow-signal-explained-comets-antonio-paris/">look for anomalies</a> that couldn’t be explained. More recently, researchers harnessed 150,000 personal computers and 1.8 million citizen scientists to look for artificial <a href="https://www.nytimes.com/2020/03/23/science/seti-at-home-aliens.html">radio signals</a>. Now, researchers are using AI to sift through reams of data much more quickly and thoroughly than people can. This has allowed SETI efforts to cover more ground while also greatly reducing the <a href="https://doi.org/10.1038/s41550-022-01872-z">number of false positive signals</a>.</p>
<p>Another example is the search for exoplanets. Astronomers discovered most of the <a href="https://exoplanets.nasa.gov/">5,300 known exoplanets</a> by measuring a dip in the amount of light coming from a star <a href="https://exoplanets.nasa.gov/resources/2338/exoplanet-detection-transit-method/">when a planet passes in front of it</a>. AI tools can now pick out the signs of an exoplanet with <a href="https://doi.org/10.48550/arXiv.2011.14135">96% accuracy</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/523643/original/file-20230501-16-xeiogk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A planet near a dim red star." src="https://images.theconversation.com/files/523643/original/file-20230501-16-xeiogk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523643/original/file-20230501-16-xeiogk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523643/original/file-20230501-16-xeiogk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523643/original/file-20230501-16-xeiogk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523643/original/file-20230501-16-xeiogk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523643/original/file-20230501-16-xeiogk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523643/original/file-20230501-16-xeiogk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">AI tools can help astronomers discover new exoplanets like TRAPPIST-1 b.</span>
<span class="attribution"><a class="source" href="https://flickr.com/photos/nasawebbtelescope/52775409328/">NASA, ESA, CSA, Joseph Olmsted (STScI)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Making new discoveries</h2>
<p>AI has proved itself to be excellent at identifying known objects – like galaxies or exoplanets – that astronomers tell it to look for. But it is also quite powerful at finding objects or phenomena that are theorized but have not yet been discovered in the real world.</p>
<p>Teams have used this approach to detect <a href="https://www.sciencedaily.com/releases/2023/02/230207144222.htm">new exoplanets</a>, learn about the <a href="https://www.quantamagazine.org/with-ai-astronomers-dig-up-the-stars-that-birthed-the-milky-way-20230328/">ancestral stars</a> that led to the formation and growth of the Milky Way, and predict the signatures of new types of <a href="https://cerncourier.com/a/gravitational-wave-astronomy-turns-to-ai/">gravitational waves</a>.</p>
<p>To do this, astronomers first use AI to convert theoretical models into observational signatures – including realistic levels of noise. They then use machine learning to sharpen the ability of AI to detect the predicted phenomena.</p>
<p>Finally, radio astronomers have also been using AI algorithms to sift through signals that don’t correspond to known phenomena. Recently a team from South Africa found a <a href="https://www.biznews.com/global-citizen/2023/04/06/machine-learnings-discovery-astronomy">unique object</a> that may be a remnant of the explosive merging of two supermassive black holes. If this proves to be true, the data will allow a new test of general relativity – Albert Einstein’s <a href="https://theconversation.com/why-does-gravity-pull-us-down-and-not-up-162141">description of space-time</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/523644/original/file-20230501-22-dihfie.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two side-by-side images of an orange circular haze around a dark center." src="https://images.theconversation.com/files/523644/original/file-20230501-22-dihfie.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523644/original/file-20230501-22-dihfie.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=301&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523644/original/file-20230501-22-dihfie.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=301&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523644/original/file-20230501-22-dihfie.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=301&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523644/original/file-20230501-22-dihfie.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=378&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523644/original/file-20230501-22-dihfie.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=378&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523644/original/file-20230501-22-dihfie.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=378&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The team that first imaged a black hole, at left, used AI to generate a sharper version of the image, at right, showing the black hole to be larger than originally thought.</span>
<span class="attribution"><a class="source" href="https://iopscience.iop.org/article/10.3847/1538-4357/acaa9a/meta">Medeiros et al 2023</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Making predictions and plugging holes</h2>
<p>As in many areas of life recently, generative AI and large language models like ChatGPT are also making waves in the astronomy world.</p>
<p>The team that created the first image of a black hole in 2019 used a <a href="https://doi.org/10.3847/2041-8213/acc32d">generative AI to produce its new image</a>. To do so, it first taught an AI how to recognize black holes by feeding it simulations of many kinds of black holes. Then, the team used the AI model it had built to fill in gaps in the massive amount of data collected by the radio telescopes on the black hole M87. </p>
<p>Using this simulated data, the team was able to create a new image that is two times sharper than the original and is fully consistent with the predictions of general relativity.</p>
<p>Astronomers are also turning to AI to help tame the complexity of modern research. A team from the Harvard-Smithsonian Center for Astrophysics created a <a href="https://doi.org/10.48550/arXiv.2212.00744">language model called astroBERT</a> to read and organize 15 million scientific papers on astronomy. Another team, based at NASA, has even proposed using AI to <a href="https://www.technologyreview.com/2021/09/20/1035890/ai-predict-astro2020-decadal-survey/">prioritize astronomy projects</a>, a process that astronomers engage in every 10 years.</p>
<p>As AI has progressed, it has become an essential tool for astronomers. As telescopes get better, as data sets get larger and as AIs continue to improve, it is likely that this technology will play a central role in future discoveries about the universe.</p><img src="https://counter.theconversation.com/content/204351/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation and Epic Games.</span></em></p>Artificial intelligence tools are making waves in almost every aspect of life, and astronomy is no different. An astronomer explains the history and future of AI in understanding the universe.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2016222023-03-16T12:36:48Z2023-03-16T12:36:48ZWater in space – a ‘Goldilocks’ star reveals previously hidden step in how water gets to planets like Earth<figure><img src="https://images.theconversation.com/files/515568/original/file-20230315-1821-gn9l6v.jpg?ixlib=rb-1.1.0&rect=28%2C45%2C1249%2C1038&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The star system V883 Orionis contains a rare star surrounded by a disk of gas, ice and dust.</span> <span class="attribution"><a class="source" href="http://www.eso.org/public/images/eso1626a/">A. Angelich (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Without water, life on Earth could not exist as it does today. Understanding the history of water in the universe is critical to understanding how planets like Earth come to be.</p>
<p>Astronomers typically refer to the journey water takes from its formation as individual molecules in space to its resting place on the surfaces of planets as “the water trail.” The trail starts in the interstellar medium with hydrogen and oxygen gas and ends with oceans and ice caps on planets, with icy moons orbiting gas giants and icy comets and asteroids that orbit stars. The beginnings and ends of this trail are easy to see, but the middle has remained a mystery.</p>
<p><a href="https://www.cv.nrao.edu/%7Ejtobin/">I am an astronomer</a> who studies the formation of stars and planets using observations from radio and infrared telescopes. In a new paper, my colleagues and I describe the <a href="https://www.nature.com/articles/s41586-022-05676-z">first measurements ever made</a> of this previously hidden middle part of the water trail and what these findings mean for the water found on planets like Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="The progression of a star system from a cloud of dust and gas into a mature star with orbiting planets." src="https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515526/original/file-20230315-18-7eqg1b.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Star and planet formation is an intertwined process that starts with a cloud of molecules in space.</span>
<span class="attribution"><a class="source" href="https://www.nrao.edu/pr/2012/clumpcores/">Bill Saxton, NRAO/AUI/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>How planets are formed</h2>
