tag:theconversation.com,2011:/ca/topics/cosmic-rays-2836/articlesCosmic rays – The Conversation2024-01-02T16:49:57Ztag:theconversation.com,2011:article/2195462024-01-02T16:49:57Z2024-01-02T16:49:57ZPrivatised Moon landings: the two US missions set to open a new era of commercial lunar exploration<figure><img src="https://images.theconversation.com/files/566549/original/file-20231219-23-qde9s6.jpeg?ixlib=rb-1.1.0&rect=0%2C2%2C1839%2C984&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/10836">Photograph: Nasa (Goddard Space Flight Center)</a></span></figcaption></figure><p>Two commercial spacecraft are scheduled to launch to the Moon early in 2024 under a Nasa initiative called the Commercial Lunar Payload Service <a href="https://www.nasa.gov/commercial-lunar-payload-services/">CLPS</a>. This programme is intended to kickstart a commercial transportation service that can deliver Nasa experiments and other payloads to the lunar surface.</p>
<p>If successful, these missions will represent the first landings on the Moon by spacecraft designed and flown by private companies. They could potentially open up a new era of commercial lunar exploration and science. </p>
<p>CLPS was inaugurated by Nasa in 2018. An initial pool of nine companies received an invitation to join the programme. They included <a href="https://www.astrobotic.com/">Astrobotic</a> and <a href="https://www.intuitivemachines.com/">Intuitive Machines</a>, the two companies behind these missions. Both missions expect to land within a week after lift-off.</p>
<p>The first launch, and the first Nasa flight of 2024, is the Peregrine lunar lander, built by Pittsburgh-based Astrobotic. It is scheduled to launch at the earliest on January 8. Broadly speaking, the lander is a box the size of a medium-sized garden shed containing several separate experiments. </p>
<p>These include a set of mirrors called a laser retro-reflector array, used for accurate positioning of the lander from orbit. There are also a number of spectrometers – instruments that separate and measure the distinct colours found in light. These will measure radiation on the lunar surface and look for signatures of water in lunar soil.</p>
<p>One of them, the <a href="https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=PEREGRN-1-02">Neutron Spectrometer System</a>, will look for hydrogen-containing materials on the surface, which can indicate the presence of water below ground. This water could one day be used by human explorers.</p>
<figure class="align-center ">
<img alt="Astrobotic Peregrine lander." src="https://images.theconversation.com/files/566548/original/file-20231219-19-i3ffem.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C1917%2C1279&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566548/original/file-20231219-19-i3ffem.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566548/original/file-20231219-19-i3ffem.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566548/original/file-20231219-19-i3ffem.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566548/original/file-20231219-19-i3ffem.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566548/original/file-20231219-19-i3ffem.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566548/original/file-20231219-19-i3ffem.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">
<figcaption>
<span class="caption">Astrobotic’s Peregrine lander will touch down near the Gruithuisen Domes.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details/KSC-20231114-PH-ILW01_0100">Isaac Watson/Nasa</a></span>
</figcaption>
</figure>
<p>There are two principle sources of dangerous radiation for humans in space. One is the Sun, which unleashes electrons, protons and heavier ions that are accelerated to a significant fraction of the speed of light. </p>
<p>These solar energetic particle events (SEPs) are more likely to occur during the Sun’s peak of activity (solar maximum), which occurs every 11 years. However, that does not mean there is a respite during the solar minimum.</p>
<p>The other source of harmful radiation is galactic cosmic rays (GCRs). These energetic particles originate outside the Solar System, probably in explosive phenomena such as exploding stars (supernovas).</p>
<p>During periods of lower solar activity (including the solar minimum), the Sun’s magnetic field, which extends throughout the Solar System, weakens. This enables <a href="https://www.researchgate.net/figure/Solar-cycle-%20modulation-and-anti-correlation-of-GCR-flux-with-solar-activity-Shown-are_fig6_257343697">more GCRs</a> to reach us instead. </p>
<p>Another spectrometer on Peregrine will measure both SEPs and GCRs on the Moon. This is important for examining how dangerous the radiation environment at the lunar surface will be for future human explorers.</p>
<h2>Polar landing</h2>
<p>The second spacecraft to launch early in 2024 is the <a href="https://www.intuitivemachines.com/im-1">Nova-C lander</a>. It is designed by Houston-based Intuitive Machines and has a similar volume to Peregrine, but in the shape of a tall, hexagonal cylinder. It will carry several instruments including its own laser retro-reflector array. Nova-C is currently scheduled to launch in mid-February.</p>
<p>Other instruments include a suite of cameras for producing a 3D image of Nova-C’s landing site. This will allow scientists to estimate how much material is blown away by the landing rocket’s exhaust plume during the descent. Potentially, any material blown away can be imaged to get an idea of the composition of surface material. </p>
<figure class="align-center ">
<img alt="Nova-C lander." src="https://images.theconversation.com/files/566583/original/file-20231219-23-2hpa5p.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566583/original/file-20231219-23-2hpa5p.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566583/original/file-20231219-23-2hpa5p.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566583/original/file-20231219-23-2hpa5p.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566583/original/file-20231219-23-2hpa5p.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566583/original/file-20231219-23-2hpa5p.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566583/original/file-20231219-23-2hpa5p.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">
<figcaption>
<span class="caption">A model of the Nova-C lander.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details/NHQ201905310022">Nasa (Goddard Space Flight Center)</a></span>
</figcaption>
</figure>
<p>The “radio observations of the lunar surface photo-electron sheath” (<a href="https://arxiv.org/pdf/2102.02331.pdf">Rolses</a>) instrument is designed to measure how the extremely tenuous lunar atmosphere and the Moon’s surface dust environment affect radio waves. </p>
<p>The behaviour of electrically charged dust particles on the Moon is a technical challenge which future explorers will need to deal with, as the abrasive particles can attach themselves to surfaces and mechanical devices and potentially cause harm if <a href="https://www.wired.com/story/the-%20next-big-challenge-for-lunar-astronauts-moon-dust/">inhaled</a> by astronauts.</p>
<p>A privately built experiment onboard Nova-C is the International Lunar Observatory <a href="https://iloa.org/ilo-x-precursor/">ILO-X</a>, which will aim to capture some of the first images of the Milky Way galaxy from the Moon’s surface. This would demonstrate the concept of lunar-based astronomy.</p>
<h2>Landing locations</h2>
<p>Peregrine’s landing site is a bay on the west side of Mare Imbrium, known as Sinus Viscositatis (Bay of Stickiness). Here, two volcanic mountains called the <a href="https://moon.nasa.gov/resources/482/a-lunar-%20mystery-the-gruithuisen-domes/">Gruithuisen Domes</a> are made of a different material to the surrounding plains. </p>
<p>The plains are a form of basalt, while the domes are composed of silica. Both are volcanic in origin, but one appears to have been formed by lava with a viscosity of mango chutney (the silica), and the other by runnier lava (the basalt). </p>
<figure class="align-center ">
<img alt="Gruithuisen Domes" src="https://images.theconversation.com/files/566614/original/file-20231219-29-7x7oaq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566614/original/file-20231219-29-7x7oaq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566614/original/file-20231219-29-7x7oaq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566614/original/file-20231219-29-7x7oaq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566614/original/file-20231219-29-7x7oaq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566614/original/file-20231219-29-7x7oaq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566614/original/file-20231219-29-7x7oaq.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">
<figcaption>
<span class="caption">The Gruithuisen Domes appear to have been formed by silica lavas.</span>
<span class="attribution"><a class="source" href="https://moon.nasa.gov/resources/482/a-lunar-mystery-the-gruithuisen-domes/">Nasa (GSFC)/Arizona State University</a></span>
</figcaption>
</figure>
<p>On Earth, silica lavas typically require the presence both of water and plate tectonics. However, plate tectonics are not known to be present on the Moon, and neither is water in the quantities necessary for silica lavas. The Gruithuisen Domes thus present a geological enigma which Peregrine could go some way to resolving.</p>
<p>The landing location for Nova-C is Malapert A crater – which is of particular interest for lunar exploration, as it lies close to the Moon’s south pole. The surrounding mountains permanently shield this depression from sunlight, leaving it in constant darkness. </p>
<p>Consequently, it is one of the coldest locations in the Solar System and, given the lack of sunlight, a place where water ice delivered by comets hitting the surface over the aeons could remain stable. Future human explorers could use it for life support and making rocket fuel.</p>
<figure class="align-center ">
<img alt="Lunar south pole." src="https://images.theconversation.com/files/566615/original/file-20231219-27-888tuc.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566615/original/file-20231219-27-888tuc.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566615/original/file-20231219-27-888tuc.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566615/original/file-20231219-27-888tuc.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566615/original/file-20231219-27-888tuc.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566615/original/file-20231219-27-888tuc.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566615/original/file-20231219-27-888tuc.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">An image of the Moon’s South Pole showing the Malapert crater (foreground).</span>
<span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/5127">Nasa's Scientific Visualization Studio</a></span>
</figcaption>
</figure>
<p>There are additional payloads on both spacecraft from private investors. Peregrine contains the “DHL Spacebox”, which will carry personal items from paying customers, while Nova-C contains “The Humanity Hall of Fame” – a list of names to be sent to the Moon for posterity. Such payloads can generate additional funding for the launch companies.</p>
<p>Several other companies are due to launch their first payloads to the Moon in the next couple of years. With greater input from private companies – assuming the these first few missions succeed – we may soon witness a new era in lunar exploration.</p><img src="https://counter.theconversation.com/content/219546/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Peregrine and Nova-C landers are due to carry out valuable science at two diverse lunar locations.Gareth Dorrian, Post Doctoral Research Fellow in Space Science, University of BirminghamIan Whittaker, Senior Lecturer in Physics, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2110752023-08-09T12:31:45Z2023-08-09T12:31:45ZResearchers dig deep underground in hopes of finally observing dark matter<figure><img src="https://images.theconversation.com/files/541255/original/file-20230804-21123-c0m9ny.jpeg?ixlib=rb-1.1.0&rect=11%2C0%2C1280%2C831&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The inside of the LZ outer detector. The LZ is a super sensitive machine that may one day detect a dark matter particle. </span> <span class="attribution"><span class="source">Matt Kapust, SURF</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Physicists like me don’t fully understand what makes up about <a href="https://doi.org/10.1051/0004-6361/201833910">83% of the matter of the universe</a> — something we call “<a href="https://theconversation.com/dark-matter-the-mystery-substance-physics-still-cant-identify-that-makes-up-the-majority-of-our-universe-85808">dark matter</a>.” But with a <a href="https://sanfordlab.org/experiment/lux-zeplin">tank full of xenon</a> buried nearly a mile under South Dakota, we might one day be able to measure what dark matter really is.</p>
<p>In the typical model, dark matter accounts for most of the gravitational attraction in the universe, providing the glue that allows structures like galaxies, including our own Milky Way, <a href="https://www.esa.int/Science_Exploration/Space_Science/Planck/History_of_cosmic_structure_formation">to form</a>. As the solar system orbits around the center of the Milky Way, Earth moves through a <a href="https://theconversation.com/dark-matter-our-method-for-catching-ghostly-haloes-could-help-unveil-what-its-made-of-147953">dark matter halo</a>, which makes up most of the matter in our galaxy. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541254/original/file-20230804-21-fug5qn.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the Milky Way galaxy, with a blurrred region or 'halo' around it indicating dark matter." src="https://images.theconversation.com/files/541254/original/file-20230804-21-fug5qn.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541254/original/file-20230804-21-fug5qn.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=601&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541254/original/file-20230804-21-fug5qn.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=601&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541254/original/file-20230804-21-fug5qn.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=601&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541254/original/file-20230804-21-fug5qn.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=755&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541254/original/file-20230804-21-fug5qn.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=755&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541254/original/file-20230804-21-fug5qn.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=755&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 rendition of the halo of dark matter surrounding the central spiral disk of the Milky Way.</span>
<span class="attribution"><span class="source">NASA/ESA/A Feild STSci</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>I’m a <a href="http://hep.ucsb.edu/people/hugh/">physicist</a> interested in understanding the nature of dark matter. One popular guess is that dark matter is a new type of particle, the <a href="https://www.britannica.com/science/weakly-interacting-massive-particle">Weakly Interacting Massive Particle</a>, or WIMP. “WIMP” captures the particle’s essence quite nicely – it has mass, meaning it interacts gravitationally, but it otherwise interacts very weakly – or rarely – with normal matter. WIMPs in the Milky Way theoretically fly through us on Earth all the time, but because they interact weakly, they just don’t hit anything.</p>
<h2>Searching for WIMPs</h2>
<p>Over the past 30 years, scientists have developed <a href="https://doi.org/10.48550/arXiv.2209.07426">an experimental program</a> to try to detect the rare interactions between WIMPs and regular atoms. On Earth, however, we are constantly surrounded by low, nondangerous levels of radioactivity coming from trace elements – mainly uranium and thorium – in the environment, as well as cosmic rays from space. The goal in hunting for dark matter is to build as sensitive a detector as possible, so it can see the dark matter, and to put it in as quiet a place as possible, so the dark matter signal can be seen over the background radioactivity. </p>
<p>With <a href="https://doi.org/10.1103/PhysRevLett.131.041002">results published in July 2023</a>, the <a href="https://sanfordlab.org/experiment/lux-zeplin">LUX-ZEPLIN</a>, or LZ, collaboration has done just that, building the largest dark matter detector to date and operating it 4,850 feet (1,478 meters) underground in the <a href="https://sanfordlab.org/">Sanford Underground Research Facility</a> in Lead, South Dakota. </p>
