What Does the Universe Do When We’re Not Looking?
Some of the greatest discoveries in astronomy have been made by watching how the skies change over time. Today we talk about these techniques, and an observatory that will revolutionize time-based astronomy.
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Team: Fraser Cain – @fcain
Jason Harmer – @jasoncharmer
Chad Weber – firstname.lastname@example.org
Created by: Fraser Cain and Jason Harmer
Edited by: Chad Weber
Music: Left Spine Down – “X-Ray”
If you follow some of my other shows, like Astronomy Cast and the Weekly Space Hangout. Of course you do, what a ridiculous thing to say… “if”. Anyway, since you follow those other shows, you know I’m currently obsessed with an upcoming observatory called the Large Synoptic Survey Telescope.
Obsessions are best when they’re shared. So today, I invite you to become as obsessed as I am about the LSST.
In the past, astronomers focused on building bigger telescopes at more remote locations so they could peer more deeply into the past, to resolve the faintest objects, to see right to the edge of the observable Universe.
But there’s a whole other dimension to the Universe: time. And by taking advantage of time, astronomers have made some of the most momentous discoveries in the history of astronomy.
The Large Synoptic Survey Telescope is all about time. Watching the sky over and over, night after night, watching for anything that changes.
First, let’s talk about some of the kinds of discoveries that can be made when you’re watching the sky for changes.
Perhaps the best example of this is the Mira variable. These are red giants at the very end of their stellar evolution, almost out of usable hydrogen to burn in their cores. As their stellar flame flickers out, the light pressure can no longer hold against the gravity pulling the star inward. The star compresses in on itself, raising the temperature and pressure, allowing more fusion. It flares up again, and brightens in our sky.
Astronomers discovered that there’s a very specific relationship to the brightness and rate that this brightening happens. In other words, if you know how often a Mira variable flares up, you know how intrinsically bright it is. And if you know how bright it is, you can calculate how far away it is. Even in other galaxies.
That’s what Edwin Hubble did when he surveyed Mira variables in other galaxies. He discovered that most galaxies are actually speeding away from us in all directions, leading to the theory of the Big Bang.
Thanks to time, we understand that we life in an expanding Universe that originated from a single point, 13.8 billion years ago.
Let me give you another example: the discovery of gamma ray bursts. In the 1960s, the US launched a group of satellites as part of the Vela Mission. They had no astronomical purpose, they were designed to watch for the specific gamma ray signature from an unauthorized nuclear weapons test. But instead of nuclear explosions, they detected massive blasts of gamma radiation coming from deep space. These blasts only last for a few seconds and then fade away, leaving a faint afterglow that also fades.
We now know that gamma ray bursts mark the deaths of the largest stars in the Universe, and the formations of new black holes. Other gamma ray bursts signal the collisions of exotic stellar remnants, like neutron stars and white dwarfs.
I can give you many more examples, where the dimension of time lead to a discovery in astronomy:
In 1930, Clyde Tombaugh compared pairs of photographic plates, switching back and forth over and over, looking for any object that moved position. This was how he discovered Pluto. In fact, this same technique is used by astronomers to find other dwarf planets, asteroids and comets to this day.
Astronomers return again and again to galaxies in the night sky, looking for any that have a new star in them. This is a tell tale sign of a supernova, the explosion of a star much more massive than our Sun. Some of these supernovae allowed astronomers to discover dark energy, that the expansion of the Universe is accelerating.
This is what time can help us discover.
Now, on to the Large Synoptic Survey Telescope. The observatory is currently under construction in north-central Chile, where many of the world’s most powerful telescopes are located.
Its main mirror is 8.4 meters across. Just for comparison, ESO’s Very Large Telescopes are 8.2 metres across. The Gemini Observatories are 8.1 metres across. The Keck Observatory is 10 metres wide. What I’m saying here, is that the LSST is plenty big.