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In the years to come, some truly impressive new generation telescopes will collect their first light. Between space telescopes like James webb and Nancy Grace Roman, and ground-based telescopes like 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 stars of population III, which are the first stars to be formed in the Universe. These stars are not observable in visible light and even new generation installations (like the ones mentioned above) will not be able to see them. But according to a team led by NASA Hubble Fellow Anna Schauer, the solution might be to build what she called the “Ultimately Large Telescope” (ULT) on the moon.
This idea, which was shelved by NASA ten years ago, was put forward by Schauer and his colleagues at the University of Texas at Austin in a recent article expected to be published in an upcoming issue of The astrophysical journal. It requires a liquid mirror telescope measuring 100 m (~ 330 feet) in diameter and powered by a solar panel that would operate autonomously on the lunar surface, relaying data to an orbiting satellite.
UT Austin theorist Professor Volker Bromm 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 the McDonald Observatory (which is overseen by UT Austin):
“Throughout 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] will reach the time when galaxies first formed.
“But the theory predicts that there was an even older era, when galaxies did not yet exist, but individual stars first formed – the elusive stars of Population III. This moment of “very first light” is beyond the capabilities of even the mighty JWST, and instead needs an “ultimate” 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). In the nuclei of these giant stars, heavier elements formed and became part of their outer layers which were then washed away when these stars died.
This process allowed the creation of heavy metals and silicates, which would allow the formation of planets. It also meant that all subsequent generations of stars had higher metal contents (aka metallicity), which astronomers use to determine star ages. By studying the stars of Population III, astronomers would reveal a lot about the evolution of our universe.
Unfortunately, these stars formed during what is known as the cosmic “dark age”, when the Universe was filled with clouds of gas that obscured visible and infrared light. This makes Population III stars invisible in almost all parts of the near infrared and radio spectrum that are currently inaccessible to even our most advanced instruments.
Fortunately, calculations made 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 – Regents Professor of Astronomy and Optical Sciences at the ‘University of Arizona.
After reviewing this proposal shortly thereafter, NASA chose not to proceed with the project. According to Niv Drory, principal investigator at the McDonald Observatory and co-author of the article, the science to back up the first stars did not exist at this point. However, subsequent research on Population III stars and NASA’s plans to return to the Moon (Project Artemis) make this proposal feasible again.
Similar to LLMT, ULT would rely on liquids rather than coated glass (making transport much cheaper to the Moon. One type of liquid would be arranged in a rotating tank while a second metallic liquid (like mercury, which is reflective) The vessel rotated continuously to keep the surface of the liquid 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 stationed in the Moon’s polar regions (north or south). In one of the many permanently shaded craters in these regions, the ULT would be free from radio or atmospheric interference.
On top of that, it would be able to watch the same area of sky continuously and collect as much light as possible in the near infrared spectrum. As Bromm summed it up:
“We live in a universe of stars. It is a key question of how the formation of stars began early in cosmic history. The emergence of the first stars marks a crucial transition in the history of the universe, when the primordial conditions set by the Big Bang gave way to ever-increasing cosmic complexity, ultimately giving life to planets, life and intelligent beings like us.
“This moment of first light is beyond the capabilities of current or future telescopes. It is therefore important to think of the “ultimate” telescope, the one that is able to directly observe these elusive first stars at the limit of time.“
The ultimate telescope of light is one of the many proposals for a lunar observatory. For example, several recommendations have been made for radio observatories to be stationed on the other side of the Moon. The absence of interference from terrestrial sources would not only be ideal for observing the invisible parts of the cosmos, but also in the search for extraterrestrial intelligence.
In addition, Dr Karan Jani and Professor Abraham Loeb – from the Laser Interferometer Gravitational Observatory (LIGO) and the Harvard-Smithsonian Center for Astrophysics (CfA), respectively – recently proposed that the Moon would also be a great location for a -Wave Lunar. Observatory for Cosmology (GLOC).
NASA is also planning to send a small satellite called the Dark Age Polarimetry Pathfinder (DAPPER) into lunar orbit in the coming years. This joint project between UC Boulder and the National Radio Astronomical Observatory (NRAO) will build on previous work by the Wilkinson Microwave Anisotropy Probe (WMAP) to explore the early Universe.
These and other proposals will have a chance to be implemented in the years to come. Beyond the return of astronauts to the Moon by 2024, the long-term goal of Artemis project is to establish a “sustainable lunar exploration” program. With this infrastructure in place, permanent facilities can be built that will help advance the science of space exploration!
Further reading: McDonald Observatory, arXiv
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