<p>The formation of stars and planets is intertwined. The so-called “emptiness of space” – or the interstellar medium – in fact contains <a href="https://doi.org/10.1146/annurev.aa.32.090194.001203">large amounts of gaseous hydrogen</a>, smaller amounts of other gasses and <a href="https://doi.org/10.1086/162480">grains of dust</a>. Due to gravity, some pockets of the interstellar medium will become <a href="https://doi.org/10.1086/311687">more dense as particles attract each other</a> and form clouds. As the density of these clouds increases, atoms begin to collide more frequently and <a href="https://doi.org/10.1086/381775">form larger molecules</a>, including water that forms <a href="https://doi.org/10.1080/0144235X.2015.1046679">on dust grains and coats the dust in ice</a>.</p>
<p>Stars begin to form when parts of the collapsing cloud reach a certain density and heat up enough to start fusing hydrogen atoms together. Since only a small fraction of the gas initially collapses into the newborn protostar, the rest of the gas and dust <a href="https://doi.org/10.48550/arXiv.1001.1404">forms a flattened disk of material</a> circling around the spinning, newborn star. Astronomers call this a proto-planetary disk.</p>
<p>As icy dust particles collide with each other inside a proto-planetary disk, <a href="https://doi.org/10.1051/0004-6361/200811158">they begin to clump together</a>. The process continues and eventually forms the familiar objects of space like asteroids, comets, rocky planets like Earth and gas giants like Jupiter or Saturn.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A cloudy filament against a backdrop of stars." src="https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=679&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=679&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=679&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=854&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=854&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515633/original/file-20230315-3008-q4peeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=854&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gas and dust can condense into clouds, like the Taurus Molecular Cloud, where collisions between hydrogen and oxygen can form water.</span>
<span class="attribution"><a class="source" href="http://www.eso.org/public/images/eso1209a/">ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Two theories for the source of water</h2>
<p>There are two potential pathways that water in our solar system could have taken. The first, called <a href="https://doi.org/10.1051/0004-6361/200810846">chemical inheritance</a>, is when the water molecules originally formed in the interstellar medium are delivered to proto-planetary disks and all the bodies they create without going through any changes. </p>
<p>The second theory is called <a href="https://doi.org/10.1051/0004-6361/201628509">chemical reset</a>. In this process, the heat from the formation of the proto-planetary disk and newborn star breaks apart water molecules, which then reform once the proto-planetary disk cools.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Models of protium and deuterium." src="https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515531/original/file-20230315-26-gk368.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Normal hydrogen, or protium, does not contain a neutron in its nucleus, while deuterium contains one neutron, making it heavier.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Hydrogen_Deuterium_Tritium_Nuclei_Schmatic-en.svg">Dirk Hünniger/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>To test these theories, astronomers like me look at the ratio between normal water and a special kind of water called semi-heavy water. Water is normally made of two hydrogen atoms and one oxygen atom. Semi-heavy water is made of one oxygen atom, one hydrogen atom and one atom of deuterium – a heavier isotope of hydrogen with an extra neutron in its nucleus. </p>
<p>The ratio of semi-heavy to normal water is a guiding light on the water trail – measuring the ratio can tell astronomers a lot about the source of water. <a href="https://doi.org/10.1051/0004-6361/202039084">Chemical models</a> and <a href="https://doi.org/10.1086/591506">experiments</a> have shown that about 1,000 times more semi-heavy water will be produced in the cold interstellar medium <a href="https://doi.org/10.1126/science.1258055">than in the conditions of a protoplanetary disk</a>. </p>
<p>This difference means that by measuring the ratio of semi-heavy to normal water in a place, astronomers can tell whether that water went through the chemical inheritance or chemical reset pathway.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A star surrounded by a ring of gas and dust." src="https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515533/original/file-20230315-1689-gn9l6v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">V883 Orionis is a young star system with a rare star at its center that makes measuring water in the proto-planetary cloud, shown in the cutaway, possible.</span>
<span class="attribution"><a class="source" href="https://public.nrao.edu/news/water-v883-orionis/">ALMA (ESO/NAOJ/NRAO), B. Saxton (NRAO/AUI/NSF)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Measuring water during the formation of a planet</h2>
<p>Comets have a ratio of semi-heavy to normal water almost perfectly in line with <a href="https://doi.org/10.2458/azu_uapress_9780816531240-ch037">chemical inheritance</a>, meaning the water hasn’t undergone a major chemical change since it was first created in space. Earth’s ratio sits somewhere in between the inheritance and reset ratio, making it unclear where the water came from.</p>
<p>To truly determine where the water on planets comes from, astronomers needed to find a goldilocks proto-planetary disk – one that is just the right temperature and size to allow observations of water. Doing so has <a href="https://doi.org/10.1051/0004-6361/201935994">proved to be incredibly difficult</a>. It is possible to detect semi-heavy and normal water when water is a gas; unfortunately for astronomers, the vast majority of proto-plantary disks are very cold and <a href="https://doi.org/10.1126/science.1239560">contain mostly ice</a>, and it is nearly <a href="https://doi.org/10.1051/0004-6361:20031277">impossible to measure water ratios</a> from ice at interstellar distances. </p>
<p>A breakthrough came in 2016, when my colleagues and I were studying proto-planetary disks around a rare type of young star called FU Orionis stars. Most young stars consume matter from the proto-planetary disks around them. FU Orionis stars are unique because they consume matter about 100 times faster than typical young stars and, as a result, <a href="https://doi.org/10.1146/annurev-astro-081915-023347">emit hundreds of times more energy</a>. Due to this higher energy output, the proto-planetary disks around FU Orionis stars are heated to much higher temperatures, turning ice into water vapor out to large distances from the star.</p>
<p>Using the <a href="https://public.nrao.edu/telescopes/alma/">Atacama Large Millimeter/submillimeter Array</a>, a powerful radio telescope in northern Chile, <a href="https://ui.adsabs.harvard.edu/abs/2016Natur.535..258C/abstract">we discovered</a> a large, warm proto-planetary disk around the Sunlike young star V883 Ori, about 1,300 light years from Earth in the constellation Orion.</p>
<p>V883 Ori emits 200 times more energy than the Sun, and my colleagues and I recognized that it was an ideal candidate to observe the semi-heavy to normal water ratio. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A radio image of the disk around V883 Ori." src="https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=672&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=672&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=672&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=844&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=844&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515565/original/file-20230315-14-dfl7h6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=844&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The proto-planetary disk around V883 Ori contains gaseous water, shown in the orange layer, allowing astronomers to measure the ratio of semi-heavy to normal water.</span>
<span class="attribution"><a class="source" href="https://public.nrao.edu/news/water-v883-orionis/#PRimage2">ALMA (ESO/NAOJ/NRAO), J. Tobin, B. Saxton (NRAO/AUI/NSF)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Completing the water trail</h2>
<p>In 2021, the Atacama Large Millimeter/submillimeter Array took measurements of V883 Ori for six hours. The data revealed a <a href="https://doi.org/10.1038/s41586-022-05676-z">strong signature of semi-heavy and normal water</a> coming from V883 Ori’s proto-planetary disk. We measured the ratio of semi-heavy to normal water and found that the ratio was very <a href="https://doi.org/10.1051/0004-6361/202039084">similar to ratios found in comets</a> as well as the ratios found <a href="https://doi.org/10.1051/0004-6361/201322845">in younger protostar systems</a>.</p>
<p>These results fill in the gap of the water trail forging a direct link between water in the interstellar medium, protostars, proto-planetary disks and planets like Earth through the process of inheritance, not chemical reset.</p>
