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In the next few years, some fantastic new generation telescopes will collect their first light. Among space telescopes like James Webb is Nancy Grace Romanand ground-based telescopes such as the Extremely Large Telescope (ELT) and Giant Magellan Telescope (GMT), astronomers will be able to study aspects of the Universe that were previously inaccessible.
For example, there are Population III stars, which are the first stars to have formed in the Universe. These stars are not observable in visible light and even new generation structures (such as those mentioned above) will not be able to see them. But according to a team led by NASA Hubble Fellow Anna Schauer, the solution may be to build what he called the “Ultimately Large Telescope” (ULT) on the moon.
This idea, which was shelved by NASA a decade ago, was put forward by Schauer and his colleagues at the University of Texas at Austin in a recent paper that is expected to be published in an upcoming issue of The Astrophysical Journal. It requires a liquid mirror telescope measuring 100 m (~ 330 ft) in diameter and powered by a solar array that would operate autonomously on the lunar surface, relaying data to an orbiting satellite.
Professor Volker Bromm, a UT Austin theorist and co-author of the paper, has been studying the first stars to form in our universe for decades. As he explained in a recent press release from McDonald Observatory (which is overseen by UT Austin):
“Over the course of the history of astronomy, telescopes have become more powerful, allowing us to probe sources from successively earlier cosmic eras, ever closer to the Big Bang. The next James Webb Space Telescope [JWST] it will reach the time when galaxies were first formed. “
“But the theory predicts that there was an even earlier time, when galaxies didn’t exist yet, but where single 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. “
The current scientific consensus is that Population III stars formed a few hundred million years after the Big Bang (over 13 billion years ago). These stars were different from those that exist today, composed of hydrogen and helium and relatively short-lived (a few million years). Within the cores of these giant stars, heavier elements formed which became part of their outer layers which were then wiped out when these stars died.
This process allowed the creation of heavy metals and silicates, which would have allowed the formation of the planets. It also meant that all subsequent generations of stars had higher metal content (also known as metallicity), which astronomers use to determine stellar ages. By studying Population III stars, astronomers would reveal a lot about the evolution of our universe.
Unfortunately, these stars formed during what is known as the cosmic “Middle Ages”, when the Universe was filled with clouds of gas that obscured visible and infrared light. This makes Population III stars invisible in all parts of the near infrared and radio spectrum that are currently inaccessible to even our most advanced instruments.
Fortunately, the calculations performed by Schauer and his colleagues show that a liquid mirror telescope operating from the surface of the Moon would be able to study these stars. The concept, originally known as the Lunar Liquid-Mirror Telescope (LLMT), was first proposed in 2008 by a team led by Roger Angel, the Regents Professor of Astronomy and Optical Sciences at the University of Arizona.
After reviewing this proposal shortly thereafter, NASA chose not to take the project forward. According to Niv Drory, a senior researcher at the McDonald Observatory and co-author of the article, supporting science on the first stars did not exist at that point. However, subsequent research on Population III stars and NASA’s plans for the return to the moon (Project Artemis) make this proposal feasible once again.
Similar to the LLMT, the ULT would rely on liquids rather than coated glass (which makes transportation to the Moon much cheaper. One type of liquid would be placed in a rotating tank while a second metallic liquid (such as mercury, which is reflective) The tank would rotate continuously to keep the liquid surface in the correct parabolic shape to function as a mirror.
Similar to what NASA, ESA, China and other space agencies are planning – building a moon base in the South Pole-Aitken Basin – the telescope would be positioned in the Moon’s polar regions (north or south). Within one of the many permanently shaded craters in these regions, the ULT would be free of radio or atmospheric interference.
Furthermore, it would be able to continuously stare at the same point in the sky and collect as much light as possible in the near infrared spectrum. As Bromm summed up:
“We live in a universe of stars. It is a key question of how star formation began early in cosmic history. The emergence of the first stars marks a crucial transition in the history of the universe, as the primordial conditions established by the Big Bang gave way to ever-increasing cosmic complexity, ultimately bringing life to planets, life and intelligent beings such as we.
“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 Ultimate Light Telescope is one of the many proposals for a lunar observatory. For example, numerous recommendations have been made for radio observers to be stationed on the far side of the moon. The lack of interference from terrestrial sources would be ideal not only for the observation of invisible parts of the cosmos, but also in the search for extraterrestrial intelligence.
Additionally, Dr. Karan Jani and Prof. Abraham Loeb – of the Laser Interferometer Gravitational Observatory (LIGO) and the Harvard-Smithsonian Center for Astrophysics (CfA), respectively – recently proposed that the Moon would also be an ideal location for a Gravitational. Wave Lunar Observatory for Cosmology (GLOC).
These and other proposals will have the opportunity to be implemented in the coming years. In addition to returning astronauts to the Moon by 2024, the long-term goal of Artemis project is to establish a program of “sustainable lunar exploration”. Once this infrastructure is in place, it is possible to build permanent structures that will help advance the science of space exploration!
Further reading: McDonald Observatory, arXiv
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