<p>At the center of LZ rests <a href="https://sanfordlab.org/feature/searching-dark-matter">10 metric tons (10,000 kilograms) of liquid xenon</a>. When particles pass through the detector, they may collide with xenon atoms, leading to a flash of light and the release of electrons.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541256/original/file-20230804-29-ohjyrk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a particle interacting and releasing an electron, which registers in the detector" src="https://images.theconversation.com/files/541256/original/file-20230804-29-ohjyrk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541256/original/file-20230804-29-ohjyrk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=627&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541256/original/file-20230804-29-ohjyrk.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=627&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541256/original/file-20230804-29-ohjyrk.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=627&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541256/original/file-20230804-29-ohjyrk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=788&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541256/original/file-20230804-29-ohjyrk.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=788&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541256/original/file-20230804-29-ohjyrk.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=788&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Particles interact with xenon in the LZ, releasing light that is detected by two light-sensing arrays at top and bottom.</span>
<span class="attribution"><span class="source">SLAC/LZ</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>In LZ, two massive electrical grids apply an electric field across the volume of liquid, which pushes these released electrons to the liquid’s surface. When they breach the surface, they are pulled into the space above the liquid, which is filled with xenon gas, and accelerated by another electric field to create a second flash of light. Two large arrays of light sensors collect these two flashes of light, and together they allow researchers to reconstruct the position, energy and type of interaction that took place. </p>
<h2>Reducing radioactivity</h2>
<p>All materials on Earth, including those used in WIMP detector construction, <a href="https://www.world-nuclear.org/information-library/safety-and-security/radiation-and-health/naturally-occurring-radioactive-materials-norm.aspx">emit some radiation</a> that could potentially mask dark matter interactions. Scientists therefore build dark matter detectors using the most “radiopure” materials – that is, free of radioactive contaminants – they can find, both inside and outside the detector. </p>
<p>For example, by working with metal foundries, LZ was able to use the <a href="https://doi.org/10.1016/j.astropartphys.2017.09.002">cleanest titanium on Earth</a> to build the central cylinder – or cryostat – that holds the liquid xenon. Using this special titanium reduces the radioactivity in LZ, creating a clear space to see any dark matter interactions. Furthermore, liquid xenon is so dense that it actually acts as a radiation shield, and it is easy to purify the xenon of radioactive contaminants that might sneak in. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541259/original/file-20230804-21-3lr4h7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An LZ worker wearing a white hazard suit stands by a tall white cylinder." src="https://images.theconversation.com/files/541259/original/file-20230804-21-3lr4h7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541259/original/file-20230804-21-3lr4h7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541259/original/file-20230804-21-3lr4h7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541259/original/file-20230804-21-3lr4h7.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541259/original/file-20230804-21-3lr4h7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541259/original/file-20230804-21-3lr4h7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541259/original/file-20230804-21-3lr4h7.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">In the inner detector of LZ, two light-sensing arrays at top and bottom view a central cylinder that will be filled with liquid xenon.</span>
<span class="attribution"><span class="source">Matt Kapust, SURF</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>In LZ, the central xenon detector lives inside two other detectors, called the xenon skin and the outer detector. These supporting layers catch radioactivity on the way in or out of the central xenon chamber. Because dark matter interactions are so rare, a dark matter particle will only ever interact one time in the entire apparatus. Thus, if we observe an event with multiple interactions in the xenon or the outer detector, we can assume it’s not being caused by a WIMP. </p>
<p>All of these objects, including the central detector, the cryostat and the outer detector, live in a large water tank nearly a mile underground. The water tank shields the detectors from the cavern, and the underground environment shields the water tank from cosmic rays, or charged particles that are constantly hitting the Earth’s atmosphere.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/dwoFeiqiNe0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The LZ lives underground to block out cosmic radiation. But in order to get it down there, SURF engineers had to figure out a way to transport all the machinery and equipment.</span></figcaption>
</figure>
<h2>The hunt continues</h2>
<p>In the result <a href="https://doi.org/10.1103/PhysRevLett.131.041002">just published</a>, using 60 days of data, LZ recorded about five events per day in the detector. That’s about a trillion fewer events than a typical particle detector on the surface would record in a day. By looking at the characteristics of these events, researchers can safely say that no interaction so far has been caused by dark matter. The result is, alas, not a discovery of new physics – but we can set limits on exactly how weakly dark matter must interact, as it remains unseen by LZ.</p>
<p>These limits help to tell physicists what dark matter is not – and LZ does that better than any experiment in the world. Meanwhile, there’s hope for what comes next in the search for dark matter. LZ is collecting more data now, and we expect to take more than 15 times more data over the next few years. A WIMP interaction may already be in that data set, just waiting to be revealed in the next round of analysis.</p><img src="https://counter.theconversation.com/content/211075/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hugh Lippincott receives funding from the US Department of Energy Office of Science. </span></em></p>To detect dark matter, you need to build an ultra-sensitive detector and put it somewhere ultra-quiet. For one physics collaboration, that place is almost a mile under Lead, S.D.Hugh Lippincott, Associate Professor of Physics, University of California, Santa BarbaraLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2086222023-06-29T20:01:42Z2023-06-29T20:01:42ZA neutrino portrait of our galaxy reveals high-energy particles from within the Milky Way<figure><img src="https://images.theconversation.com/files/534726/original/file-20230629-23-u6xkg.jpg?ixlib=rb-1.1.0&rect=643%2C0%2C1211%2C850&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">IceCube Collaboration/Science Communication Lab for CRC 1491</span></span></figcaption></figure><p>Our Milky Way galaxy is an awe-inspiring feature of the night sky, viewable with the naked eye as a hazy band of stars stretching from horizon to horizon.</p>
<p>For the first time, the IceCube Neutrino Observatory in Antarctica has produced an image of the Milky Way using neutrinos – tiny, ghost-like astronomical messengers. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534734/original/file-20230629-25-v10rmi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of the band of the Milky Way with extra shading in blue." src="https://images.theconversation.com/files/534734/original/file-20230629-25-v10rmi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534734/original/file-20230629-25-v10rmi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534734/original/file-20230629-25-v10rmi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534734/original/file-20230629-25-v10rmi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534734/original/file-20230629-25-v10rmi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534734/original/file-20230629-25-v10rmi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534734/original/file-20230629-25-v10rmi.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"></a>
<figcaption>
<span class="caption">A portrait of the Milky Way combining visible light and neutrino emissions (in blue).</span>
<span class="attribution"><span class="source">IceCube Collaboration/US National Science Foundation (Lily Le & Shawn Johnson)/ESO (S. Brunier)</span></span>
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<p>In <a href="http://dx.doi.org/10.1126/science.adc9818">research published today</a> in the journal Science, the IceCube Collaboration – an international group of more than 350 scientists – presents evidence of high-energy neutrino emission coming from the Milky Way.</p>
<p>We have not yet figured out exactly where in our galaxy these particles are coming from. But today’s result brings us closer to finding some of the galaxy’s most extreme environments.</p>
<h2>Neutrino astronomy</h2>
<p>Neutrinos offer a unique view of the cosmos as they can travel directly from places no other radiation or particles can escape from. This makes them very interesting to astronomers, because neutrinos offer a window into the extreme cosmic environments that create another kind of particle called cosmic rays.</p>
<p>Cosmic rays are high-energy particles that permeate our Universe, but their origins are difficult to pin down. Cosmic rays are electrically charged, which means their path through space is scrambled by magnetic fields, and by the time one arrives at Earth there is no way to tell where it came from. </p>
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<strong>
Read more:
<a href="https://theconversation.com/spotting-astrophysical-neutrinos-is-just-the-tip-of-the-icecube-20499">Spotting astrophysical neutrinos is just the tip of the IceCube</a>
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<p>However, the environments that accelerate cosmic rays to extraordinary energies also produce neutrinos – and neutrinos have no electric charge, so they travel in nice straight lines. So if we can detect the path of neutrinos arriving at Earth, this will point back to where the neutrinos were created. </p>
<p>But detecting those neutrinos is not so easy. </p>
<h2>How to hunt neutrinos</h2>
<p>The IceCube Neutrino Observatory is not far from the South Pole. It uses more than 5,000 light sensors arrayed throughout a cubic kilometre of pristine Antarctic ice to search for signs of high-energy neutrinos from our galaxy and beyond. </p>
<p>Vast numbers of neutrinos are streaming through Earth all the time, but only a tiny fraction of them bump into anything on their way through.</p>
<p>Each neutrino interaction makes a tiny flash of light – and those tiny flashes are what the IceCube sensors look out for. The direction and energy of the neutrino can be determined from the amount and pattern of light detected.</p>
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<a href="https://images.theconversation.com/files/534733/original/file-20230629-23-b8qav.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/534733/original/file-20230629-23-b8qav.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534733/original/file-20230629-23-b8qav.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534733/original/file-20230629-23-b8qav.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534733/original/file-20230629-23-b8qav.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534733/original/file-20230629-23-b8qav.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534733/original/file-20230629-23-b8qav.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534733/original/file-20230629-23-b8qav.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"></a>
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<span class="attribution"><span class="source">IceCube Collaboration</span></span>
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<p>IceCube has previously detected high-energy neutrinos coming from outside the Milky Way. However, it has been more challenging to isolate the lower-energy neutrinos coming from within our galaxy.</p>
<p>This is because some flashes IceCube detected can be traced to cosmic rays hitting Earth’s atmosphere, which create neutrinos and other particles called muons. To filter out these flashes, IceCube researchers have developed ways to distinguish particles created in the atmosphere and those from further afield by the shape of the light patterns they create in the ice. </p>
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<em>
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Read more:
<a href="https://theconversation.com/an-antarctic-neutrino-telescope-has-detected-a-signal-from-the-heart-of-a-nearby-active-galaxy-193845">An Antarctic neutrino telescope has detected a signal from the heart of a nearby active galaxy</a>
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<p>Filtering out the unwanted detections has made IceCube more sensitive to astrophysical neutrinos. The final breakthrough that allowed the creation of a neutrino image of the Milky Way came from machine-learning methods that improve the identification of cascades of light produced by neutrinos, as well as the determination of the neutrino’s direction and energy.</p>
<h2>Closing in on cosmic rays</h2>
<p>The new neutrino lens on our galaxy will help reveal where the most powerful accelerators of galactic cosmic rays are located. We hope to learn how energetic these particles can get, and the inner workings of these high-energy galactic engines.</p>
<p>However, we are yet to pinpoint these accelerators within the Milky Way. The new IceCube analysis found evidence for neutrinos coming from broad regions of the galaxy, but was not able to discern individual sources.</p>
<p>Our team, at the University of Canterbury in New Zealand and the University of Adelaide in Australia, has a plan to realise that next step.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534735/original/file-20230629-17-4f6jrd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/534735/original/file-20230629-17-4f6jrd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534735/original/file-20230629-17-4f6jrd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=342&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534735/original/file-20230629-17-4f6jrd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=342&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534735/original/file-20230629-17-4f6jrd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=342&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534735/original/file-20230629-17-4f6jrd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=430&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534735/original/file-20230629-17-4f6jrd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=430&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534735/original/file-20230629-17-4f6jrd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=430&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Five views of the Milky Way: the top two bands show visible light and gamma rays, while the lower three show expected and real neutrino results, plus a measure of the significance of neutrino events detected by IceCube.</span>
<span class="attribution"><span class="source">IceCube Collaboration</span></span>
</figcaption>
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<p>We are making models to predict the neutrino signal close to likely particle accelerators so we can target our searches for neutrinos. </p>
<p>Undergraduate student Rhia Hewett and PhD student Ryan Burley are examining pairs of accelerator candidates and molecular dust clouds. They plan to estimate the flux of neutrinos produced by cosmic rays interacting in the clouds, after the neutrinos travel from the accelerators. </p>
<p>They will use their results to enable a focused search of IceCube data for the sources of neutrino emissions. We believe this will provide the key to using IceCube to unlock the secrets of the most energetic processes in the Milky Way.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534731/original/file-20230629-22-fmkvpi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/534731/original/file-20230629-22-fmkvpi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534731/original/file-20230629-22-fmkvpi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=2067&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534731/original/file-20230629-22-fmkvpi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=2067&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534731/original/file-20230629-22-fmkvpi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=2067&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534731/original/file-20230629-22-fmkvpi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=2597&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534731/original/file-20230629-22-fmkvpi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=2597&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534731/original/file-20230629-22-fmkvpi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=2597&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">A timeline of neutrino astronomy.</span>