<p>The new results show definitively that a substantial portion of the water on Earth most likely formed billions of years ago, before the Sun had even ignited. Confirming this missing piece of water’s path through the universe offers clues to origins of water on Earth. Scientists have previously suggested that most water on Earth <a href="https://doi.org/10.1051/0004-6361/201935554">came from comets impacting the planet</a>. The fact that Earth has less semi-heavy water than comets and V883 Ori, but more than chemical reset theory would produce, means that water on Earth likely came from more than one source.</p><img src="https://counter.theconversation.com/content/201622/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Tobin receives funding from NASA, </span></em></p>Astronomers have long known where water is first formed in the universe and how it ends up on planets, asteroids and comets. A recent discovery has finally answered what happens in between.John Tobin, Scientist, National Radio Astronomy ObservatoryLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1982742023-03-08T13:41:07Z2023-03-08T13:41:07ZDistant star TOI-700 has two potentially habitable planets orbiting it – making it an excellent candidate in the search for life<figure><img src="https://images.theconversation.com/files/512978/original/file-20230301-18-2jg7dp.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1859%2C1034&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The TOI-700 star system is home to four planets, including two in its habitable zone that could host liquid water.</span> <span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/images/largesize/PIA23408_hires.jpg">NASA's Goddard Space Flight Center</a></span></figcaption></figure><p>NASA recently announced the <a href="https://doi.org/10.3847/2041-8213/acb599">discovery of a new, Earth-sized planet</a> in the habitable zone of a nearby star called TOI-700. <a href="https://sites.google.com/site/josepherodriguezjr/">We are</a> <a href="https://avanderburg.github.io/">two of</a> the astronomers who led the discovery of this planet, called TOI-700 e. TOI-700 e is just over 100 light years from Earth – too far away for humans to visit – but we do know that it is similar in size to the Earth, likely rocky in composition and could potentially support life.</p>
<p>You’ve probably heard about some of the <a href="https://exoplanets.nasa.gov/trappist1/">many</a> <a href="https://www.eso.org/public/news/eso1629/">other</a> <a href="https://www.nasa.gov/press-release/nasa-kepler-mission-discovers-bigger-older-cousin-to-earth">exoplanet</a> <a href="https://www.nasa.gov/image-feature/kepler-1649c-earth-size-habitable-zone-planet-hides-in-plain-sight">discoveries</a> in <a href="https://www.nasa.gov/mission_pages/kepler/news/kepscicon-briefing.html">recent</a> years. In fact, TOI-700 e is one of two potentially habitable planets just in the TOI-700 star system. </p>
<p>Habitable planets are those that are just the right distance from their star to have a surface temperature that could sustain liquid water. While it is always exciting to find a new, potentially habitable planet far from Earth, the focus of exoplanet research is shifting away from simply discovering more planets. Instead, researchers are focusing their efforts on finding and studying systems most likely to answer key questions about how planets form, how they evolve, and whether life might exist in the universe. TOI-700 e stands out from many of these other planet discoveries because it is well suited for future studies that could help answer big question about the conditions for life outside the solar system. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/xNeRqbw18Jk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Specific methods for detecting exoplanets, like the transit method, which looks for a dip in the light coming from a distant star as a planet passes in front of it, have led to an explosion in the number of known exoplanets.</span></figcaption>
</figure>
<h2>From 1 to 5,000</h2>
<p>Astronomers discovered the first exoplanet around a Sun-like star <a href="https://doi.org/10.1038/378355a0">in 1995</a>. The field of exoplanet discovery and research has been rapidly evolving ever since.</p>
<p>At first, astronomers were finding only a <a href="https://www.hughosborn.co.uk/2015/02/09/a-history-of-planet-detection-in-one-animation/">few exoplanets each year</a>, but the combination of new cutting-edge facilities focused on <a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite">exoplanet science</a> with improved detection sensitivity have led to astronomers’ discovering hundreds of exoplanets each year. As detection methods and tools have improved, the amount of information scientists can learn about these planets has increased. In 30 years, scientists have gone from barely being able to detect exoplanets to <a href="https://theconversation.com/to-search-for-alien-life-astronomers-will-look-for-clues-in-the-atmospheres-of-distant-planets-and-the-james-webb-space-telescope-just-proved-its-possible-to-do-so-184828">characterizing key chemical clues in their atmospheres</a>, like water, using facilities like the James Webb Space Telescope.</p>
<p>Today, there are more than <a href="https://exoplanetarchive.ipac.caltech.edu/">5,000 known exoplanets</a>, ranging from gas giants to small rocky worlds. And perhaps most excitingly, astronomers have now found about a dozen exoplanets that are likely rocky and orbiting within the habitable zones of their respective stars.</p>
<p>Astronomers have even discovered a few systems – like TOI-700 – that have more than one planet orbiting in the habitable zone of their star. We call these keystone systems.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a star with a green ring around it marking the habitable zone." src="https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=185&fit=crop&dpr=1 600w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=185&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=185&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=233&fit=crop&dpr=1 754w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=233&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/512975/original/file-20230301-24-8pqinb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=233&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The TOI-700 system has a large habitable zone, and the newly discovered TOI-700 e, not shown in this image, orbits the star along the inner edge of the habitable zone.</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/spaceimages/images/largesize/PIA23407_hires.jpg">NASA's Goddard Space Flight Center</a></span>
</figcaption>
</figure>
<h2>A pair of habitable siblings</h2>
<p>TOI-700 first made headlines when our team announced the discovery of <a href="https://doi.org/10.3847/1538-3881/aba4b2">three small planets orbiting the star</a> in early 2020. Using a <a href="https://doi.org/10.3847/1538-3881/aba4b3">combination of observations</a> from NASA’s <a href="https://exoplanets.nasa.gov/tess/">Transiting Exoplanet Surveying Satellite</a> mission and the <a href="https://www.nasa.gov/mission_pages/spitzer/main/index.html">Spitzer Space Telescope</a> we discovered these planets by measuring small dips in the amount of light coming from TOI-700. These dips in light are caused by planets passing in front of the small, cool, red dwarf star at the center of the system.</p>
<p>By taking precise measurements of the changes in light, we were able to determine that at least three small planets are in the TOI-700 system, with hints of a possible fourth. We could also determine that the third planet from the star, TOI-700 d, orbits within its star’s habitable zone, where the temperature of the planet’s surface could allow for liquid water. </p>
<p>The Transiting Exoplanet Surveying Satellite observed TOI-700 for another year, from July 2020 through May 2021, and using these observations <a href="https://doi.org/10.3847/2041-8213/acb599">our team found the fourth planet, TOI-700 e</a>. TOI-700 e is 95% the size of the Earth and, much to our surprise, orbits on the inner edge of the star’s habitable zone, between planets c and d. Our discovery of this planet makes TOI-700 one of only a few known systems with two Earth-sized planets orbiting in the habitable zone of their star. The fact that it is relatively close to Earth also makes it one of the most accessible systems in terms of future characterization.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="James Webb Space Telescope against the backdrop of space." src="https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=467&fit=crop&dpr=1 600w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=467&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=467&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/512981/original/file-20230301-24-v7fzr8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=586&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">New tools, like the James Webb Space Telescope, can provide clues about life on distant planets, but with thousands of scientific questions to answer, efficient use of time is key.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:James_Webb_Space_Telescope.jpg#/media/File:James_Webb_Space_Telescope.jpg">Bricktop/Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>The bigger questions and tools to answer them</h2>
<p>With the successful launch of the James Webb Space Telescope, astronomers are now able to start <a href="https://www.nasa.gov/feature/goddard/2022/nasa-s-webb-reveals-an-exoplanet-atmosphere-as-never-seen-before">characterizing the atmospheric chemistry</a> of exoplanets and search for <a href="https://theconversation.com/to-search-for-alien-life-astronomers-will-look-for-clues-in-the-atmospheres-of-distant-planets-and-the-james-webb-space-telescope-just-proved-its-possible-to-do-so-184828">clues about whether life exists</a> on them. In the near future, a number of massive, ground-based telescopes will also help reveal further details about the composition of planets far from the solar system. </p>
<p>But even with powerful new telescopes, collecting enough light to learn these details requires pointing the telescope at a system for a <a href="https://arxiv.org/abs/1708.04239">long period of time</a>. With thousands of <a href="https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-go">valuable scientific questions to answer</a>, astronomers need to know where to look. And that is the goal of our team, to find the most interesting and promising exoplanets to study with the Webb telescope and future facilities.</p>
