We are in the middle of a billion-dollar telescope building boom. The Giant Magellan Telescope, Thirty Meter Telescope, and Europe’s Extremely Large Telescope are all part of a new class of ground-based observatories that will peer farther through space and further back in time. First, we built big telescopes, and then we made the very large telescope, and now we are making extremely large telescopes. But really what it means, it’s about 10 times larger than any telescope we have today. And all this for our race to see the edge of the universe in the 2020s. But why now? How did we get here?
Race to See the Edge of the Universe – Giant Magellan Telescope
Typically, the size of the largest telescope on the earth doubles about every 40 years. Around 2000 there were groups around the globe who had just finished building telescopes of about 8 and 10 meters in diameter, and they recognized the technology could be used to make telescopes even larger. And that was about the time we discovered that as astronomers we have no idea what’s actually going on in the universe. I mean no idea in the sense that we figured out that 97% of the stuff in the universe can’t be seen and we don’t know what it is. So that was a good motivation to build bigger telescopes.
The technology got better for us to make this quantum jump from, you know, eight meters to 30-meter glass. This comes down to a few key elements. The first is a revolution in mirror size and design. The telescope performance is mostly driven by the size of the primary mirror. The bigger the primary mirror, the more light we can collect. That means we can go faint into the universe, you can look at smaller objects, more distant objects.
How we are preparing the Telescope?
The problem is you can’t make one single mirror any large than about 20 feet in diameter. There are just basic material properties in the glass that make it very difficult. So, we have to make mirror segments. We take the parent optical surface and kind of like with the biscuit cutter we cut it into seven circles. Then we make them to one combined parent optical surface that brings the light then to a single focus.
We have to then hold those mirrors in place on a large steel structure that’s stiff enough that it doesn’t shake in the wind, and it doesn’t sag under its own weight, and then it has to be precise enough to steer across the sky so that when we move to track the stars or the planets there’s no vibration. And we do that strangely enough by floating the entire telescope, entire 1,000 tons on a thin film of oil.
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The telescope simply floats on that in a way that’s completely frictionless. That’s the design for the Giant Magellan Telescope, whereas the E-ELT will take a slightly different approach. The original idea was to build, not a forty-meter diameter, but 100-meter diameter. And that was called the Overwhelmingly Large Telescope.
The engineers said “You know, this is really too much for us. The shape of the telescope has to be precise to few tenths of nanometers. So, the width of a hair across the entire forty-meter diameter of the primary, which is, actually, not even one single piece. It’s made of 798 individual smaller mirrors. Each of them needs to be polished, extremely accurate, and then controlled extremely accurate, to mimic this uniform surface at the nanometer level. This is all required to be accurate to Nano-level for our race to see the edge of the universe.”
These enormous precision machines will be built in some of the driest and most remote places on earth. Complementing space telescopes like Hubble and the soon to launch James Webb. “Hubble’s pictures have been fantastic, pioneering work. But, they are somehow they have been pushed to their limit. So, what we can expect from this 30-meter telescopes are to do exactly the same revolution, as Hubble did 20 years ago.
Challenges to be faced
One major challenge these ground-based scopes have to contend with is our planet’s atmosphere. The problem is the light from the stars that traveled for millions of years or sometimes billions of years through the universe and through the galaxy. When it hits our atmosphere the light kind of wiggles as it goes through. This is what gives the stars their classic twinkle, but it causes problems for astronomers who want super sharp images. This is where the next key advance comes in.
How the Telescope works
For our race to see the edge of the universe researchers have gone through many experiments. Recently over the last ten years, there’s been a lot of development, what is called adaptive optics. Here is how it works. Lasers from the telescope are shot into space, exciting the atoms in the sodium layer of the upper atmosphere and causing them to glow. That glow acts as an artificial star that astronomers can use to calculate the amount of atmospheric turbulence. Then, the mirrors will flex and deform by computer-controlled actuators to correct the blur to make sharp images. The challenge is we have to do that 500 to 1,000 times a second and we have to do that to about 1/20th of the wavelength of light in precision.
With unprecedented light-collecting capability and advanced optical geometry, these new observatories will tackle some of the most complex questions known to science. There’s been a lot of recent discovery of exoplanets. We can see, more or less, how distant they are from the planet. But we would like to understand how they are made of. Do they have an atmosphere which is similar to Earth, or not? How do you form all these planets? That’s only one aspect. Then, understanding how different galaxies formed and evolved across the cosmic time, we know for 13.5 billion years. And then, we can move to cosmology and understanding how dark matter and dark energy formed.
We are increasing the size so much and the capabilities are so powerful that it will open completely new discoveries in space. And we don’t really know where they will take us. And that’s to me the real beauty of these new facilities. The telescopes might seem big but they are really small compared to the size of the earth or the size of the universe.
So, if we can collect more light, we have a better chance of seeing those galaxies and black holes. Back when the universe was less than one billion years old. One of our key drivers is to look back and see when we transitioned from the universe being dark. The end of the dark ages to the first time it lit up, what we call cosmic dawn. That’s something that all astronomers would like to see and study the first light in the universe. The universe is a much bigger place than just what we experience here in our daily lives on the earth. So, the race to see the edge of the universe enriches our lives to simply understand that and to be aware of it.