<span class="attribution"><span class="source">IceCube Collaboration</span></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/208622/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jenni Adams has received funding from the Marsden Fund Council from New Zealand Government funding, managed by the Royal Society Te Apārangi. </span></em></p>Neutrinos are some of nature’s most elusive particles, but new research has used them to create an image of our own galaxy.Jenni Adams, Professor, Physics and Astronomy, University of CanterburyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1930802022-10-25T23:04:46Z2022-10-25T23:04:46ZRadioactive traces in tree rings reveal Earth’s history of unexplained ‘radiation storms’<figure><img src="https://images.theconversation.com/files/491154/original/file-20221023-40716-6xlwd2.jpg?ixlib=rb-1.1.0&rect=52%2C37%2C4940%2C3952&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">University of Queensland</span></span></figcaption></figure><p>In searching for planets and studying their stars, I’ve had the privilege to use some of the world’s great telescopes. However, our team has recently turned to an even larger system to study the cosmos: Earth’s forests. </p>
<p>We analysed radioactive signatures left in tree rings around the world to study mysterious “radiation storms” that have swept over Earth half a dozen times in the past 10,000 years or so.</p>
<p>Our results, published today in <a href="https://doi.org/10.1098/rspa.2022.0497">Proceedings of the Royal Society A</a>, rule out “solar superflares” as the culprit – but the true cause remains unknown.</p>
<h2>A history written in tree rings</h2>
<p>When high-energy radiation strikes the upper atmosphere it turns nitrogen atoms into radioactive carbon-14, or radiocarbon. The radiocarbon then filters through the air and the oceans, into sediments and bogs, into you and me, into animals and plants - including hardwoods with their yearly tree rings. </p>
<p>To archaeologists, radiocarbon is a godsend. After it is created, carbon-14 slowly and steadily decays back into nitrogen – which means it can be used as a clock to measure the age of organic samples, in what is called <a href="https://www.nature.com/articles/s43586-021-00058-7">radiocarbon dating</a>. </p>
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Read more:
<a href="https://theconversation.com/explainer-what-is-radiocarbon-dating-and-how-does-it-work-9690">Explainer: what is radiocarbon dating and how does it work?</a>
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<p>To astronomers, this is equally valuable. Tree rings give a year-by-year record of high-energy particles called “cosmic rays” <a href="https://www.nature.com/articles/s41561-020-00674-0">going back millennia</a>. </p>
<p>The magnetic fields of Earth and the Sun shield us from cosmic rays shooting through the Galaxy. More cosmic rays reach Earth when these magnetic fields are weaker, and fewer when the fields are stronger.</p>
<p>This means the rise and fall of carbon-14 levels in tree rings encodes a history of <a href="https://sci-hub.se/10.1126/science.207.4426.11">the 11-year cycle of the solar dynamo</a> (which creates the Sun’s magnetic field) and the reversals of <a href="https://www.science.org/doi/full/10.1126/science.abb8677">Earth’s magnetic field</a>. </p>
<h2>Miyake events</h2>
<p>But tree rings also record events we cannot presently explain. In 2012, Japanese physicist Fusa Miyake <a href="https://ui.adsabs.harvard.edu/abs/2012Natur.486..240M/abstract">discovered a spike</a> in the radiocarbon content of tree rings from 774 AD. It was so big that several ordinary years’ worth of cosmic rays must have arrived all at once. </p>
<p>As more teams have joined the search, tree ring evidence has been uncovered of further “Miyake events”: from <a href="https://ui.adsabs.harvard.edu/abs/2013NatCo...4.1748M/abstract">993 AD</a> and <a href="https://www.cambridge.org/core/journals/radiocarbon/article/relationship-between-solar-activity-and-14c-peaks-in-ad-775-ad-994-and-660-bc/EFBDD78DEFAAA02B1CB9C3A24933B912">663 BC</a>, and prehistoric events in <a href="https://www.nature.com/articles/s41467-022-28804-9">5259 BC</a>, <a href="https://ui.adsabs.harvard.edu/abs/2021GeoRL..4893419M/abstract">5410 BC</a>, and <a href="https://www.nature.com/articles/s41467-021-27891-4">7176 BC</a>.</p>
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Read more:
<a href="https://theconversation.com/a-large-solar-storm-could-knock-out-the-power-grid-and-the-internet-an-electrical-engineer-explains-how-177982">A large solar storm could knock out the power grid and the internet – an electrical engineer explains how</a>
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<p>These have already led to a revolution in archaeology. Finding one of these short, sharp spikes in an ancient sample <a href="https://royalsocietypublishing.org/doi/10.1098/rspa.2016.0263">pins its date down to a single year</a>, instead of the decades or centuries of uncertainty from ordinary radiocarbon dating. </p>
<p>Among other things, our colleagues have used the 993 AD event <a href="https://www.nature.com/articles/s41586-021-03972-8">to reveal the exact year</a> of the first European settlement in the Americas, the Viking village at L'Anse aux Meadows in Newfoundland: 1021 AD. </p>
<h2>Could huge radiation pulses happen again?</h2>
<p>In physics and astronomy, these Miyake events remain a mystery. </p>
<p>How do you get such a huge pulse of radiation? A flurry of papers have blamed supernovae, <a href="https://ui.adsabs.harvard.edu/abs/2013MNRAS.430...32H">gamma-ray bursts</a>, <a href="https://ui.adsabs.harvard.edu/abs/2019ApJ...887..202W/abstract">explosions from magnetised neutron stars</a>, and even <a href="https://www.nature.com/articles/srep03728">comets</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/491521/original/file-20221025-18-a2bs48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photograph of solar flares emanating from the Sun." src="https://images.theconversation.com/files/491521/original/file-20221025-18-a2bs48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/491521/original/file-20221025-18-a2bs48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=491&fit=crop&dpr=1 600w, https://images.theconversation.com/files/491521/original/file-20221025-18-a2bs48.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=491&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/491521/original/file-20221025-18-a2bs48.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=491&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/491521/original/file-20221025-18-a2bs48.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=617&fit=crop&dpr=1 754w, https://images.theconversation.com/files/491521/original/file-20221025-18-a2bs48.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=617&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/491521/original/file-20221025-18-a2bs48.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=617&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Could ‘solar superflares’ be responsible for radiocarbon spikes in tree rings?</span>
<span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/images/pia21958-major-solar-flare">NASA / GSFC / Solar Dynamics Observatory</a></span>
</figcaption>
</figure>
<p>However, the <a href="https://ui.adsabs.harvard.edu/abs/2013A%26A...552L...3U/abstract">most widely accepted explanation</a> is that Miyake events are “solar superflares”. These hypothetical eruptions from the Sun would be perhaps 50–100 times more energetic than the biggest recorded in the modern era, the <a href="https://en.wikipedia.org/wiki/Carrington_Event">Carrington Event</a> of 1859. </p>
<p>If an event like this occurred today, it would <a href="https://astronomy.com/news/2021/09/understanding-just-how-big-solar-flares-can-get">devastate power grids, telecommunications, and satellites</a>. If these occur randomly, around once every thousand years, that is a 1% chance per decade – a serious risk. </p>
<h2>Noisy data</h2>
<p>Our team at UQ set out to sift through all the available tree ring data and pull out the intensity, timing, and duration of Miyake events. </p>
<p>To do this we had to develop software to solve a <a href="https://johncarlosbaez.wordpress.com/2012/07/24/carbon-cycle-box-models/">system of equations</a> that model how radiocarbon filters through the entire <a href="https://en.wikipedia.org/wiki/Carbon_cycle">global carbon cycle</a>, to work out what fraction ends up in trees in what years, as opposed to the oceans, bogs, or you and me. </p>
<p>Working with archaeologists, we have just released the first reproducible, systematic study of <a href="https://github.com/qingyuanzhang3/radiocarbon_workflow/tree/main/data">all 98 trees of published data</a> on Miyake events. We have also released <a href="https://sharmallama.github.io/ticktack">open source modelling software</a> as a platform for future work.</p>
<h2>Storms of solar flares</h2>
<p>Our results confirm each event delivers between one and four ordinary years’ worth of radiation in one go. <a href="https://www.nature.com/articles/s41467-018-05883-1">Earlier research</a> suggested trees closer to Earth’s poles recorded a bigger spike – which is what we would expect if solar superflares are responsible – but our work, looking at a larger sample of trees, shows this is not the case.</p>
<p>We also found these events can arrive at any point in the Sun’s 11-year activity cycle. Solar flares, on the other hand, <a href="https://link.springer.com/article/10.1007/s11207-021-01831-3">tend to happen</a> around <a href="https://arxiv.org/abs/2207.12787v2">the peak of the cycle</a>. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-is-the-sun-going-quiet-22155">Why is the sun going quiet?</a>
</strong>
</em>
</p>
<hr>
<p>Most puzzling, a couple of the spikes seem to take longer than can be explained by the slow creep of new radiocarbon through the carbon cycle. This suggests that either the events can sometimes take longer than a year, which is not expected for a giant solar flare, or the growing seasons of the trees are not as even as previously thought.</p>
<p>For my money, the Sun is still the most likely culprit for Miyake events. However, our results suggest we’re seeing something more like a storm of solar flares rather than one huge superflare. </p>
<p>To pin down what exactly happens in these events, we will need more data to give us a better picture of the events we already know about. To obtain this data, we will need more tree rings – and also other sources such as <a href="https://ui.adsabs.harvard.edu/abs/2015NatCo...6.8611M/abstract">ice cores from the Arctic and Antarctic</a>.</p>
<p>This is truly interdisciplinary science. Normally I think about beautifully clean, precise telescopes: it is much harder to understand the complex, interconnected Earth.</p><img src="https://counter.theconversation.com/content/193080/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjamin Pope receives funding from the Australian Research Council and the Big Questions Institute. </span></em></p>Half a dozen times in the past 10,000 years, enigmatic ‘Miyake events’ have showered Earth with cosmic rays.Benjamin Pope, ARC DECRA Fellow, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1779822022-03-18T12:31:42Z2022-03-18T12:31:42ZA large solar storm could knock out the power grid and the internet – an electrical engineer explains how<figure><img src="https://images.theconversation.com/files/452927/original/file-20220317-22992-n1ppek.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1500%2C997&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Typical amounts of solar particles hitting the earth's magnetosphere can be beautiful, but too much could be catastrophic.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Northern_Lights_-_Aurora_Borealis_Norway_Ringvass%C3%B8ya_Troms%C3%B8.jpg">Svein-Magne Tunli - tunliweb.no/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span></figcaption></figure><p>On Sept. 1 and 2, 1859, telegraph systems around the world failed catastrophically. The operators of the telegraphs reported receiving electrical shocks, telegraph paper catching fire, and being able to operate equipment <a href="https://arstechnica.com/science/2012/05/1859s-great-auroral-stormthe-week-the-sun-touched-the-earth/">with batteries disconnected</a>. During the evenings, the aurora borealis, more commonly known as the northern lights, could be seen as far south as Colombia. Typically, these lights are only visible at higher latitudes, in northern Canada, Scandinavia and Siberia.</p>
<p>What the world experienced that day, now known as the <a href="https://www.history.com/news/a-perfect-solar-superstorm-the-1859-carrington-event">Carrington Event</a>, was a massive <a href="https://theconversation.com/solar-storms-can-destroy-satellites-with-ease-a-space-weather-expert-explains-the-science-177510">geomagnetic storm</a>. These storms occur when a large bubble of superheated gas called plasma is ejected from the surface of the sun and hits the Earth. This bubble is known as a coronal mass ejection. </p>
<p>The plasma of a coronal mass ejection consists of a cloud of protons and electrons, which are electrically charged particles. When these particles reach the Earth, they interact with the magnetic field that surrounds the planet. This interaction causes the magnetic field to distort and weaken, which in turn leads to the strange behavior of the aurora borealis and other natural phenomena. As an <a href="https://www.researchgate.net/profile/David-Wallace-29">electrical engineer</a> who specializes in the power grid, I study how geomagnetic storms also threaten to cause power and internet outages and how to protect against that.</p>
<h2>Geomagnetic storms</h2>
<p>The Carrington Event of 1859 is the largest recorded account of a geomagnetic storm, but it is not an isolated event. </p>
<p>Geomagnetic storms have been recorded since the early 19th century, and scientific data from Antarctic ice core samples has shown evidence of an even more massive geomagnetic storm that <a href="https://doi.org/10.1038/nature11123">occurred around A.D. 774</a>, now known as the Miyake Event. That solar flare produced the largest and fastest rise in carbon-14 ever recorded. Geomagnetic storms trigger high amounts of cosmic rays in Earth’s upper atmosphere, which in turn produce <a href="https://www.radiation-dosimetry.org/what-is-carbon-14-production-properties-decay-definition/">carbon-14</a>, a radioactive isotope of carbon.</p>
<p>A geomagnetic storm 60% smaller than the Miyake Event <a href="https://doi.org/10.1038/ncomms2783">occurred around A.D. 993</a>. Ice core samples have shown evidence that large-scale geomagnetic storms with similar intensities as the Miyake and Carrington events occur at an average rate of once every 500 years.</p>
<p>Nowadays the National Oceanic and Atmospheric Administration uses the <a href="https://www.swpc.noaa.gov/noaa-scales-explanation">Geomagnetic Storms scale</a> to measure the strength of these solar eruptions. The “G scale” has a rating from 1 to 5 with G1 being minor and G5 being extreme. The Carrington Event would have been rated G5. </p>
<p>It gets even scarier when you compare the Carrington Event with the Miyake Event. Scientist were able to estimate the strength of the Carrington Event <a href="https://doi.org/10.1007/s11207-005-4980-z">based on the fluctuations of Earth’s magnetic field</a> as recorded by observatories at the time. There was no way to measure the magnetic fluctuation of the Miyake event. Instead, scientists measured the increase in carbon-14 in tree rings from that time period. The Miyake Event produced a <a href="https://doi.org/10.1038/nature11123">12% increase in carbon-14</a>. By comparison, the Carrington Event produced less than 1% increase in Carbon-14, so the Miyake Event likely dwarfed the G5 Carrington Event.</p>
<h2>Knocking out power</h2>
<p>Today, a geomagnetic storm of the same intensity as the Carrington Event would affect far more than telegraph wires and could be catastrophic. With the ever-growing dependency on electricity and emerging technology, any disruption could lead to trillions of dollars of monetary loss and risk to life dependent on the systems. The storm would affect <a href="https://www.cnet.com/science/we-arent-ready-for-a-solar-storm-smackdown/">a majority of the electrical systems</a> that people use every day.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/JncTCE2NWgc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The National Weather Service operates the Space Weather Prediction Center, which watches for solar flares that could lead to geomagnetic storms.</span></figcaption>