<p>Earth is currently the only data point in the search for life. It is possible alien life could be vastly different from life as we know it, but for now, places similar to the home of humanity with liquid water on the surface offer a good starting point. We believe that keystone systems with multiple planets that are likely candidates for hosting life – like TOI-700 – offer the best use of observation time. By further studying TOI-700, our team will be able to learn more about what makes a planet habitable, how rocky planets similar to Earth form and evolve, and the mechanisms that shaped the solar system. The more astronomers know about how star systems like TOI-700 and our own solar system work, the better the chances of detecting life out in the cosmos.</p><img src="https://counter.theconversation.com/content/198274/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joseph Rodriguez receives funding from the National Aeronautics and Space Administration and Michigan State University. </span></em></p><p class="fine-print"><em><span>Andrew Vanderburg receives funding from the National Aeronautics and Space Administration and the Massachusetts Institute of Technology. </span></em></p>With more than 5,000 known exoplanets, astronomers are shifting their focus from discovering additional distant worlds to identifying which are good candidates for further study.Joey Rodriguez, Assistant Professor of Physics and Astronomy, Michigan State UniversityAndrew Vanderburg, Assistant Professor of Physics, Massachusetts Institute of Technology (MIT)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1993832023-02-23T13:15:36Z2023-02-23T13:15:36ZNight skies are getting 9.6% brighter every year as light pollution erases stars for everyone<figure><img src="https://images.theconversation.com/files/510410/original/file-20230215-24-phgv5z.jpg?ixlib=rb-1.1.0&rect=747%2C249%2C5060%2C1458&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">All human development, from large cities to small towns, shines light into the night sky. </span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/evobenny/38510489362/">Benny Ang/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/510596/original/file-20230216-18-s7y17h.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/510596/original/file-20230216-18-s7y17h.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/510596/original/file-20230216-18-s7y17h.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=255&fit=crop&dpr=1 600w, https://images.theconversation.com/files/510596/original/file-20230216-18-s7y17h.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=255&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/510596/original/file-20230216-18-s7y17h.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=255&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/510596/original/file-20230216-18-s7y17h.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=321&fit=crop&dpr=1 754w, https://images.theconversation.com/files/510596/original/file-20230216-18-s7y17h.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=321&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/510596/original/file-20230216-18-s7y17h.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=321&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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</figure>
<p>For most of human history, the stars blazed in an otherwise dark night sky. But starting around the Industrial Revolution, as artificial light increasingly lit cities and towns at night, the stars began to disappear.</p>
<p>We are <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en&oi=ao">two</a> <a href="https://noirlab.edu/science/about/scientists-at-noirlab">astronomers</a> who depend on dark night skies to do our research. For decades, astronomers have been <a href="https://about.ifa.hawaii.edu/facility/mauna-kea-observatories/">building telescopes</a> in the <a href="https://www.smithsonianmag.com/travel/star-trekking-chile-astronomy-180955798/">darkest places</a> on Earth to <a href="https://doi.org/10.1007/s00159-010-0032-2">avoid light pollution</a>. </p>
<p>Today, most people live in cities or suburbs that <a href="https://doi.org/10.1038/457027a">needlessly shine light into the sky at night</a>, dramatically reducing the <a href="https://doi.org/10.1126/sciadv.1600377#body-ref-R3">visibility of stars</a>. Satellite data suggests that light pollution over North America and Europe has remained <a href="https://www.science.org/doi/10.1126/sciadv.1701528">constant or has slightly decreased</a> over the last decade, while <a href="https://www.mdpi.com/2072-4292/9/8/798">increasing in other parts of the world</a>, such as Africa, Asia and South America. However, satellites miss the blue light of LEDs, which are <a href="http://dx.doi.org/10.2760/759859">commonly used for outdoor lighting</a> – resulting in an underestimate of light pollution.</p>
<p>An international citizen science project called <a href="https://globeatnight.org">Globe at Night</a> aims to measure how everyday people’s view of the sky is changing.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/510429/original/file-20230215-15-f11qnb.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A number of panels showing different numbers of stars." src="https://images.theconversation.com/files/510429/original/file-20230215-15-f11qnb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/510429/original/file-20230215-15-f11qnb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=540&fit=crop&dpr=1 600w, https://images.theconversation.com/files/510429/original/file-20230215-15-f11qnb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=540&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/510429/original/file-20230215-15-f11qnb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=540&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/510429/original/file-20230215-15-f11qnb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=679&fit=crop&dpr=1 754w, https://images.theconversation.com/files/510429/original/file-20230215-15-f11qnb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=679&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/510429/original/file-20230215-15-f11qnb.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=679&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Globe at Night survey asks users to select which panel – each representing different levels of light pollution – best matches the sky above them.</span>
<span class="attribution"><a class="source" href="https://globeatnight.org/webapp/">The Globe at Night</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Measuring light pollution over time</h2>
<p>Relying on citizen scientists makes it much easier to take multiple measurements of the night sky over time from many different places. </p>
<p>To provide data to the project, volunteers enter the date and time, their location and local weather conditions into an <a href="https://globeatnight.org/webapp/">online reporting page</a> anytime an hour or more after sunset on certain nights each month. The page then shows eight panels, each displaying a constellation visible at that time of year – like Orion in January and February, for example. The first panel, representing a light-polluted night sky, only shows the few brightest stars. Each panel shows progressively more and fainter stars, representing darker and darker skies. The participant then matches what they see in the sky with one of the panels. </p>
<p>The Globe at Night team launched the report page as an online app in 2011, just at the beginning of widespread adoption of LEDs. In <a href="https://doi.org/10.1126/science.abq7781">the recent paper</a>, the team filtered out data points taken during twilight, when the Moon was out, when it was cloudy or when the data was unreliable for any other reason. This left around 51,000 data points, mostly taken in North America and Europe. </p>
<p>The data shows that the night sky got, on average, <a href="https://doi.org/10.1126/science.abq7781">9.6% brighter every year</a>. For many people, the night sky today is twice as bright as it was eight years ago. The brighter the sky, the fewer stars you can see.</p>
<p>If this trend continues, a <a href="https://eos.org/articles/starry-nights-are-disappearing">child born today</a> in a place where 250 stars are visible now would only be able to see 100 stars on their 18th birthday. </p>
<h2>Causes, impacts and solutions</h2>
<p>The main culprits driving increasing brightness of the night sky are urbanization and the growing use of <a href="http://dx.doi.org/10.2760/759859">LEDs for outdoor lighting</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/510413/original/file-20230215-28-33uihp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two pictures of the constellation Orion with one showing many times more stars." src="https://images.theconversation.com/files/510413/original/file-20230215-28-33uihp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/510413/original/file-20230215-28-33uihp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=440&fit=crop&dpr=1 600w, https://images.theconversation.com/files/510413/original/file-20230215-28-33uihp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=440&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/510413/original/file-20230215-28-33uihp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=440&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/510413/original/file-20230215-28-33uihp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=553&fit=crop&dpr=1 754w, https://images.theconversation.com/files/510413/original/file-20230215-28-33uihp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=553&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/510413/original/file-20230215-28-33uihp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=553&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The more light pollution there is, the fewer stars a person can see when looking at the same part of the night sky. The image on the left depicts the constellation Orion in a dark sky, while the image on the right is taken near the city of Orem, Utah, a city of about 100,000 people.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/79297308@N00/3180280752">jpstanley/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The loss of dark skies, both from light pollution and also from <a href="https://doi.org/10.1093/mnrasl/slab030">increasing numbers of satellites orbiting Earth</a>, threatens our ability as astronomers to do <a href="https://doi.org/10.1007/s00159-021-00138-3">good science</a>. But everyday people feel this loss too, as the degradation of dark skies is also a loss of human <a href="https://www.darksky.org/light-pollution/night-sky-heritage/">cultural heritage</a>. Starry night skies have inspired artists, writers, musicians and philosophers for thousands of years. For many, a star-filled sky provides an irreplaceable sense of awe.</p>
