The Astronomer’s Holy Grail

Is that a planet, a galaxy or a Rosetta Stone? ichewmylips

A vital part of professional astronomy is collecting data using large telescopes. In many cases, these telescopes are national or international facilities, with time available to all through a competitive process.

As a result, astronomers spend much of their time writing “observing proposals”, in which they are given just a few pages of text to make the case to an expert panel that the telescope should be pointed at their particular star, galaxy or other celestial object.

In an effort to convince the panel a project is worthy of telescope time, astronomers inevitably resort to grand rhetoric, overstated claims and outright hyperbole to argue their idea is more important than all the proposals against which it is competing.

But amidst all these grandiose declarations, there are two phrases so overused that only the most foolhardy astronomers invoke them: the “Holy Grail” and the “Rosetta Stone”.

Astronomers try to avoid these particular clichés because most findings, even quite important ones, do not live up to such high expectations: only very rarely is a discovery truly transformational. But if I could somehow discover anything I wanted, what would I choose?

Just this once, I will break the unwritten rule of astronomy, and will dare to suggest a Holy Grail and a Rosetta Stone for the next few decades of astronomy.

Seeing the accelerating universe

We have known for more than 80 years that the universe is expanding. But there now seems to be clear evidence the universe is not only expanding, but is also accelerating in its expansion. As yet nobody has any good explanation for how this could be happening.

The most popular theory is that the universe is filled with dark energy, a mysterious unexplained force that is pushing the cosmos apart.

But it may be that our basic theories of cosmology and gravity are wrong, or that our measurements of the universe’s expansion are seriously flawed.

How to break this impasse? Simple. Measure the rate of the universe’s expansion, by observing distant galaxies seemingly race away from us at high speed, just as astronomers have done routinely for decades.

But make this measurement with exquisite accuracy, and then repeat it again 20 years later. With the next generation of extremely large telescopes and ultra-precise instrumentation, it should be possible to attain the Holy Grail of cosmology: to see individual galaxies pick up speed in real time as the universe accelerates.

This will be an extraordinarily challenging experiment – we will effectively need to build a cosmic radar gun that can measure a change in speed by just 0.5 km/h at a distance of 12 billion light years! But it will be worth the effort – the reward would be a spectacular verification of our modern view of a bizarre, accelerating, universe.

A Milky Way supernova

Big stars (much bigger than the sun) end their lives in catastrophic explosions called supernovae. A supernova is so bright that it outshines the entire galaxy of hundreds of billions of stars in which it’s embedded. But the extreme brightness of these supernovae is offset by the very large distances from us at which they usually occur.

Frustratingly, we haven’t seen a supernova in our own Milky Way Galaxy since the year 1604, and the telescope was invented in 1608! Studies of other galaxies suggest that a galaxy like ours should host a supernova once every 50-100 years.

Indeed many supernova explosions have probably occurred in the Milky Way over the last 400 years, but they were probably buried deep within dark, thick clouds of dust, and so went unnoticed.

And so astronomers wait patiently for the big one – a supernova explosion on our doorstep. When this eventually happens, you won’t need a telescope to see it. A nearby supernova would be so bright you would be able to see it in broad daylight; at night, it would cast a shadow and would be bright enough to read by.

This exciting event will transform astronomy. Some astronomers will point their telescopes at the explosion to study it in more detail and to watch the stellar debris expand and gradually fade. Others will pore over historical records and measurements of the star that died, looking for vital clues to its impending doom in old data, which we then might be able to apply to future supernovae.

And yet more astronomers will begin running powerful simulations of exploding stars, in an attempt to explain the unfolding story and to predict key observations that would need to be made in the coming weeks and months.

Perversely, astronomers often express genuine concern as to the problems a Milky Way supernova would create. Modern telescopes are designed to study very faint objects – a nearby supernova would be so bright that it would be difficult to make accurate measurements. But no doubt when the big moment arrives, solutions will be found.

A Milky Way supernova will answer a huge number of questions about how the most massive stars end their lives, but will inevitably raise many more. Dare I say it: a Rosetta Stone?

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