</figure>
<p>Geomagnetic storms generate induced currents, which flow through the electrical grid. The geomagnetically <a href="https://www.electricalclassroom.com/what-is-induced-current/">induced currents</a>, which can be in excess of 100 amperes, flow into the electrical components connected to the grid, such as transformers, relays and sensors. One hundred amperes is equivalent to the electrical service provided to many households. Currents this size can cause internal damage in the components, leading to large scale power outages.</p>
<p>A geomagnetic storm three times smaller than the Carrington Event occurred in Quebec, Canada, in March 1989. The storm <a href="https://www.nasa.gov/topics/earth/features/sun_darkness.html">caused the Hydro-Quebec electrical grid to collapse</a>. During the storm, the high magnetically induced currents damaged a transformer in New Jersey and tripped the grid’s circuit breakers. In this case, the outage led to <a href="https://doi.org/10.1038/484311a">five million people being without power for nine hours</a>.</p>
<h2>Breaking connections</h2>
<p>In addition to electrical failures, communications would be disrupted on a worldwide scale. Internet service providers could go down, which in turn would take out the ability of different systems to communicate with each other. High-frequency communication systems such as ground-to-air, shortwave and ship-to-shore radio would be disrupted. Satellites in orbit around the Earth could be damaged by induced currents from the geomagnetic storm burning out their circuit boards. This would lead to <a href="https://www.cnet.com/science/we-arent-ready-for-a-solar-storm-smackdown/">disruptions</a> in satellite-based telephone, internet, radio and television.</p>
<p>[<em>Get fascinating science, health and technology news.</em> <a href="https://memberservices.theconversation.com/newsletters/?nl=science&source=inline-science-fascinating">Sign up for The Conversation’s weekly science newsletter</a>.]</p>
<p>Also, as geomagnetic storms hit the Earth, the increase in solar activity causes the atmosphere to expand outward. This expansion changes the density of the atmosphere where satellites are orbiting. Higher density atmosphere <a href="https://theconversation.com/solar-storms-can-destroy-satellites-with-ease-a-space-weather-expert-explains-the-science-177510">creates drag</a> on a satellite, which slows it down. And if it isn’t maneuvered to a higher orbit, it can fall back to Earth.</p>
<p>One other area of disruption that would potentially affect everyday life is navigation systems. Virtually every mode of transportation, from cars to airplanes, use GPS for navigation and tracking. Even handheld devices such as cell phones, smart watches and tracking tags rely on GPS signals sent from satellites. Military systems are heavily dependent on GPS for coordination. Other military detection systems such as over-the-horizon radar and submarine detection systems could be disrupted, which would hamper national defense.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/452924/original/file-20220317-22992-qysj2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A crew works on a machine with a giant spool laying a cable in the water" src="https://images.theconversation.com/files/452924/original/file-20220317-22992-qysj2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/452924/original/file-20220317-22992-qysj2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=369&fit=crop&dpr=1 600w, https://images.theconversation.com/files/452924/original/file-20220317-22992-qysj2x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=369&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/452924/original/file-20220317-22992-qysj2x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=369&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/452924/original/file-20220317-22992-qysj2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=464&fit=crop&dpr=1 754w, https://images.theconversation.com/files/452924/original/file-20220317-22992-qysj2x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=464&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/452924/original/file-20220317-22992-qysj2x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=464&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 global internet is held together by a network of cables crisscrossing the world’s oceans.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/germany-mecklenburg-western-pomerania-baltic-sea-undersea-news-photo/548151689">Jens Köhler/ullstein bild via Getty Images</a></span>
</figcaption>
</figure>
<p>In terms of the internet, a geomagnetic storm on the scale of the Carrington Event could <a href="https://dl.acm.org/doi/10.1145/3452296.3472916">produce geomagnetically induced currents in the submarine and terrestrial cables</a> that form the backbone of the internet as well as the data centers that store and process everything from email and text messages to scientific data sets and artificial intelligence tools. This would potentially disrupt the entire network and prevent the servers from connecting to each other.</p>
<h2>Just a matter of time</h2>
<p>It is only a matter of time before the Earth is hit by another geomagnetic storm. A Carrington Event-size storm would be <a href="https://www.swpc.noaa.gov/sites/default/files/images/u33/finalBoulderPresentation042611%20%281%29.pdf">extremely damaging</a> to the electrical and communication systems worldwide with outages lasting into the weeks. If the storm is the size of the Miyake Event, the results would be catastrophic for the world with potential outages lasting months if not longer. Even with <a href="https://www.weather.gov/safety/space-ww">space weather warnings</a> from NOAA’s Space Weather Prediction Center, the world would have only a few minutes to a few hours notice.</p>
<p>I believe it is critical to continue researching ways to protect electrical systems against the effects of geomagnetic storms, for example by <a href="https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-21033.pdf">installing devices that can shield vulnerable equipment</a> like transformers and by developing strategies for adjusting grid loads when solar storms are about to hit. In short, it’s important to work now to minimize the disruptions from the next Carrington Event.</p><img src="https://counter.theconversation.com/content/177982/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Wallace 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>Every few centuries the sun blasts the Earth with a huge amount of high-energy particles. If it were to happen today, it would wreak havoc on technology.David Wallace, Assistant Clinical Professor of Electrical Engineering, Mississippi State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1001552018-08-28T21:06:19Z2018-08-28T21:06:19ZNew era of astronomy uncovers clues about the cosmos<figure><img src="https://images.theconversation.com/files/231953/original/file-20180814-2894-1tzyen8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An illustration of two neutron stars spinning around each other while merging.</span> <span class="attribution"><span class="source"> NASA/CXC/Trinity University/D. Pooley et al.</span></span></figcaption></figure><p>Astronomers have had a blockbuster year. </p>
<p>In addition to tracking down <a href="https://theconversation.com/the-icecube-observatory-detects-neutrino-and-discovers-a-blazar-as-its-source-99720">a cosmic source of neutrinos</a>, they have detected the merger of <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">two city-sized neutron stars, each more massive than the sun</a>. </p>
<p>The <a href="https://www.ligo.org/science/Publication-GW170817MMA/">discoveries were heralded</a> as evidence that a “<a href="https://www.ligo.org/science/Publication-GW170817MMA/">new era of multimessenger astronomy</a>” had arrived. </p>
<p>But what is multimessenger astronomy? </p>
<p>In our daily lives, we interpret the world around us based on different signals, such as sound waves, light (a type of electromagnetic wave) and skin pressure. Each of these signals may be carried by a different “messenger.” New messengers lead to new insights. So astronomers have eagerly welcomed a new set of messengers to their science.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=432&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=432&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=432&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=543&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=543&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=543&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Twenty-seven radio antennas make up the Karl G. Very Large Array in New Mexico. The VLA is an important tool for studying cosmic radio waves.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Many messengers</h2>
<p>For most of the history of astronomy, scientists primarily studied signals transmitted by one messenger, electromagnetic radiation. These waves, which move through space and time, are described by their wavelengths or the amount of energy found in their particles, the photons.</p>
<p>Radio waves have photons with the lowest amount of energy and the longest wavelengths, followed by infrared and optical light at intermediate energies and wavelengths. X-rays and gamma-rays have the shortest wavelengths and the highest energy. </p>
<p>But scientists study others messengers too: </p>
<ul>
<li>Cosmic rays: charged atomic particles and nuclei travelling near the speed of light.</li>
<li>Neutrinos: uncharged particles that see most of the universe as transparent.</li>
<li>Gravitational waves: wrinkles in the very fabric of space and time.</li>
</ul>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?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">The four messengers of astronomy.</span>
<span class="attribution"><span class="source">Adapted from IceCube Collaboration</span></span>
</figcaption>
</figure>
<p>And while some fields in astronomy have explored these messengers for years, astronomers have only recently observed events from well beyond the Milky Way with more than one messenger at the same time. In just a few months, the number of sources where astronomers can piece together the signals from different messengers doubled.</p>
<h2>Like a walk on the beach</h2>
<p>Multimessenger astronomy is a natural evolution of astronomy. Scientists need more data to put together a complete picture of the objects they study and match the theories they develop with their observations. </p>
<p>Astronomers have combined different wavelengths of photons to piece together some of the mysteries of the universe. For example, the combination of radio and optical data played a major role in determining that the Milky Way is a spiral galaxy in 1951.</p>
<p>And astronomy continues to reveal great results about our universe using just one messenger, photons. So if multimessenger astronomy is just an evolutionary step of an incredible history of successes, does that mean it’s just a new buzzword?</p>
<p>We don’t think so.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=398&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=398&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=398&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An artistic rendition of NASA’s Chandra X-ray Observatory. This space satellite produces the most detailed X-ray images of high energy astrophysical phenomena.</span>
<span class="attribution"><span class="source">NGST</span></span>
</figcaption>
</figure>
<p>Imagine you are walking along an ocean beach. You are enjoying the sight of an incredible sunset, hearing the rolling waves, feeling the sand beneath your feet and smelling the salty air. Your combined senses form a more complete experience. </p>
<p>With multimessenger astronomy, we hope to learn more from the universe by combining multiple messengers, just as we combine sight, hearing, touch and smell.</p>
<h2>But it’s not always a picnic</h2>
<p>The cultures of astronomers and particle physicists represent different approaches to science. In multimessenger astronomy, these cultures collide.</p>
<p>Astronomy is an observational field and not an experiment. We study astronomical objects that change over time (time-domain astronomy), which means we often have only one chance to observe a transient astronomical event.</p>
<p>Until recently, most time-domain astronomers worked in small teams, on many projects at once. We use resources like <a href="http://www.astronomerstelegram.org/">The Astronomer’s Telegram</a> or the <a href="https://gcn.gsfc.nasa.gov/">Gamma-ray Coordination Network</a> to rapidly communicate results, even before submitting scientific papers.</p>
<p>Since most of the expected sources of multimessenger signals are transient astronomical events, it’s a huge effort to capture the messengers besides photons.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/the-icecube-observatory-detects-neutrino-and-discovers-a-blazar-as-its-source-99720">The IceCube observatory detects neutrino and discovers a blazar as its source</a>
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<p>Particle physicists have led the way in creating large international collaborations to tackle their hardest problems, including the <a href="https://home.cern/topics/large-hadron-collider">Large Hadron Collider</a>, the <a href="https://icecube.wisc.edu/">IceCube Neutrino Observatory</a> and the <a href="https://www.ligo.caltech.edu/">Laser Interferometer Gravitational-Wave Observatory (LIGO)</a>. Corralling hundreds to thousands of researchers to work towards common goals requires comprehensive identification of roles, strict communication guidelines and many teleconferences.</p>
<p>The need to respond to rapid changes in a multimessenger source and the huge effort to capture multimessenger signals means astronomy and particle physics must merge towards one another to elicit the best of both cultures.</p>
<h2>The benefits of multimessenger astronomy</h2>
<p>While multimessenger astronomy is an evolution of what astronomers and particle physicists have done for decades, the combined results are intriguing.</p>
<p>The detection of gravitational waves from merging neutron stars confirmed that <a href="https://theconversation.com/cosmic-alchemy-colliding-neutron-stars-show-us-how-the-universe-creates-gold-86104">these collisions made a large fraction of the gold and platinum</a> on Earth (and throughout the universe). It also showed how these collisions give rise to (at least some) <a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">short gamma-ray bursts</a> — the origin of these explosive events has been a huge open question in astronomy. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.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">
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<span class="caption">The IceCube Neutrino Observatory used a cubic kilometre of crystal-clear Antarctic ice to capture the signal of a rare neutrino that helped pinpoint a galaxy four billion light years away with a supermassive black hole launching a jet of photons and near light-speed particles directly at our Solar System.</span>
<span class="attribution"><span class="source">IceCube Collaboration/NSF</span></span>
</figcaption>
</figure>
<p>The first association of a neutrino with a single astronomical source provided a glimpse into how the universe makes its most energetic particles. Multimessenger astronomy is revealing details about some of the most extreme conditions in our universe.</p>
<p>The multimessenger perspective is already yielding more than the sum of its parts — and we can expect to see more surprising discoveries in the future. Elite teams across Canada are already contributing to the growth of this young field, and multimessenger astronomy promises to play a major role in our next decade of astronomical research in Canada — and across the world.</p><img src="https://counter.theconversation.com/content/100155/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gregory Sivakoff receives funding from Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Foundation for Innovation (CFI), and Alberta Economic Development and Trade (EDT). Gregory Sivakoff is a member of several professional societies for astronomy and physics, including the Canadian Astronomical Society (CASCA), Canadian Association of Physicists (CAP), American Astronomical Society (AAS), and the AAS High Energy Astrophysics Division (HEAD). Gregory Sivakoff also serves on the Council of the American Association of Variable Star Observers (AAVSO), a non-profit citizen astronomy organization.