<p>Light pollution also interferes with the daily cycle of light and dark that <a href="https://ec.europa.eu/research-and-innovation/en/horizon-magazine/light-pollution-altering-plant-and-animal-behaviour">plants and animals</a> use to regulate sleep, nourishment and reproduction. Two-thirds of the world’s key biodiversity areas are <a href="https://www.upi.com/Science_News/2019/02/11/Light-pollution-affects-most-of-the-planets-key-wildlife-areas/1451549899187">affected by light pollution</a>.</p>
<p>Individuals and their communities can make simple changes to <a href="https://www.darksky.org/light-pollution/light-pollution-solutions/">reduce light pollution</a>. The secret is using the right amount of light, in the right place and at the right time. Shielding outdoor light fixtures so they shine downward, using bulbs that emit more yellow-colored light instead of white light and putting lights on timers or motion sensors can all help reduce light pollution.</p>
<p>The next time you are far away from a major city or another source of light pollution, look up at the night sky. A view of the roughly <a href="https://www.theatlantic.com/technology/archive/2013/11/how-many-stars-are-there-in-the-sky/281641/">2,500 stars you can see with the naked eye</a> in a truly dark sky might convince you that dark skies are a resource worth saving.</p><img src="https://counter.theconversation.com/content/199383/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation and Epic Games.</span></em></p><p class="fine-print"><em><span>Connie Walker works for NSF's NOIRLab and the International Astronomical Union. She is a member of the American Astronomical Society's COMPASSE and on the Board of Directors for the International Dark-Sky Association.</span></em></p>With the help of thousands of citizen scientists, a new study measured exactly how much brighter night skies are getting every year.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaConnie Walker, Scientist, National Optical-Infrared Astronomy Research LaboratoryLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1998312023-02-15T17:16:17Z2023-02-15T17:16:17ZBlack holes may be the source of mysterious dark energy that makes up most of the universe<figure><img src="https://images.theconversation.com/files/509870/original/file-20230213-4443-xsmxpu.jpg?ixlib=rb-1.1.0&rect=313%2C0%2C2251%2C1483&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">black hole</span> </figcaption></figure><p><a href="https://www.nasa.gov/vision/universe/starsgalaxies/black_hole_description.html">Black holes</a> could explain a mysterious form of energy that makes up most of the universe, according to astronomers. The existence of <a href="https://en.wikipedia.org/wiki/Dark_energy">“dark energy”</a> has been inferred from observations of stars and galaxies, but no one has been able to explain what it is, or where it comes from.</p>
<p>The stuff, or matter, that makes up the familiar world around us is just 5% of everything in the universe. Another 27% is <a href="https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy">dark matter</a>, a shadowy counterpart of ordinary matter which does not emit, reflect or absorb light. However, the majority of the cosmos – around 68% – is dark energy.</p>
<p>The new evidence that black holes could be the source of dark energy is described in <a href="https://iopscience.iop.org/article/10.3847/2041-8213/acb704">a scientific paper</a> published in The Astrophysical Journal Letters. The study is the work of 17 astronomers in nine countries and was led by the University of Hawaii. The collaboration included researchers in the UK, based at STFC RAL Space, The Open University, and Imperial College London.</p>
<p>Searching through data spanning nine billion years of cosmic history, the astronomers have uncovered the first evidence of <a href="https://physicsworld.com/a/cosmological-coupling-is-making-black-holes-bigger-study-suggests/">“cosmological coupling”</a>, which would mean that the growth of black holes over time is linked to the expansion of the universe itself.</p>
<p>The idea that black holes might contain something called <a href="https://en.wikipedia.org/wiki/Vacuum_energy">vacuum energy</a> (a manifestation of dark energy) is not particularly new and in fact was discussed theoretically as far back as the 1960s. But this latest work assumes this energy (and therefore the mass of the black holes) would increase with time as the universe expands as a result of cosmological coupling.</p>
<p>The team calculated how much of the dark energy in the universe could be attributed to this process. They found that black holes could potentially explain the total amount of dark energy we measure in the universe today. The result could solve one of the most fundamental problems in modern cosmology.</p>
<h2>Rapid expansion</h2>
<p><a href="https://hubblesite.org/contents/articles/the-big-bang">Our universe began in a Big Bang</a> around 13.7 billion years ago. The energy from this explosion of space and time caused the universe to expand rapidly, with all the galaxies flying away from each other. However, we expect that this expansion would gradually slow down because of the effect of gravity on all the stuff in the cosmos.</p>
<p>This is the version of the universe we thought we lived in until the late 1990s, when the Hubble space telescope discovered something strange. Observations of distant exploding stars showed that, in the past, the universe <a href="https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_universe">was actually expanding more slowly than it is today</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/gjwxnoPoEHQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The new discovery is explained by Chris Pearson of RAL Space and The Open University.</span></figcaption>
</figure>
<p>So the expansion of the universe has not been slowing due to gravity, as everyone thought, but instead has been accelerating. This was highly unexpected and astronomers struggled to explain it.</p>
<p>To account for this, it was proposed that a “dark energy” was responsible for pushing things apart more strongly than gravity pulled things together. The concept of dark energy was very similar to a mathematical construct Einstein had proposed but later discarded – a <a href="https://en.wikipedia.org/wiki/Cosmological_constant">“cosmological constant”</a> that opposed gravity and kept the universe from collapsing.</p>
<h2>Stellar explosions</h2>
<p>But what is dark energy? The solution, it seems, might lie with another cosmic mystery: black holes. Black holes are commonly born when <a href="https://public.nrao.edu/ask/when-does-a-neutron-star-or-black-hole-form-after-a-supernova/">massive stars explode and die at the ends of their lives</a>. The gravity and pressure in these violent explosions compresses vast amounts of material into a small space. For instance, a star about the same mass as our sun would be squashed into a space of just a few tens of kilometres. </p>
<p>A black hole’s gravitational pull is so strong that not even light can escape it – everything gets sucked in. At the centre of the black hole is a place called a <a href="https://bigthink.com/starts-with-a-bang/singularity-black-hole/">singularity</a>, where matter is crushed into a point of infinite density. The problem is that singularities are a mathematical construct that should not exist.</p>
<figure class="align-center ">
<img alt="The Andromeda galaxy" src="https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509866/original/file-20230213-14-3kjqam.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Dark energy explains why the expansion of the universe is speeding up.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/galex/pia15416.html">NASA/JPL-Caltech</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The black holes nestled at the centres of galaxies are much heftier than those born when stars die violently. These galactic “supermassive” black holes can weigh millions to billions of times the mass of our Sun.</p>
<p>All black holes increase in size by accumulating matter, by swallowing stars that get too close, or by merging with other black holes. So we expect them to get bigger as the universe gets older.</p>
<p>In the latest paper, the team looked at supermassive black holes in the centres of galaxies and found that these black holes gain mass over billions of years. </p>
<h2>Radical rethink</h2>
<p>The team compared observations of <a href="https://en.wikipedia.org/wiki/Elliptical_galaxy">elliptical galaxies</a>, which lack star formation, in the past and in the present day. These dead galaxies have used up all their fuel so any increase in their black hole mass over this time cannot be ascribed to the normal processes by which black holes grow by accumulating matter.</p>
<p>Instead, the team proposed that these black holes actually contain vacuum energy and that they are “coupled” to the expansion of the universe, so that they increase in mass as the universe expands. </p>
<figure class="align-center ">
<img alt="Visualisation of a black hole" src="https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&rect=17%2C34%2C3782%2C2098&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509864/original/file-20230213-18-s6s06q.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A visualisation of a black hole, which could play a role in dark energy.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/feature/goddard/2019/nasa-visualization-shows-a-black-hole-s-warped-world">NASA’s Goddard Space Flight Center/Jeremy Schnittman</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>This model neatly provides a possible origin for the dark energy in the universe. It also circumvents the mathematical problems that affect some studies of black holes, because it avoids the need for a singularity at the centre.</p>
