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Mothballed on NASA shelves were plans to see stars 13 billion years in the past. Now, a group of astronomers from the University of Texas at Austin want to brush up on ideas for a moon-based telescope and try to put them to good use.
The project was first unveiled over a decade ago because we didn’t have enough science about the first stars at that point. The Lunar Liquid-Mirror Telescope (LLMT) was initially coined when it was first proposed in 2008 by a team from the University of Arizona, and would feature a liquid mirror telescope operating from the surface of the Moon, far from any light pollution.
The proposed telescope, dubbed “Ultimately Large Telescope” by NASA Hubble Fellow and researcher Anna Schauer, would have a mirror 100 meters (300 feet) in diameter. It would operate autonomously from the lunar surface, receiving energy from a solar energy harvesting station on the moon that transmits data to a satellite in lunar orbit and from there to Earth.
Although the technology does not currently exist for such a device, and it would certainly be very expensive, astronomers say it would be worth it (even if the government might sing a different tune).
“Over the course of the history of astronomy, telescopes have become more powerful, allowing us to probe sources from successively earlier cosmic times, ever closer to the Big Bang,” said professor and team member Volker Bromm, a theorist who studied the first stars for decades. “The next James Webb Space Telescope (JWST) will reach the time when galaxies were first formed. But the theory predicts that there was an even earlier time, when galaxies did not yet exist, but where individual stars first formed: the elusive Population III stars. This “very first light” moment is beyond the capabilities of even the mighty JWST and instead requires a “definitive” telescope. “
Pop III stars, as they are sometimes called by astronomers, are made up entirely of primordial gas: helium, hydrogen and minimal amounts of lithium and beryllium. This means that the gas from which these stars formed had not been “recycled” (incorporated and then ejected) from previous generations of stars, but was uncontaminated material left over from the Big Bang.
Pop III stars are probably tens or 100 times larger than the Sun. They are a class of giant, hot, and bright stars that are thought to have existed in the early days of the universe. However, while researchers now strongly suspect they exist, we’ve actually never seen one, which is why the Ultimate Telescope would be useful.
Rather than coated glass, the telescope mirror would be made of liquid, as it is lighter, and therefore cheaper, to transport to the moon. It would also be a rotating tank of liquid, topped with a metallic – and therefore reflective – liquid (previous liquid mirror telescopes had used mercury). The tank would spin continuously, to keep the liquid surface in the correct paraboloid shape to function as a mirror.
The position of the telescope would be stationary, located inside a crater at the north or south pole of the Moon. To study the first stars, the Ultimately Large Telescope stared at the same patch of sky over and over, to collect as much light from them as possible.
“This first light moment is beyond the capabilities of current or near future telescopes. It is therefore important to think of the “definitive” telescope, capable of directly observing those first stars fleeing the boundaries of time. “
The telescope proposal will be published in an upcoming issue of The Astrophysical Journal.
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