</span></em></p><p class="fine-print"><em><span>Daryl Haggard receives funding from the Canadian Institute for Advanced Research (CIFAR) Azrieli Global Scholars Program, Natural Sciences and Engineering Research Council of Canada (NSERC), the Fonds de Recherche du Québec – Nature et technologies (FRQNT). Daryl Haggard is a member of several professional societies for astronomy and physics, including the Canadian Astronomical Society (CASCA), Canadian Association of Physicists (CAP), American Astronomical Society (AAS), and the AAS High Energy Astrophysics Division (HEAD). Daryl Haggard also serves on the Laser Interferometer Gravitational-Wave Observatory (LIGO) Program Advisory Committee.</span></em></p>Astronomers are now able to detect a host of signals streaming through the universe. This newfound ability is like gaining new senses and it’s opening the door to understanding the cosmos.Gregory Sivakoff, Associate Professor, University of AlbertaDaryl Haggard, Assistant Professor of Physics, McGill UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/843802017-09-21T19:43:17Z2017-09-21T19:43:17ZThe origin of extreme cosmic ray particles revealed: they come from distant galaxies<figure><img src="https://images.theconversation.com/files/186923/original/file-20170921-19169-ms4sn2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Detecting cosmic ray particles: a water-Cherenkov detector seen against the night sky at the Pierre Auger Observatory in western Argentina.</span> <span class="attribution"><span class="source">Steven Saffi, University of Adelaide</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The existence of high-energy cosmic ray particles bombarding Earth was first discovered in the 1960s, but their origin was a mystery. </p>
<p>Now a paper published today in the journal <a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aao5651">Science</a> reports that the extremely energetic cosmic ray particles originate from outside our own Milky Way.</p>
<p>For the first time, scientists have conclusive evidence that real matter, nuclei of various chemical elements, is speeding to Earth from other galaxies.</p>
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<strong>
Read more:
<a href="https://theconversation.com/3d-view-helps-us-to-understand-how-galaxies-formed-and-evolved-81318">3D view helps us to understand how galaxies formed and evolved</a>
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<p>Cosmic rays are actually protons and nuclei that barrel through space at speeds almost equal to that of light. <a href="https://www.space.com/32644-cosmic-rays.html">First discovered in 1912</a>, the true range of their energies was only realised in the 1960s when some cosmic rays were discovered to have very high energies, as much as a fast-bowled cricket ball packed into an atomic nucleus. </p>
<p>Lower-energy cosmic rays are known to be produced in our Milky Way in powerful events such as supernova explosions.</p>
<p>But it was not known if the rare, highest-energy particles were created in our own galaxy or in distant ones. These particles have energies at least a million times larger than the protons accelerated at the Large Hadron Collider in Europe.</p>
<h2>A big observatory</h2>
<p>The new discovery was made with the help of the <a href="http://www.auger.org/">Pierre Auger Observatory</a> that covers 3,000 square kilometres at the base of the Andes in western Argentina. It has mapped the arrival directions of more than 30,000 of the most energetic cosmic rays. </p>
<p>We found that the arrival rate of cosmic rays is 6% greater from one side of the sky than from the opposite direction, with the excess lying well away from the plane of the Milky Way and its centre. </p>
<p>It seems that our galaxy does not contain the sort of extreme environments capable of producing the highes-energy particles.</p>
<p>The Auger observatory is almost as large as Kangaroo Island (off the South Australia coast), and needs to be huge because these cosmic rays arrive at a rate of only one per square kilometre per year.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/_ZNqTVk1_Tk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Cosmic rays heading for Earth.</span></figcaption>
</figure>
<p>The observatory takes advantage of huge cascades of subatomic particles initiated by an energetic cosmic ray colliding with the Earth’s atmosphere. A single cascade, or “air shower”, contains upwards of 10 billion particles in a disk-like swarm several kilometres wide.</p>
<p>At ground level the cascade can be seen by an array of 1,600 particle detectors distributed over the observatory. At night, a series of large telescopes view the faint blue light emitted by the cascade in our atmosphere. </p>
<p>Both techniques accurately measure the arrival direction and the energy of the original cosmic ray particle.</p>
<p>This large observatory is operated by a huge international team - 400 scientists from 18 countries, including a group of 16 physicists from the University of Adelaide. (Adelaide actually hosted the first planning workshop for the observatory 25 years ago.) </p>
<p>It began taking data in 2004, with the University of Adelaide taking the lead in several areas, by finding the best ways of measuring the cosmic ray energies and directions, and co-leading studies of the nature (mass and charge) of the cosmic rays.</p>
<h2>The search for sources</h2>
<p>Conventional wisdom during the planning for the Auger observatory was that the highest-energy cosmic rays would be protons, nuclei of hydrogen atoms.</p>
<p>Instead, one of the experiment’s <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.90.122006">major discoveries a few years ago</a> was that the particles are a mixture of protons and heavier nuclei. Since nuclei are charged particles, and since magnetic fields fill the universe, the paths of cosmic rays are bent during their propagation to Earth. This complicates the search for cosmic ray sources. </p>
<p>Given these facts, the result published today is all the more remarkable. The pattern of the 30,000 arrival directions on the sky is uneven, and significantly so. </p>
<p>Such an uneven sky map could arise by chance from an underlying uniform distribution, but only with a likelihood of 1 in 5 million. The excess is well away from the directions of the Milky Way plane and centre, and in a direction where the density of other galaxies is relatively high. </p>
<p>Although this discovery demonstrates an origin outside the Milky Way, the actual sources have yet to be pinned down. The direction of the excess points to a broad area of sky rather than to specific galaxies, as even particles as energetic as these are typically deflected by a few tens of degrees in the magnetic field of our galaxy.</p>
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<strong>
Read more:
<a href="https://theconversation.com/expect-the-unexpected-from-the-big-data-boom-in-radio-astronomy-84059">Expect the unexpected from the big-data boom in radio astronomy</a>
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<p>The source galaxies must be more extreme than our own. Candidates include galaxies with active central supermassive black holes, or pairs of galaxies in collision.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/186934/original/file-20170921-16430-7o0nga.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/186934/original/file-20170921-16430-7o0nga.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/186934/original/file-20170921-16430-7o0nga.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/186934/original/file-20170921-16430-7o0nga.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/186934/original/file-20170921-16430-7o0nga.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/186934/original/file-20170921-16430-7o0nga.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/186934/original/file-20170921-16430-7o0nga.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/186934/original/file-20170921-16430-7o0nga.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&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 Auger Observatory water-Cherenkov detector on the Pampa Amarilla in western Argentina.</span>
<span class="attribution"><span class="source">The Pierre Auger Observatory</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The Auger observatory is undergoing a major upgrade to be completed in 2018. Currently it can only identify the cosmic ray mass with its optical telescopes (which operate 15% of the time).</p>
<p>The upgrade will arm the surface array with the ability to measure mass 24 hours per day. The plan is to use this new capability to select extremely energetic <em>proton</em> cosmic rays, those with expected magnetic deflections of less than a few degrees. </p>
<p>Then we will have a real chance of identifying which galaxies, or class of galaxy, are responsible for producing the most energetic particles known in the universe.</p><img src="https://counter.theconversation.com/content/84380/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bruce Dawson receives funding from the Australian Research Council and the Australian government's National Collaborative Research Infrastructure Strategy (NCRIS).</span></em></p>Scientists say they now know that high energy cosmic ray particles that bombard Earth are coming from outside our galaxy. But the actual source still remains a mystery.Bruce Dawson, Professor, University of AdelaideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/787902017-06-08T02:37:10Z2017-06-08T02:37:10ZAir travel exposes you to radiation – how much health risk comes with it?<figure><img src="https://images.theconversation.com/files/172470/original/file-20170606-3698-c0rfrt.jpg?ixlib=rb-1.1.0&rect=86%2C0%2C5216%2C3371&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Captain, we're being pummeled by cosmic rays!</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/passenger-airplane-clouds-travel-by-air-568662646">muratart via Shutterstock.com</a></span></figcaption></figure><p>In 2017, <a href="http://www.independent.ie/business/world/18-million-miles-and-counting-the-globes-top-business-traveller-35666790.html">business traveler Tom Stuker</a> was hailed as the world’s most frequent flyer, logging 18,000,000 miles of air travel on United Airlines over 14 years. </p>
<p>That’s a lot of time up in the air. If Stuker’s traveling behaviors are typical of other business flyers, he may have eaten 6,500 <a href="http://www.airliners.net/forum/viewtopic.php?t=689041">inflight meals</a>, drunk 5,250 <a href="https://doi.org/10.1111/j.1708-8305.2009.00339.x">alcoholic beverages</a>, watched thousands of <a href="http://www.iata.org/publications/store/Pages/global-passenger-survey.aspx">inflight movies</a> and made around 10,000 visits to <a href="http://blog.thetravelinsider.info/2012/11/how-many-restrooms-are-enough-on-a-plane.html">airplane toilets</a>.</p>
<p>He would also have accumulated a radiation dose equivalent to about 1,000 <a href="https://www.radiologyinfo.org/en/info.cfm?pg=safety-xray">chest x-rays</a>. But what kind of health risk does all that radiation actually pose?</p>
<h2>Cosmic rays coming at you</h2>
<p>You might guess that a frequent flyer’s radiation dose is coming from the airport security checkpoints, with their whole-body scanners and baggage x-ray machines, but you’d be wrong. The <a href="http://www.aapm.org/publicgeneral/AirportScannersPressRelease.asp">radiation doses to passengers from these security procedures</a> are trivial. </p>
<p>The major source of radiation exposure from air travel comes from the flight itself. This is because at high altitude the <a href="http://www.altitude.org/why_less_oxygen.php">air gets thinner</a>. The farther you go from the Earth’s surface, the fewer molecules of gas there are per volume of space. Thinner air thus means fewer molecules to deflect incoming <a href="http://www.space.com/32644-cosmic-rays.html">cosmic rays</a> – radiation from outer space. With less <a href="http://www.bbc.co.uk/science/earth/atmosphere_and_climate/atmosphere">atmospheric shielding</a>, there is more exposure to radiation. </p>
<p>The most extreme situation is for astronauts who travel entirely outside of the Earth’s atmosphere and enjoy none of its protective shielding. Consequently, they receive high radiation doses. In fact, it is the accumulation of radiation dose that is the limiting factor for the maximum length of manned space flights. Too long in space and <a href="https://www.nasa.gov/hrp/bodyinspace">astronauts risk cataracts, cancer and potential heart ailments</a> when they get back home.</p>
<p>Indeed, it’s the radiation dose problem that is a major spoiler for <a href="http://www.space.com/34210-elon-musk-unveils-spacex-mars-colony-ship.html">Elon Musk’s goal of inhabiting Mars</a>. An extended stay on Mars, with its <a href="http://www.space.com/16903-mars-atmosphere-climate-weather.html">extremely thin atmosphere</a>, would be lethal due to the high radiation doses, notwithstanding Matt Damon’s successful Mars colonization in the movie <a href="https://www.youtube.com/watch?v=ej3ioOneTy8">“The Martian</a>.”</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/172329/original/file-20170605-16895-1rv1y9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/172329/original/file-20170605-16895-1rv1y9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/172329/original/file-20170605-16895-1rv1y9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/172329/original/file-20170605-16895-1rv1y9u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/172329/original/file-20170605-16895-1rv1y9u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/172329/original/file-20170605-16895-1rv1y9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/172329/original/file-20170605-16895-1rv1y9u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/172329/original/file-20170605-16895-1rv1y9u.jpg?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>
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<span class="caption">Air travel means exposure to some radiation… but how much are we talking about?</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/johnjones/5575498919">John Jones</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<h2>Radiation risks of ultra frequent flying</h2>
<p>What would be Stuker’s cumulative radiation dose and what are his health risks?</p>
<p>It depends entirely on how much time he has spent in the air. Assuming an <a href="http://hypertextbook.com/facts/2002/JobyJosekutty.shtml">average flight speed</a> (550 mph), Stuker’s 18,000,000 miles would translate into 32,727 hours (3.7 years) of flight time. The radiation dose rate at typical <a href="http://www.telegraph.co.uk/travel/travel-truths/why-do-planes-fly-so-high-feet/">commercial airline flight altitude</a> (35,000 feet) is about <a href="https://hps.org/publicinformation/ate/faqs/commercialflights.html">0.003 millisieverts per hour</a>. (As I explain in my book <a href="http://press.princeton.edu/titles/10691.html">“Strange Glow: The Story of Radiation</a>,” a millisievert or mSv is a unit of radiation dose that can be used to estimate cancer risk.) By multiplying the dose rate by the hours of flight time, we can see that Stuker has earned himself about 100 mSv of radiation dose, in addition to a lot of free airline tickets. But what does that mean for his health?</p>
<p>The primary health threat at this dose level is an increased risk of some type of cancer later in life. Studies of atomic bomb victims, nuclear workers and medical radiation patients have <a href="https://doi.org/10.17226/11340">allowed scientists to estimate the cancer risk</a> for any particular radiation dose. </p>
<p>All else being equal and assuming that low doses have risk levels proportionate to high doses, then an overall cancer risk rate of <a href="http://www.imagewisely.org/imaging-modalities/computed-tomography/medical-physicists/articles/how-to-understand-and-communicate-radiation-risk">0.005 percent per mSv</a> is a reasonable and commonly used estimate. Thus, Stuker’s 100-mSv dose would increase his lifetime risk of contracting a potentially fatal cancer by about 0.5 percent.</p>
<h2>Contextualizing the risk</h2>
<p>The question then becomes whether that’s a high level of risk. Your own feeling might depend on how you see your background cancer risk.</p>