<p>The team also calculated how much of the dark energy in the universe could be attributed to this process of coupling. They concluded that it would be possible for black holes to provide the necessary amount of vacuum energy to account for all the dark energy that we measure in the universe today. </p>
<p>This would not only explain the origin of dark energy in the universe but would also make us radically rethink our understanding of black holes and their role in the cosmos.</p>
<p>Much more work needs to be done to test and confirm this idea, both from observations of the sky and from theory. But we may at last be seeing a new way to solve the problem of dark energy.</p><img src="https://counter.theconversation.com/content/199831/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Pearson receives funding from STFC and is head of astronomy at STFC RAL Space and a visiting fellow at the Open University </span></em></p><p class="fine-print"><em><span>Dave Clements receives funding from STFC and the UKSA and works at Imperial College London.</span></em></p>Astronomers have found that mysterious dark energy may originate in black holes.Chris Pearson, Astronomy Group Lead, Space Operations Division at RAL Space, and Visiting Fellow, The Open UniversityDave Clements, Reader in Astrophysics, Imperial College LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1984022023-02-13T13:25:27Z2023-02-13T13:25:27ZWhy does the Earth spin?<figure><img src="https://images.theconversation.com/files/506911/original/file-20230127-14841-6vhvy8.jpg?ixlib=rb-1.1.0&rect=7%2C30%2C5096%2C3356&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">There are many pieces of evidence to help explain why the Earth spins, and some major mysteries.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/students-looking-at-globe-in-classroom-royalty-free-image/142020176">Jose Luis Pelaez Inc/DigitalVision via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why does the Earth spin? Sara H., age 5, New Paltz, New York</strong></p>
</blockquote>
<hr>
<p>A globe was the first thing I ever bought with my own money. I was maybe 5 years old, and I was really excited to take it home. As I quickly discovered, you can spin it in the direction that the earth actually spins.</p>
<p>There’s an imaginary line between the North Pole and the South Pole. We call it the rotation axis. For the Earth, the rotation axis points toward a bright star, Polaris, which is visible on clear nights in the Northern Hemisphere.</p>
<figure class="align-right ">
<img alt="A series of images of Earth seen from a satellite shows the planet rotating through a single day." src="https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506287/original/file-20230125-14-3jz1on.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Satellite images over one day show Earth rotating on its axis.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:EpicEarth-Globespin-tilt-23.4.gif">NASA/EPIC, edit by Tdadamemd</a></span>
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</figure>
<p>If you want to know which way to spin your globe, make the goofy “thumbs-up” sign with your right hand. Imagine your thumb is the Earth’s rotation axis, pointing to the North Pole. Your fingers will naturally curl around your hand, and the direction those fingers are pointing is the way Earth spins.</p>
<p>Every 24 hours, the Earth makes a full rotation, spinning west to east, which is why the sun rises in the east and sets in the west and the stars at night appear to move across the sky.</p>
<p>To understand why this happens, let’s see what we can learn from other bodies in space.</p>
<h2>Everything spins</h2>
<p>The Sun also spins. In fact, it spins in the same direction the Earth does. </p>
<p>Not only that, the Earth orbits the Sun in the same direction, as do all the other planets and more than a million asteroids and dwarf planets.</p>
<p>Most are spinning in the same direction, too. Jupiter and Saturn spin quite a bit faster than Earth, taking only about 10 hours to rotate. Saturn’s spin is a little bit tilted, so we get to <a href="https://en.wikipedia.org/wiki/Saturn#/media/File:Saturnoppositions-animated.gif">see changing views of its rings</a> over time.</p>
<figure class="align-center ">
<img alt="Image of five moons of various sizes and part of Saturn's rings" src="https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=423&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=423&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=423&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506292/original/file-20230125-24-62k2ur.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Cassini spacecraft took this image showing part of Saturn’s rings, made of billions of small chunks of ice and rock, and five of its moons.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/jpl/group-portrait">NASA/JPL-Caltech/Space Science Institute</a></span>
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</figure>
<p>There are two funky exceptions: Uranus appears to have been tipped over on its side. Nobody knows exactly how. Maybe it collided with another planet. Venus is also odd – it spins backward. We don’t know for sure whether it formed that way or got knocked over. Most scientists now think its spin has been <a href="https://doi.org/10.1051/0004-6361/201628701">reversed over time</a> by <a href="https://doi.org/10.1038/275037a0">tidal forces</a> involving the Sun and Venus’ thick atmosphere.</p>
<p>All that leads <a href="https://www.uml.edu/sciences/physics/faculty/laycock-silas.aspx">astronomers like me</a> to wonder: Is there something about how the solar system formed that kind of “baked in” that direction of spin?</p>
<h2>Birth of a star</h2>
<p>For more clues, we can look at a young star, one that is just forming its system of planets.</p>
<p>A famous one is called <a href="https://www.cnn.com/2022/04/29/world/exocomet-discovery-beta-pictoris-scn/index.html">Beta Pictoris</a>. It is surrounded by a thin disk of dust, gas and little bits called planetesimals; they range in size from a grain of sand to rocks maybe up to the size of a mountain. Astronomers are pretty sure the disk formed from material left over when the star was born.</p>
<p>Every <a href="https://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve">star is born</a> from a cloud of gas and dust that moves through space surrounded by other similar clouds. The force of gravity causes these clouds to tug on one another as they pass, which makes them slowly rotate.</p>
<p>Even when one of these clouds <a href="https://spaceplace.nasa.gov/nebula/en/">collapses to form a star</a>, it continues to rotate. The star forms, spinning at the center of a flat pancake of rotating gas and dust called a <a href="https://public.nrao.edu/news/2018-alma-survey-disks/">protoplanetary disk</a>. All of it – the star, the gas, the dust – is spinning in the same direction.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Illustration of a star in the center of a slanted ring of debris shown as glowing against the star's light, with a planet in the foreground." src="https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506270/original/file-20230125-18-3xo4uj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist’s drawing shows what a planet orbiting Beta Pictoris might look like.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Artist%E2%80%99s_impression_of_the_planet_Beta_Pictoris_b.jpg">ESO L. Calçada/N. Risinger (skysurvey.org)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An image of the star from the Hubble Space Telescope show its main debris ring and what appears to be a second ring slightly off tilt." src="https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506267/original/file-20230125-24-102fb3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Hubble Space Telescope captured actual images of Beta Pictoris. Astronomers blocked out light from the star in the photo so the protoplanetary disk would be visible.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Beta_Pictoris#/media/File:HST_betaPictoris_comb.jpg">David Golimowski/Johns Hopkins University, NASA, ESA</a></span>
</figcaption>
</figure>
<p>Astronomers think that our solar system looked a lot like Beta Pictoris in its early years.</p>
<p>We think that inside the disk, the gas and dust can stick together in a <a href="https://astronomy.com/magazine/news/2022/06/the-physics-of-accretion">process called accretion</a>. As a baby planet starts to grow, it gets heavier, and its gravity attracts more and more little pieces.</p>
<p>When the baby planet gets massive enough, the force of gravity begins crushing it, <a href="https://exoplanets.nasa.gov/faq/43/how-do-planets-form/">making it denser</a>. Because of that, like an ice skater drawing in her arms to spin, the planet spins faster. Rising pressure in the core causes the core to melt. Denser materials sink toward the core, and lighter materials float to the planet’s surface. We end up with a planet with an iron core surrounded by rock, and maybe on the outer parts stuff like water and ice.</p>
<p>That’s <a href="https://education.nationalgeographic.org/resource/core">what we see in our solar system</a>.</p>
<h2>What if Earth didn’t spin?</h2>
<p>Earth’s spin is important for life. It causes day and night. It’s also <a href="https://moon.nasa.gov/resources/444/tides">important for ocean tides</a>. Without the daily ebb and flow of water, it’s <a href="https://www.scientificamerican.com/article/moon-life-tides/">possible life would never have emerged</a> from the sea onto land.</p>