<p>Most people <a href="http://www.who.int/whr/2002/chapter3/en/index4.html">underestimate their personal risk of dying from cancer</a>. Although the exact number is debatable, it’s fair to say that <a href="https://www.cancer.org/cancer/cancer-basics/lifetime-probability-of-developing-or-dying-from-cancer.html">about 25 percent of men ultimately contract a potentially fatal cancer</a>. Stuker’s 0.5 percent cancer risk from radiation should be added to his baseline risk – so it would go from 25 percent to 25.5 percent. A cancer risk increase of that size is too small to actually measure in any scientific way, so it must remain a theoretical increase in risk.</p>
<p>A 0.5 percent increase in risk is the same as one chance in 200 of getting cancer. In other words, if 200 male travelers logged 18,000,000 miles of air travel, like Stuker did, we might expect just one of them to contract a cancer thanks to his flight time. The other 199 travelers would suffer no health effects. So the chances that Stuker is the specific 18-million-mile traveler who would be so unlucky is quite small.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/172295/original/file-20170605-16869-17w9epo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/172295/original/file-20170605-16869-17w9epo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/172295/original/file-20170605-16869-17w9epo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1044&fit=crop&dpr=1 600w, https://images.theconversation.com/files/172295/original/file-20170605-16869-17w9epo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1044&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/172295/original/file-20170605-16869-17w9epo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1044&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/172295/original/file-20170605-16869-17w9epo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1313&fit=crop&dpr=1 754w, https://images.theconversation.com/files/172295/original/file-20170605-16869-17w9epo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1313&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/172295/original/file-20170605-16869-17w9epo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1313&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Airline personnel are typically the most frequent of fliers.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/bogers/150447878">Bas Bogers</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Stuker was logging more air hours per year (greater than 2,000) than most pilots typically log (<a href="http://work.chron.com/duty-limitations-faa-pilot-17646.html">under 1,000</a>). So these airline workers would have risk levels proportionately lower than Stuker’s. But what about you? </p>
<p>If you want to know your personal cancer risk from flying, estimate all of your commercial airline miles over the years. Assuming that the values and parameters for speed, radiation dose and risk stated above for Stuker are also true for you, dividing your total miles by 3,700,000,000 will give your approximate odds of getting cancer from your flying time.</p>
<p>For example, let’s pretend that you have a mathematically convenient 370,000 total flying miles. That would mean 370,000 miles divided by 3,700,000,000, which comes out to be 1/10,000 odds of contracting cancer (or a 0.01 percent increase in risk). Most people do not fly 370,000 miles (equal to 150 flights from Los Angeles to New York) within their lifetimes. So for the average flyer, the increased risk is far less than 0.01 percent.</p>
<p>To make your exercise complete, make a list of all the benefits that you’ve derived from your air travel over your lifetime (job opportunities, vacation travel, family visits and so on) and go back and look at your increased cancer risk again. If you think your benefits have been meager compared to your elevated cancer risk, maybe its time to rethink flying. But for many people today, flying is a necessity of life, and the small elevated cancer risk is worth the price.</p><img src="https://counter.theconversation.com/content/78790/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Timothy J. Jorgensen 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>The true radiation risk from commercial flying has nothing to do with security scans. A radiation expert explains how much cancer risk the most frequent of flyers take on when they take to the skies.Timothy J. Jorgensen, Director of the Health Physics and Radiation Protection Graduate Program and Professor of Radiation Medicine, Georgetown UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/465212016-01-10T19:15:06Z2016-01-10T19:15:06ZShooting the moon: the search for ultra high energy neutrinos<figure><img src="https://images.theconversation.com/files/100589/original/image-20151103-16519-1bboosy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The moon can be used to help in the hunt for high energy particles.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/byneilhall/9994710003/">Flickr/Neil Hall </a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>In 1991 physicists first detected a cosmic ray – a high-energy particle from space – with an energy beyond anything they’d dreamed of. They called it the <a href="https://www.quantamagazine.org/20150514-the-particle-that-broke-a-cosmic-speed-limit/">Oh-My-God particle</a>.</p>
<p>Probably the nucleus of an iron atom, it carried about 3x10<sup>20</sup> electron volts (eV), the energy of a well-bowled cricket ball, but this was contained in a single particle. This is also way beyond the energy that the Large Hadron Collider (LHC) can give a particle, which is about 10<sup>15</sup>eV.</p>
<p>More of these ultra-high-energy particles have been seen in the past 25 years but they are very rare, arriving at a rate of one per square kilometre per century. It’s hard to reach such high energies within our galaxy so the particles probably come from beyond it. </p>
<h2>From a place far, far away</h2>
<p>Being charged, cosmic-ray particles are deflected as they travel through our galaxy’s magnetic fields, making it difficult to tell where they come from. But we might learn that by studying one of their by-products, neutrinos, which were the focus of <a href="https://theconversation.com/how-neutrinos-which-barely-exist-just-ran-off-with-another-nobel-prize-48726">this year’s Nobel Prize for Physics</a>.</p>
<p>Cosmic rays with energies beyond 5x10<sup>19</sup>eV should interact with the photons of the cosmic microwave background, producing high-energy neutrinos. Being uncharged, neutrinos travel in straight lines, and their direction of arrival points back towards their origin. </p>
<p>Neutrinos are interesting in their own right, too, and can be used to test some of the more exotic theories of particle formation in the early universe.</p>
<p>Neutrinos interact very little with other matter. That means they can bring us astronomical information from the most distant reaches of the universe. But it also means that to find them you need a really large detector. </p>
<h2>The moon’s a detector</h2>
<p>Fortunately, we can use our moon. In 1962 a Russian-Armenian physicist, Gurgen Askaryan, predicted that neutrinos interacting with rocks under the moon’s surface would generate a flash of radio waves lasting just a nanosecond – known as the Askaryan effect – and that this could be detected by a receiver on the moon.</p>
<p>In 1992 two Russians, R Dagkesamanskii and I M Zheleznykh, suggested that you wouldn’t need to put a receiver on the moon, you could just point a ground-based radio telescope at it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/100586/original/image-20151103-16554-13sjghx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/100586/original/image-20151103-16554-13sjghx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/100586/original/image-20151103-16554-13sjghx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/100586/original/image-20151103-16554-13sjghx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/100586/original/image-20151103-16554-13sjghx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/100586/original/image-20151103-16554-13sjghx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/100586/original/image-20151103-16554-13sjghx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/100586/original/image-20151103-16554-13sjghx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&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 Askaryan effect: an ultra-high-energy neutrino interacts with the sub-surface rocks of the moon, generating a shower of radio photons that can be detected by a radio telescope on Earth.</span>
<span class="attribution"><span class="source">Ron Ekers</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>When I heard Zheleznykh talk about this in the early 1990s I realised that we could do the experiment – the first of its kind – with CSIRO’s <a href="http://www.parkes.atnf.csiro.au/">Parkes telescope</a> in New South Wales. I put it together in 1995 with Tim Hankins, a US colleague, and John O'Sullivan, who had
led CSIRO’s development of Wi-Fi.</p>
<p>That first experiment gave us a limit rather than any detection, but it also triggered a new interest in using radio observations to study high-energy particles.</p>
<p>Two US researchers ran a second such experiment in the early 2000s, using NASA’s 70-metre antenna at <a href="http://www.gdscc.nasa.gov/">Goldstone</a> in California. This gained a lot of attention but we knew we could do a better one, at least ten times more sensitive. This time we used CSIRO’s <a href="https://www.narrabri.atnf.csiro.au/">Compact Array</a>, a set of six 22-metre dishes in northwest NSW. </p>
<p>The array had a big advantage over Goldstone: it let us distinguish between radio pulses coming from the moon and those from terrestrial signals (radio-frequency interference). But some effort was needed to adapt it for detecting extremely short pulses. </p>
<p>So for our third experiment we decided to try again with Parkes, and use a different way to handle the radio-frequency interference.</p>
<p>Parkes has a radio receiver that lets it see 13 spots on the sky simultaneously. This, plus some technical wizardry from CSIRO engineer Paul Roberts, let us eliminate all the radio-frequency interference: a huge achievement. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/100587/original/image-20151103-16542-491o3k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/100587/original/image-20151103-16542-491o3k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/100587/original/image-20151103-16542-491o3k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=458&fit=crop&dpr=1 600w, https://images.theconversation.com/files/100587/original/image-20151103-16542-491o3k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=458&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/100587/original/image-20151103-16542-491o3k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=458&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/100587/original/image-20151103-16542-491o3k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=576&fit=crop&dpr=1 754w, https://images.theconversation.com/files/100587/original/image-20151103-16542-491o3k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=576&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/100587/original/image-20151103-16542-491o3k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=576&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 CSIRO Parkes telescope’s 13-beam receiver being lifted into the telescope’s focus cabin. Each of the instrument’s 13 holes ‘sees’ a separate spot on the sky.</span>
<span class="attribution"><span class="source">CSIRO</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We also used the timing signals from the GPS satellites, to measure the density of free electrons in the ionosphere, the upper part of the atmosphere, and even a piezoelectric barbecue lighter which made a radio impulse we used to calibrate signals.</p>
<p>In the past 15 years other research groups had entered the fray, but this second Parkes experiment was three times more sensitive than any previous one of its kind, and we pushed the limit on the flux of ultra-high-energy cosmic neutrinos down to its lowest level.</p>
<p>There’s a lot of wiggle room in the theories of how high-energy neutrinos are produced, but as observations tighten the limits the theorists have to gradually rule out some of their original ideas.</p>
<h2>Future observations</h2>
<p>The <a href="https://icecube.wisc.edu/">IceCube</a> experiment in Antarctica <a href="http://phys.org/news/2013-11-world-largest-particle-detector-icecube.html">recently detected</a> the first high-energy neutrinos from space, but these are still 10,000 times less energetic than the extremely rare ones we have been looking for.</p>
<p>There are other experiments proposed or in train that might find these elusive particles, including a satellite that uses the whole of the atmosphere as its detector.</p>
<p>The coming Square Kilometre Array (<a href="https://theconversation.com/au/topics/square-kilometre-array">SKA</a>) is the obvious instrument to try again to detect the neutrinos and there are discussions about how it could be used in an experiment.</p>
<p>With just a little bit more sensitivity than we had, which you could easily get with the SKA, the hope is that one day we could detect not only neutrinos but also the original cosmic rays interacting with the moon.</p><img src="https://counter.theconversation.com/content/46521/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ron Ekers receives funding from the ARC and CSIRO. </span></em></p>When looking for evidence of some of the universe’s mysterious high energy particles, why not enlist the help of our nearest neighbour: the moon.Ron Ekers, CSIRO Fellow, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/499792015-11-13T10:52:30Z2015-11-13T10:52:30ZScientist at work: searching for tiny neutrinos in the South Pole’s thick ice<figure><img src="https://images.theconversation.com/files/101719/original/image-20151112-9362-1al7h43.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ice cold physics: hunting for neutrinos in Antarctica.</span> <span class="attribution"><a class="source" href="http://icecube.wisc.edu/gallery/press/view/1336">Sven Lidström, IceCube/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Standing at the South Pole is the next-best thing to being on another planet. If you walk a few hundred yards away from the buildings that make up the National Science Foundation’s <a href="https://www.nsf.gov/news/special_reports/livingsouthpole/intro.jsp">research station</a>, you see a featureless plain of snow and ice, most likely empty of living creatures larger than microbes for hundreds of miles. With nothing but snow for sound waves to echo off, there’s an eerie silence. It’s easy to get lost in reverie, contemplating the stark landscape. But then you remember that you’re here for a reason: to work on what may be the world’s weirdest telescope, searching for some of nature’s most mysterious subatomic particles.</p>
<p>Every second, more than <a href="http://pdg.lbl.gov/2015/reviews/rpp2014-rev-cosmic-rays.pdf">10,000 high-energy particles</a> – protons and atomic nuclei – rain down on every square meter of the Earth’s atmosphere. Some of them carry more than a million times the energy of the protons at the most powerful particle accelerator, CERN’s <a href="http://home.cern/topics/large-hadron-collider">Large Hadron Collider</a>. Fortunately, the atmosphere absorbs most of them, but a few stray particles pass through your body every second – they’re the reason intercontinental airline crews are classified as <a href="http://www.cdc.gov/niosh/topics/aircrew/cosmicionizingradiation.html">radiation workers</a>.</p>
<p>Scientists discovered these particles, known as cosmic rays, more than a century ago, before <a href="https://theconversation.com/from-newton-to-einstein-the-origins-of-general-relativity-50013">Einstein’s theory of general relativity</a> or <a href="http://www.nbi.ku.dk/english/www/niels/bohr/bohratomet/">Bohr’s quantum mechanical model</a> of the atom. But even today, despite half a dozen Nobel Prizes awarded for research related to cosmic rays, we’re not sure where these particles come from. The magnetic fields that fill the universe deflect cosmic rays on their way to Earth, so the direction they’re traveling when they reach us doesn’t tell us where they were originally produced. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/101731/original/image-20151112-9381-3cnoxx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Constructing the support tower for the hot water ‘drill’ used to melt holes 1.5 miles deep in the Antarctic ice to install IceCube sensors.</span>