<p>So, astronomers believe Earth spins because the entire solar system was already rotating when Earth formed – but there are still a lot of questions about how planets’ spins change over time, and how spin affects the evolution of life. With <a href="https://exoplanetarchive.ipac.caltech.edu">more than 5,000 planets now known beyond the solar system</a>, future scientists are going to be busy exploring.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>Editor’s note: This article was updated to remove the reference to Mercury.</em></p><img src="https://counter.theconversation.com/content/198402/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Silas Laycock receives funding from NSF and NASA. He is affiliated with UMass Lowell, and the American Astronomical Society. </span></em></p>An astronomer takes us on a tour of the universe to learn about the birth of stars and planets and how they get their spin.Silas Laycock, Professor of Astronomy, UMass LowellLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1980352023-02-09T16:59:27Z2023-02-09T16:59:27ZLight pollution has cut humanity’s ancient connection with the stars – but we can restore it<figure><img src="https://images.theconversation.com/files/508340/original/file-20230206-31-b29opi.jpg?ixlib=rb-1.1.0&rect=4%2C0%2C2991%2C1994&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/milky-way-rises-over-pine-trees-384983128">Andrey Prokhorov/Shutterstock</a></span></figcaption></figure><p>Humans are naturally afraid of the dark. We sometimes imagine monsters under the bed and walk faster down unlit streets at night. To conquer our fears, we may leave a night light on to scare away the monsters and a light over the porch to deter break-ins. </p>
<p>Yet, in huddling for safety under our pools of light, we have lost our connection to the night sky. Star counts by public awareness campaign <a href="https://www.globeatnight.org/">Globe at Night</a> revealed that, between 2011 and 2022, the world’s night sky <a href="https://www.theguardian.com/environment/2023/jan/19/light-pollution-rapidly-reducing-stars-visible-naked-eye-study-finds">more than doubled in artificial brightness</a>. Yet local interventions can create meaningful change. </p>
<p>Light pollution is cutting us off from one of nature’s greatest wonders, harming wildlife and blocking research that could help fight climate change. Stars are more than pretty glimmers in the night sky. They have shaped the mythology of every human civilisation. They guide birds on their astonishing migratory journeys. And now we need to do our bit to prevent light pollution so stars can be part of our future. </p>
<p><a href="https://skyandtelescope.org/astronomy-blogs/how-many-stars-night-sky-09172014/">The human eye can detect around 5,000</a> stars in the night sky. But the light emitted by skyscrapers, street lamps, and houses obscures all but a handful of the brightest stars. </p>
<p>Our ancestors used the rising and setting of the constellations as <a href="https://www.britannica.com/science/calendar/Time-determination-by-stars-Sun-and-Moon">calendars</a>. They also <a href="https://theconversation.com/how-far-theyll-go-moana-shows-the-power-of-polynesian-celestial-navigation-72375#:%7E:text=The%20position%20of%20Moana's%20hand,are%20travelling%20exactly%20due%20East.&text=Later%20in%20the%20film%2C%20we,by%20following%20Maui's%20fish%20hook.">navigated by the stars</a> as they searched for new lands or traced nautical trade routes. Sailors don’t normally use the stars to navigate any more, but they are still taught how to, <a href="https://www.popularmechanics.com/military/research/a36078957/celestial-navigation/">in case their navigation systems break down</a>. </p>
<p>Migratory animals, including birds and insects, are <a href="https://www.darksky.org/light-pollution/wildlife/">drawn away from their natural flight paths</a> by the beckoning “sky glow” of cities. In the summer of 2019, Las Vegas was <a href="https://www.smithsonianmag.com/smart-news/las-vegas-was-inundated-46-million-grasshoppers-single-night-2019-180977395/">invaded</a> by millions of migrating grasshoppers, while the beams of New York’s <a href="https://www.nytimes.com/2018/09/10/opinion/9-11-tribute-in-light-birds.html">9/11 Tribute in Light</a> are a magnet for flocks of migrating songbirds flying at night. </p>
<p>Disoriented by the bright city lights, birds crash into towering skyscrapers. Insect numbers are collapsing worldwide and light pollution is making matters worse by <a href="https://www.smithsonianmag.com/smart-news/light-pollution-contributes-insect-apocalypse-180973642/">disrupting their nocturnal life cycles</a>.</p>
<h2>What is light pollution</h2>
<p>Light pollution is caused by the same <a href="https://spaceplace.nasa.gov/blue-sky/en/">physics that turns the sky blue during the day</a>. Sunlight is made up of all the colours of the rainbow and each colour has a different wavelength. The air that surrounds us is composed of tiny particles (such as oxygen and carbon dioxide molecules). </p>
<p>As light from the Sun makes its way through the air, it is scattered by these particles in random directions. Blue light (with shorter wavelengths) is scattered more than red light (which has longer wavelengths). As a result, our eyes receive more blue light from every direction in the sky. </p>
<p>At night, light scattered by the same air particles causes the sky to shine down on us. A small fraction of this sky glow is caused by natural sources, such as starlight and the Earth’s atmosphere. But most of the light that creates sky glow is artificial. </p>
<figure class="align-center ">
<img alt="The constellation Orion, imaged at left from dark skies, and at right from the teeming metropolis of Orem, UT comprising about half a million people." src="https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=440&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=440&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=440&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=553&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=553&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=553&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Light pollution is not pretty.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Light_pollution_It%27s_not_pretty.jpg">Jeremy Stanley/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Light pollution also affects our ability to study the universe. Even modern observatories, built on remote mountaintops, are affected by the encroaching sky glow from growing, sprawling cities. Light pollution is so widespread that <a href="https://www.space.com/major-observatories-suffering-light-pollution">three quarters of all observatories</a> are affected. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/h0RKQmVAeQM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Migrating birds flying through Tribute in Light in 2015.</span></figcaption>
</figure>
<h2>Looking up</h2>
<p>There is no reason to despair, though. We created light pollution; we can fix it.</p>
<p>Around the world, <a href="https://www.darksky.org/">dark sky</a> <a href="https://www.darkskydiscovery.org.uk/">associations</a> are working to educate the public about the hazards of light pollution, to lobby for <a href="https://www.allaboutbirds.org/news/new-york-city-passes-landmark-lights-out-laws/">legislation to protect dark sky reserves</a> and encourage people to reignite their connection with <a href="https://www.darksky.org/our-work/lighting/">dark, star-studded skies</a>.</p>
<p><a href="https://theconversation.com/turn-off-the-porch-light-6-easy-ways-to-stop-light-pollution-from-harming-our-wildlife-132595">Fighting light pollution begins at home.</a> If you need to keep outside lights on for security, use shielded lamps that only shine downwards. Use light bulbs that do not emit violet and blue light as this is harmful to wildlife. Smart lighting controls will also help reduce your house’s effect on wildlife and make it easier for you to observe the night sky.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=267&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=267&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=267&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=336&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=336&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=336&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">2016 world map of artificial sky brightness. 80% of the world’s population is now affected by light pollution. Credit: Falchi et al., Science Advances, 2016;2:e160037.</span>
</figcaption>
</figure>
<p>You will also find <a href="https://www.lightpollutionmap.info">interactive maps</a> that show how polluted the skies are in your area. These maps are created from data gathered by satellites and by citizen scientists taking part in annual star counts. You can help darken our skies, too. </p>
<p>In the UK, the 2023 annual star count will take place on <a href="https://www.cpre.org.uk/what-we-care-about/nature-and-landscapes/dark-skies/star-count-2023/">February 17-24</a>. And, wherever you are in the world, you can always take part in the year-long <a href="https://globeatnight.org/">Globe at Night</a> star count whenever you want. </p>
<p>The task is simple: step outside on a clear night, count how many stars you can see in a well-known constellation, such as Orion, and report back. </p>
<p>To defeat light pollution, we need to know how severe it is and what difference national policies and local interventions (such as replacing the street lights in your town) make. In the UK, for example, star counts show light pollution may have <a href="https://www.cpre.org.uk/news/night-skies-outlook-is-bright-our-star-count-results-suggest/">peaked in 2020</a> and has started to decline. </p>
<p>Perhaps the most important aspect of star counts is that they shine a light on our vanishing night skies and galvanize us to take action. Ultimately, it’s up to each and every one of us to reduce our effect on the sky, by changing the way we light our homes and neighbourhoods and by lobbying our representatives to pass <a href="https://www.allaboutbirds.org/news/new-york-city-passes-landmark-lights-out-laws/#">dark sky legislation</a>. </p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p class="fine-print"><em><span>Or Graur does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>People travel hundreds or thousands of miles and spend a fortune to see the night sky in all its splendor. But we are literally blocking out the cosmic beauty above our homes.Or Graur, Reader in Astrophysics, University of PortsmouthLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1988672023-02-01T03:53:38Z2023-02-01T03:53:38ZAustralia is finally getting a last-chance view of a green comet not seen for 50,000 years<figure><img src="https://images.theconversation.com/files/507467/original/file-20230131-21-7p6s4z.jpg?ixlib=rb-1.1.0&rect=32%2C9%2C2993%2C2037&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/edu_inaf/52658472905/">Alessandro Bianconi/Edu INAF/Flickr </a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Over the past few weeks, social media has been abuzz with excited posts about the green comet that is currently “<a href="https://www.gulf-insider.com/dubai-witnesses-rare-comet-whizzing-across-sky/">whizzing</a>” or “flying through the sky”. </p>
<p>Now, comets don’t so much whizz as crawl. Despite that, there is a grain of truth in the reports – along with a whole heap of hype. </p>
<p>There is a relatively bright, green comet in the sky at the moment. Sadly, despite the hyperbole, you’re unlikely to spot it with the unaided eye – unless you have great eyesight, a dark sky, and know where to look.</p>
<p>People in the Northern Hemisphere have been following the comet for weeks. Now, for us in Australia, it will finally become visible, just a few days after its closest approach to Earth. So what’s all the fuss about?</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1616933701555740672"}"></div></p>
<h2>Green and rare</h2>
<p>Comet C/2022 E3 (ZTF) is a small dirty snowball discovered in March 2022 by the automated <a href="https://www.ztf.caltech.edu/">Zwicky Transient Facility</a> (hence the name ZTF).</p>
<p>Unlike asteroids, which are made of rock, comets are icy bodies. When they approach the Sun and the temperature rises, that icy surface sublimates (changes directly from a solid to a gas). The comet thus becomes shrouded in a fuzzy “coma” of gas and dust. Radiation pressure from the Sun, along with the effects of the <a href="https://www.britannica.com/science/solar-wind">solar wind</a>, pushes the gas and dust outwards, and the comet grows a “tail”. </p>
<p>The gas released by the comet is exposed to sunlight in the vacuum of space. That radiation, particularly the ultraviolet light, <a href="https://www.britannica.com/science/color/Physical-and-chemical-causes-of-colour#ref383867">excites the gas</a>. This means the gas gets rid of the energy it absorbs by shining in specific colours. </p>
<p>Much of the work astronomers do is based on breaking the light from distant objects into its component colours, to study what they are made of. Comet tails are usually blue, but comet ZTF has a very distinct greenish hue. Green is the telltale sign the comet is emitting large amounts of <a href="https://en.wikipedia.org/wiki/Diatomic_carbon">diatomic carbon</a> and <a href="https://en.wikipedia.org/wiki/Cyanogen">cyanogen</a>, which both create a greenish glow when excited.</p>
<p>So, by looking at the comet’s colour, we can immediately learn a bit about its composition – which is pretty cool!</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/507473/original/file-20230131-24-8j38ko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A dark star field with a bright green and white light on the lower-right corner, with two white streaks coming out of it in different directions" src="https://images.theconversation.com/files/507473/original/file-20230131-24-8j38ko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/507473/original/file-20230131-24-8j38ko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/507473/original/file-20230131-24-8j38ko.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/507473/original/file-20230131-24-8j38ko.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/507473/original/file-20230131-24-8j38ko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/507473/original/file-20230131-24-8j38ko.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/507473/original/file-20230131-24-8j38ko.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A close-up view of Comet C/2022 E3 (ZTF) on January 27 2023, captured at Lake Sonoma in California, US. You can see both its tail and even an ‘anti-tail’, an optical illusion caused by our viewing position on Earth.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/paranoidroid/52660668683/">Moshen Chan/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Upon discovery, the comet was just inside the orbit of Jupiter. Astronomers soon realised it would come relatively close to Earth in January and February this year, just a couple of weeks after its closest approach to the Sun (perihelion, <a href="https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2022E3&view=OPC">which came on January 12</a>).</p>
<p>Comet ZTF is a “long period comet”, which means it’s moving on an extremely elongated orbit around the Sun. It originated in the Oort cloud – a vast cloud of trillions of cometary nuclei that stretches halfway to the nearest star, leftovers from planetary formation 4.5 billion years ago. Those comets are held in cold storage until something nudges them inwards.</p>
<p>The last time comet ZTF graced the inner Solar System was around 50,000 years ago. While long period comets are not uncommon, interestingly this is likely ZTF’s final swing past our star. Thanks to a quirk of celestial mechanics, it is going to leave the Solar System altogether, travelling just fast enough to escape the Sun’s gravity.</p>
<p>Our Solar System (and all other planetary systems) are continually shedding comets like dandruff – with ZTF being just one more flake to add to the interstellar snowstorm.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1620388366196817920"}"></div></p>
<h2>A perfect ringside seat</h2>
<p>Now, under normal circumstances, comet ZTF would be solely of interest to keen amateur and professional astronomers. It is actually a relatively small comet, with a nucleus likely no more than a few hundred metres across.</p>
<p>Were it not for the fact of its relatively close approach, it would never get bright enough to be noteworthy.</p>
<p>Instead, pure chance has led to the comet passing through the inner Solar System at just the right time to come close to us. Instead of a dim and distant view, our planet has a perfect ringside seat to see the comet at its finest.</p>
<h2>When and where can we see it in Australia?</h2>
<p>At 17:54 UT on February 1 (that’s in the early morning of February 2 in Australia, around 5am on the east coast, but earlier in west), comet ZTF will be just under <a href="http://astro.vanbuitenen.nl/comet/2022E3">42.5 million kilometres</a> (0.284 au) from Earth. </p>
<p>Just as expected, the comet is now at its brightest – visible to observers in the Northern Hemisphere as a faint fuzzy blob (with the naked eye, from dark skies), albeit one that is made significantly harder to spot thanks to the glare of the nearly full Moon.</p>
<p>For observers in the Southern Hemisphere, we had to wait because the comet was too far in the northern sky – essentially “above” our planet in space.</p>
<p>Fortunately, the comet is now moving southwards at a rate of around <a href="https://in-the-sky.org/ephemeris.php?ird=1&irs=1&ima=1&iob=1&objtype=3&objpl=Mercury&objtxt=C%2F2022+E3+%28ZTF%29&tz=0&startday=1&startmonth=2&startyear=2023&interval=4&rows=25">five or six degrees per day</a> for the first ten days of February. Observers in the far north (Cairns and Darwin) might catch a glimpse low in the northern sky on the evening of February 2. Those in Hobart will have to wait until February 7 or 8 before it creeps high enough above the horizon to be spotted.</p>
<p>A good resource to check when the comet will be above the horizon from your home town is the free web-based planetarium package <a href="https://stellarium-web.org/">Stellarium</a>. Go to the site, pan around to the north, and set the clock (at the bottom right) to an hour or two after sunset – then step forward day by day until ‘C/2022 E3 (ZTF)’ is visible above the northern horizon.</p>
<h2>Get your gear ready</h2>
<p>Technically, the comet is currently bright enough to see with the naked eye. Eagle-eyed northern observers have been reporting sightings without optical aid since mid-January.</p>
<p>However, the comet is <em>only just</em> visible in this way – which means you need to know exactly where to look, and to have a really dark sky. And even if you can, what you see will likely be underwhelming – a dim fuzzy blob.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1620128140050972672"}"></div></p>
<p>By the time the comet is visible in Australia, it will be dimming quite rapidly, making it harder to see from one night to the next.</p>
<p>If you’re keen to see it, your best bet is to at least get a pair of binoculars. Work out where it should be, and scan the sky slowly, looking for a fuzzy patch of light.</p>
<p>The best time to find the comet will likely be February 11, when it will be within a degree of Mars, which currently shines bright and red, high to the north in the evening sky.</p>
<p>On the night of the 11th, find Mars with your binoculars, and pan just slightly to the right – you should be able to find the comet there.</p>
<p>But the best way to view the comet will be online. Astronomers worldwide are capturing incredible images of our celestial visitor. Taken with exposures many minutes in length, these photos reveal a view far better than anything possible with the naked eye.</p><img src="https://counter.theconversation.com/content/198867/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Skies in the Northern Hemisphere have been graced by a rare, green comet. Now, it’s our turn to look for it in Australia – but the view will be dimming rapidly.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.