<span class="attribution"><a class="source" href="http://icecube.wisc.edu/gallery/view/170">Jeff Cherwinka, IceCube/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Neutrinos hint at where cosmic rays come from</h2>
<p>I’m part of an international team of scientists who built an unusual type of telescope to look for the sources of the cosmic rays. Since the cosmic rays themselves don’t point back to their sources, we look instead for neutrinos, a type of subatomic particle that should be produced as a byproduct of cosmic ray acceleration, wherever it’s happening. (The same process occurs when cosmic rays hit our atmosphere; these “atmospheric” neutrinos were used to discover neutrino oscillations by one of the two experiments that won <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2015/">2015’s Nobel Prize in Physics</a>.)</p>
<p><a href="https://theconversation.com/how-neutrinos-which-barely-exist-just-ran-off-with-another-nobel-prize-48726">Neutrinos are very strange</a> – they’ve been called ghost particles. They very rarely interact with other matter, so to see them, you need a very large detector. Our telescope is called <a href="http://icecube.wisc.edu">IceCube</a>, because we use a cubic kilometer – a billion tons – of the Antarctic ice cap to catch neutrinos.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/101746/original/image-20151112-9366-17htjfm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&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 IceCube’s 86 strings of sensors, called DOMs (digital optical modules), being lowered into the ice. They’re vertically spaced about 17 meters apart and meant to catch the visual repercussions of a neutrino collision.</span>
<span class="attribution"><a class="source" href="http://icecube.wisc.edu/gallery/press/view/1336">Jim Haugen, IceCube/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Most neutrinos pass invisibly through IceCube, but by chance a few of them will smash into a proton or neutron in the ice, releasing a shower of relativistic particles we <em>can</em> see. By measuring the number and direction of these visible particles, we can determine the direction the original neutrino came from, its energy, and its type or “flavor.” One by one, we build up a picture of the sky as it shines in neutrinos, rather than starlight.</p>
<p>Antarctica may not sound like the obvious place to build such a telescope, but in fact it’s the easiest and cheapest place to do it. The US maintains a <a href="https://www.nsf.gov/geo/plr/support/southp.jsp">scientific facility at the South Pole</a>, home to several other experiments besides IceCube. Most importantly for us, the South Pole station sits on top of nearly three kilometers of the purest, clearest ice in the world – a perfect neutrino target just waiting to be used.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/101729/original/image-20151112-9385-s93ygo.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"></a>
<figcaption>
<span class="caption">Planes need skis to land and take off at the South Pole.</span>
<span class="attribution"><a class="source" href="http://icecube.wisc.edu/gallery/view/211">Mark Krasberg, IceCube/NSF</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Good for science, tough for people</h2>
<p>But “easiest” is not the same as “easy” – the South Pole is a challenging place to work. Traveling to the pole from the US can take a week or more. The last leg of the trip is on a special ski-equipped C-130 cargo aircraft operated by the Air National Guard, which lands on a runway made of compressed snow. These aircraft can only reach the pole for four months of the year: at midsummer (January, in the southern hemisphere), the average temperature is a balmy -15 degrees Fahrenheit (-26 degrees Celsius), but by March temperatures have fallen to -50F (-45C), too cold for C-130s to operate. We pack our work into those summer months, then hand IceCube off to two hardy “winter-over” scientists. Our winter-overs are part of a team of 45 people who stay at the station for the rest of the year, cut off from the rest of the world for eight months except for internet and radio communications. </p>
<p>In the summer, the station population expands to about 150. The South Pole is a high-altitude desert, so the air is thin and very, very dry. But the cold isn’t the toughest part of working at the South Pole – at least in the summer. The strangest thing, at least for me, is the constant daylight. At the South Pole, the sun stays up for six months, circling along the horizon and slowly spiraling down until it sets at the autumn equinox. Then our winter-overs get six months of constant darkness until sunrise in the spring. This plays havoc with circadian rhythms; I’ve awoken to see the clock read 3:00, not knowing whether it’s am or pm, whether I’ve slept for four hours or 16.</p>
<p>Despite being one of the most isolated places on Earth, the station is also very crowded in the summer. It takes a lot of expensive fuel to heat buildings, so space is at a premium, and needless to say most of us work indoors. It also takes fuel to melt water, so showers are rationed to two minutes of running water twice a week, contributing to the unique working atmosphere at the South Pole. </p>
<h2>Results starting to roll in</h2>
<p>After seven years of work, IceCube was fully commissioned in 2011, on schedule and on budget. Coordinating the efforts of around 250 scientists around the world was another challenge, and that was only the beginning. Most new telescopes are validated by observing known sources: stars, pulsars, radio galaxies. But there are no known high-energy neutrino sources – IceCube is opening an entirely new window on the universe – so we had to convince ourselves and the rest of the scientific community that we know what we are seeing.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/3PZgfPHULHw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A neutrino interacting with the ice inside the IceCube telescope produces electrically charged secondary particles that are detected thanks to a process called Cherenkov radiation. The Cherenkov light, a blue light emitted by charged particles passing through a medium at a speed greater than the speed of light in that medium, will spread through the ice over hundreds of meters.</span></figcaption>
</figure>
<p>Two years after IceCube was completed, we <a href="http://inspirehep.net/record/1265461">announced</a> that we had identified our first two neutrinos from outside the solar system – the first entries in our map of the neutrino sky. (We named them Bert and Ernie.) Last year we recorded the <a href="http://www.astronomerstelegram.org/?read=7856">highest-energy neutrino ever seen</a>: 1,000 times the energy of the protons accelerated at CERN.</p>
<p>There’s a wonderful debate in the scientific community over where these neutrinos come from, whether any of them might be produced in our own galaxy or even be related to exotic new particles like dark matter. As we take more data, we hope more exciting new discoveries are in store.</p><img src="https://counter.theconversation.com/content/49979/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tyce DeYoung receives funding from the US National Science Foundation. </span></em></p>A cubic kilometer of clear, stable ice could help physicists answer big questions about cosmic rays and neutrinos. Hardy scientists collect data via a unique telescope at the frozen bottom of the world.Tyce DeYoung, Associate Professor of Physics and Astronomy, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/466362015-08-28T13:30:17Z2015-08-28T13:30:17ZSix amazing sights that look even better from the International Space Station<figure><img src="https://images.theconversation.com/files/92927/original/image-20150825-15875-1pkpm9z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hurricane Arthur photographed by ESA astronaut Alexander Gerst.</span> <span class="attribution"><span class="source">ESA/NASA</span></span></figcaption></figure><p>Imagine seeing the lights of cities spreading around <a href="http://www.nasa.gov/multimedia/imagegallery/image_feature_1923.html">the Nile Delta</a> and then in less than an hour gazing down on <a href="http://www.nasa.gov/multimedia/imagegallery/image_feature_152.html">Mount Everest</a>. The astronauts on the <a href="http://www.nasa.gov/mission_pages/station/main/index.html">International Space Station</a> (ISS) are among the lucky few who will have this humbling, once-in-a-lifetime experience of seeing the beauty of Earth from space. </p>
<p>The ISS doesn’t just offer spectacular and countless views of the natural and man-made landscapes of our planet. It also immerses its residents into the Earth’s space environment and reveals how dynamic its atmosphere is, from its lower layers to its protective <a href="http://www.swpc.noaa.gov/phenomena/earths-magnetosphere">magnetic shield</a>, constantly swept by the solar wind.</p>
<p>The best views are seen from <a href="http://www.esa.int/Our_Activities/Human_Spaceflight/Views_from_Cupola">the Cupola</a>, an observation deck module attached to the ISS in 2010 and comprising seven windows. So, what are the amazing sights that you can see from the space station?</p>
<h2>1. Storms and lightning</h2>
<p>When the ISS orbits over a sea of thunderclouds, it’s not rare for astronauts to witness an impressive amount of lightning. What is unusual, however, is seeing lightning sprites, which were <a href="http://earthobservatory.nasa.gov/IOTD/view.php?id=86463">observed on August 10th</a> by astronauts aboard the space station.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/92911/original/image-20150825-17055-o3talf.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/92911/original/image-20150825-17055-o3talf.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/92911/original/image-20150825-17055-o3talf.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/92911/original/image-20150825-17055-o3talf.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/92911/original/image-20150825-17055-o3talf.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/92911/original/image-20150825-17055-o3talf.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/92911/original/image-20150825-17055-o3talf.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">
<figcaption>
<span class="caption">ISS astronauts spotted a sprite (the red jellyfish-like structure on the right of the image) appearing above thunder clouds on August 10, 2015.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Sprites are electrical discharges, similar to thunder lights. However, instead of occurring in the lower layer of Earth’s atmosphere, these very fast, red-coloured discharges (due to the excited nitrogen at this altitude) occur much higher up and are as such difficult to observe from the ground.</p>
<h2>2. Sunrises and sunsets</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/92928/original/image-20150825-15896-1ar0fkw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/92928/original/image-20150825-15896-1ar0fkw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/92928/original/image-20150825-15896-1ar0fkw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/92928/original/image-20150825-15896-1ar0fkw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/92928/original/image-20150825-15896-1ar0fkw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/92928/original/image-20150825-15896-1ar0fkw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/92928/original/image-20150825-15896-1ar0fkw.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">Sunset over the Indian Ocean.</span>
<span class="attribution"><span class="source">NASA/ESA/G Bacon</span></span>
</figcaption>
</figure>
<p>With the ISS orbiting the Earth every 90 minutes, astronauts can see the Sun rise and set around 16 times every 24 hours. The dramatic views from the station display a rainbow-like horizon as the Sun appears and disappears beyond the horizon.</p>
<p>The changes in colour are due to the angle of the solar rays and their scattering in the Earth’s atmosphere. If similar jaw-dropping views can be seen from Earth, seeing our mother planet lit up in the rising Sun certainly adds to the intensity of the picture.</p>
<h2>3. Stars and the Milky Way</h2>
<figure>
<iframe src="https://player.vimeo.com/video/38409143" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Amazing sightings of distant astronomical objects as seen from the space shuttle.</span></figcaption>
</figure>
<p>From the ground, atmospheric conditions and light pollution affect our ability to see stars and other celestial bodies. As light travels through layers of hot and cold air, the bending of its rays render a flickering image of these distant objects, while atmospheric particles such as dust prevent from seeing fainter objects such as nebulae and galaxies.</p>
<p>The lack of an atmosphere at the orbiting altitude of the ISS allows the residents on the space station to see the stars, the Milky Way and other astronomical features with much greater clarity than is possible on Earth.</p>
<h2>4. Meteor showers</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/92916/original/image-20150825-17096-duu601.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/92916/original/image-20150825-17096-duu601.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/92916/original/image-20150825-17096-duu601.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/92916/original/image-20150825-17096-duu601.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/92916/original/image-20150825-17096-duu601.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/92916/original/image-20150825-17096-duu601.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/92916/original/image-20150825-17096-duu601.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">
<figcaption>
<span class="caption">The disintegration of a Perseid meteor photographed in August 2011 from the ISS.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Astronauts aboard the ISS can also witness the disintegration of meteoroids in the Earth’s atmosphere. Those small bodies are fragments detached from celestial bodies such as asteroids and comets. As they enter in the Earth’s atmosphere at great speed, the heat due to the body interaction with air rapidly destroys them. Whereas the chance of seeing them from the ground is very much weather dependent, being on the ISS guarantees the best seats to watch these shooting stars flaming across our planet’s sky.</p>
<h2>5. Auroras</h2>
<p>Also known as northern and southern lights, auroras are created when solar storms, consisting of large magnetised clouds of energetic particles launched from the sun, or strong <a href="http://www.swpc.noaa.gov/phenomena/solar-wind">solar wind</a>, interact with the Earth’s magnetic shield. Upon collision with the Earth, these solar streams energise particles within the planet’s magnetic shield.</p>
<figure>
<iframe src="https://player.vimeo.com/video/130263115" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Time lapses showing the ISS travelling through auroras.</span></figcaption>
</figure>
<p>When they enter the upper layer of the Earth’s atmosphere, these energetic particles excite nitrogen and oxygen atoms present at these altitudes. Then when they return from their excited state, these atoms emit light of different colours indicative of the amount of energy they absorbed. This typically produces green and red, ribbon-like curtains. </p>
<h2>6. Cosmic rays</h2>
<p><a href="http://helios.gsfc.nasa.gov/gcr.html">Galactic cosmic rays</a> aren’t really a phenomenon you can see. These energetic sub-atomic particles come from intense astronomical sources such as exploding stars or black holes. If they pass into the body they can damage tissue and break DNA, causing various diseases over the course of time.</p>
<p>Most cosmic rays do not penetrate in the thick atmosphere of the Earth. Since the ISS sits outside this protected zone, its astronauts are much more likely to be struck by the particles. Astronauts regularly see <a href="http://www.sciencedirect.com/science/article/pii/S0042698905006735">flashes of light</a> when they close their eyes, which is thought to be caused by cosmic rays interacting with body parts that play role in vision, such as the optic nerve or visual centres in the brain.</p>
<p>Solar storms, which have a strong magnetic structure, act as a shield against cosmic rays. A solar storm passing by the Earth can be indirectly witnessed by astronauts aboard the ISS via a drop in the count of cosmic rays, also known as the “<a href="http://science.nasa.gov/science-news/science-at-nasa/2005/07oct_afraid/">Forbush decrease</a>”. What a sensation it must be to “feel” a storm passing by the Earth’s system.</p><img src="https://counter.theconversation.com/content/46636/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Miho Janvier 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>Astronauts living on the ISS get to experience the wonders of the universe’s natural phenomena like no one else.Miho Janvier, Lecturer in Mathematics, University of DundeeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/66232012-04-23T20:29:54Z2012-04-23T20:29:54ZAn extragalactic mystery: where do high-energy cosmic rays come from?<figure><img src="https://images.theconversation.com/files/9853/original/9vpmjr5j-1335158346.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Knowing where cosmic rays don't come from brings scientists another step closer to determining their origin.</span> <span class="attribution"><span class="source">NSF/J. Yang</span></span></figcaption></figure><p>It’s been the defining question of high-energy astrophysics for the past century: where do <a href="http://en.wikipedia.org/wiki/Cosmic_ray">cosmic rays</a> come from?</p>
<p>New findings from the <a href="http://icecube.wisc.edu/">IceCube Neutrino Observatory</a> at the South Pole have brought us closer to understanding the origin of these strange “rays” – charged particles that originate somewhere beyond our planet and that reach Earth with varying energy levels and in different forms.</p>
<p>A <a href="http://icecube.wisc.edu/news/view/54">recent announcement</a> by IceCube scientists suggests the newly constructed observatory has found evidence allowing them to <a href="http://www.abc.net.au/science/articles/2012/04/19/3480435.htm">rule out gamma-ray bursts</a> – the most energetic explosions in the known universe – as the most likely source of the highest-energy cosmic rays.</p>
<p>This is big news, make no mistake. But to understand the significance of this finding, we first need to take a look at the history of cosmic-ray research.</p>
<h2>Cosmic(-ray) history</h2>
<p>Some 100 years ago, the pioneering Austrian physicist <a href="http://www.mpi-hd.mpg.de/hfm/HESS/public/hessbio.html">Victor Hess</a> jumped in a hot-air balloon and climbed to the dizzying height of 5.3km above the earth’s surface.</p>
<p>Why? Because he, as with many scientists of his day, was wondering where exactly <a href="http://en.wikipedia.org/wiki/Ionizing_radiation">ionising radiation</a> was coming from.</p>
<p>Ionising radiation is comprised of particles that can react with matter; radiation such as that seen in the fallout from the <a href="https://theconversation.com/topics/fukushima">Fukushima nuclear disaster</a>.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/9865/original/wh9ygs97-1335176090.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/9865/original/wh9ygs97-1335176090.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1040&fit=crop&dpr=1 600w, https://images.theconversation.com/files/9865/original/wh9ygs97-1335176090.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1040&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/9865/original/wh9ygs97-1335176090.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1040&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/9865/original/wh9ygs97-1335176090.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1307&fit=crop&dpr=1 754w, https://images.theconversation.com/files/9865/original/wh9ygs97-1335176090.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1307&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/9865/original/wh9ygs97-1335176090.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1307&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Victor Hess’s balloon trip was a foundation moment in the study of cosmic rays.</span>
</figcaption>
</figure>
<p>(It is important to understand, however, that the ionising radiation that was a mystery in the early 20th century is stopped by the Earth’s atmosphere. It was the by-products of the radiation’s interaction with the atmosphere that was being observed.)</p>
<p>Hess’s major achievement was to show that as altitude increases, so do the levels of ionising radiation – and so the radiation must have been coming from space. This radiation was thus given the title “cosmic rays” and Hess was awarded the 1935 Nobel Prize in Physics for his troubles.</p>
<p>Ever since, scientists such as myself have been wondering where these cosmic rays actually came from.</p>
<h2>What we know</h2>
<p>While we are still in the dark about some major aspects of the origins of cosmic rays, we’ve made considerable progress.</p>
<p>We know cosmic rays are made up of charged particles: primarily <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html">protons</a> (roughly 89%), helium (roughly 9%) and <a href="http://www.chem4kids.com/files/atom_electron.html">electrons</a> (roughly 1%) with heavier elements (up to iron) making up the other 1%.</p>
<p>We also know cosmic rays arrive at Earth with an impressive energy range: from millions of electron volts – an <a href="http://en.wikipedia.org/wiki/Electron_volt">electron volt (eV)</a> is the amount of energy gained by the charge of a single electron when it is moved across an <a href="http://en.wikipedia.org/wiki/Electric_potential">electric potential difference</a> of one volt – up to more than 10<sup>21</sup> eV (the number 1 with 21 zeroes after it!).</p>
<p>These 10<sup>21</sup> eV particles are the most energetic particles ever observed – subatomic particles with the energy of a vigorous tennis serve!</p>
<p>Given the huge energy range with which cosmic rays arrive at Earth, it seems clear we need several explanations for their origin.</p>
<h2>Some from the sun</h2>
<p>The sun supplies many of the low-energy cosmic rays seen on Earth, while sources within our galaxy probably make up most of the rest. The cosmic rays at intermediate energies are probably created through the explosion of dead stars (known as <a href="http://www.mso.anu.edu.au/%7Ebrian/PUBLIC/supernovae.html">supernovae</a>), their remnants and other detritus from their lives.</p>
<p>But there are still large gaps in our knowledge. There is precious little evidence about the exact site(s) of cosmic-ray acceleration – cosmic rays being sped up to extremely high energies – above what the sun or the Milky Way can produce.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/9867/original/8ngcz4mv-1335176526.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/9867/original/8ngcz4mv-1335176526.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/9867/original/8ngcz4mv-1335176526.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=720&fit=crop&dpr=1 600w, https://images.theconversation.com/files/9867/original/8ngcz4mv-1335176526.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=720&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/9867/original/8ngcz4mv-1335176526.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=720&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/9867/original/8ngcz4mv-1335176526.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=905&fit=crop&dpr=1 754w, https://images.theconversation.com/files/9867/original/8ngcz4mv-1335176526.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=905&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/9867/original/8ngcz4mv-1335176526.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=905&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 lowest-energy cosmic rays (yellow band) come from the sun, intermediate-energy cosmic rays (blue band) originate in our galaxy while the highest-energy cosmic rays (purple band) are extragalactic in origin.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>At modest energies, there is <a href="http://www.nature.com/nature/journal/v378/n6554/abs/378255a0.html">very good evidence</a> – from X-ray and radio telescopes – that the remnants of supernovae can accelerate cosmic-ray electrons. But we still have no strong evidence where cosmic-ray protons, which, you’ll recall, make up roughly 90% of cosmic rays, are accelerated, even in our own cosmic backyard.</p>
<p>And even after a century of intense study, we still don’t know the exact source of the highest-energy cosmic rays; subatomic particles with energies above about 10<sup>15</sup> eV. These particles are found above what is known as the “knee” of the cosmic ray spectrum (see image above) and are thought to come from extragalactic sources.</p>
<p>So, how do we go about determining the source of these high-energy cosmic rays, observationally? There are two methods: direct and indirect detection.</p>
<h2>Direct detection of cosmic rays</h2>
<p>Due to the fact cosmic rays are made up of charged particles, they are – unlike <a href="http://en.wikipedia.org/wiki/Photon">photons</a> (light particles) – deflected by ambient magnetic fields. As a result, the exact location of their acceleration is lost.</p>
<p>But the relative weakness of galactic and intergalactic magnetic fields implies this does not occur for sufficiently energetic cosmic rays – rays with energy levels above 10<sup>19</sup> eV.</p>
<p>Thus it was a great breakthrough in 2007 when the <a href="http://www.auger.org/">Pierre Auger Observatory</a> – a vast array of tanks and fluorescence (light) detectors dedicated to directly detecting cosmic rays at the highest energies – reported there was a <a href="http://arxiv.org/abs/0712.2843">statistically significant correlation</a> between cosmic rays and <a href="http://en.wikipedia.org/wiki/Active_galactic_nucleus">active galactic nuclei</a> – the centres of galaxies which contain supermassive black holes.</p>
<p>In other words, it appeared as if high-energy cosmic rays were coming from active galactic nuclei.</p>
<p>Unfortunately, this evidence is getting worse. While scientists at the Pierre Auger Observatory were sure their data were correct and their result was <a href="http://www.abc.net.au/science/articles/2012/04/11/3474740.htm">statistically significant</a>, in statistics, nothing is certain.</p>
<p>A small number of results will actually be a meaningless blip and, unfortunately for the researchers at the Pierre Auger Observatory, this result was one of them. Their signal is, sadly, disappearing into the statistical muck of random noise.</p>
<p>Therefore, for now, we need a non-interacting proxy for detecting cosmic rays: the <a href="https://theconversation.com/explainer-the-elusive-neutrino-431">neutrino</a>.</p>
<h2>Indirect detection of cosmic rays</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/9854/original/7ncy6k2g-1335159721.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/9854/original/7ncy6k2g-1335159721.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/9854/original/7ncy6k2g-1335159721.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=905&fit=crop&dpr=1 600w, https://images.theconversation.com/files/9854/original/7ncy6k2g-1335159721.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=905&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/9854/original/7ncy6k2g-1335159721.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=905&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/9854/original/7ncy6k2g-1335159721.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1138&fit=crop&dpr=1 754w, https://images.theconversation.com/files/9854/original/7ncy6k2g-1335159721.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1138&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/9854/original/7ncy6k2g-1335159721.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1138&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 two large columns containing cables for the IceCube experiment.</span>
<span class="attribution"><span class="source">Michael Ashley</span></span>
</figcaption>
</figure>
<p>Neutrinos are almost-massless, charge-less particles (their name means “little neutral one”) which are created in many particle interactions. You might remember that neutrinos were at the centre of the <a href="https://theconversation.com/neutrinos-and-the-speed-of-light-not-so-fast-3513">faster-than-light kerfuffle</a> earlier this year.</p>
<p>The neutrino’s lack of charge and mass, however, makes them incredibly difficult to detect and as a result, neutrino detectors have to be enormous.</p>
<p>As it turns out, one of the best detection mediums is the ice of Antarctica and so, to detect neutrinos from outer space, the one-cubic-kilometre IceCube observatory was built at the South Pole.</p>
<h2>The gamma-ray burst link</h2>
<p>For the vast majority of the past century, without enormous detectors such as IceCube, the only source of information about the acceleration of the highest-energy cosmic rays was purely theoretical.</p>
<p>Many of these theories have posited that mysterious bursts of gamma rays (photons with very high energies), called <a href="https://theconversation.com/flash-aah-aah-could-a-gamma-ray-burst-eradicate-all-life-on-earth-5291">gamma-ray bursts</a>, could provide a meaningful <a href="http://en.wikipedia.org/wiki/Flux">flux</a> of particles at the highest energies.</p>
<p>Gamma-ray bursts, the most energetic events in the known universe, are observed at a rate of a few per galaxy per century. They last from milliseconds to minutes and are followed by afterglows emitted at <a href="http://en.wikipedia.org/wiki/Electromagnetic_spectrum">X-ray to radio wavelengths</a>.</p>
<p>Despite their rarity, the vast expanse of our universe makes (or according to IceCube’s current research, made) these events a great potential source for the highest-energy cosmic rays.</p>
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<figcaption>
<span class="caption">Recent results suggest gamma-ray bursts aren’t responsible for creating high-energy cosmic rays.</span>
<span class="attribution"><span class="source">NASA (artist's conception)</span></span>
</figcaption>
</figure>
<p>We know that neutrinos are produced in the same interactions that should produce the gamma rays that give gamma-ray bursts their name. Hence, the theory goes, neutrinos should be observed from gamma-ray bursts.</p>
<p>Given this, it leaves particle physics in a precarious position, given that neutrinos from these gamma-ray bursts are not seen by IceCube.</p>
<h2>The importance of no neutrinos</h2>
<p>There are two schools of thought about the sources of cosmic rays at the highest energies. Either they’re created bottom-up – accelerated from lower energies, such as in gamma-ray bursts – or top-down – where more-energetic particles interact in some way and lose energy, creating cosmic rays.</p>
<p>Top-down models usually posit the existence of exotic <a href="https://theconversation.com/topics/dark-matter">dark matter</a> particles (although <a href="http://www.eso.org/public/news/eso1217/">recent results</a> suggest that even dark matter is not on as certain scientific footing as it once was).</p>
<p>The crux of the problem, really, is that other than active galactic nuclei and gamma-ray bursts, there are no known, credible sources that are abundant enough to create these high-energy cosmic rays.</p>
<p>This fact leads us to a startling conclusion: either the IceCube data is wrong (as with the Pierre Auger Observatory results, we might have seen a random fluctuation of the data masquerading as a statistically significant result), our understanding of gamma-ray bursts is wrong, or we have to appeal to a completely new paradigm of physics.</p>
<p>In this new paradigm, cosmic rays at the highest energies might be created by unknown particles, (possibly) under the influence of novel particle physics.</p>
<p>This could lead to this century’s Albert Einstein or Victor Hess showing the rest of us what we’ve been missing this whole time.</p>
<p>One thing’s for sure: this is a very exciting time to be a particle physicist. </p><img src="https://counter.theconversation.com/content/6623/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Jones 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>It’s been the defining question of high-energy astrophysics for the past century: where do cosmic rays come from? New findings from the IceCube Neutrino Observatory at the South Pole have brought us closer…David Jones, Postdoctoral Fellow in High Energy Astro-particle physicsLicensed as Creative Commons – attribution, no derivatives.