Sunday , December 5 2021

Can a giant lunar telescope reveal the very first stars?


A team of astronomers is reviving the idea that NASA set aside a decade ago in which a giant observatory on the Moon would be installed. Called the “Last Great Telescope,” the facility would easily surpass all other telescopes in its class and objects that predicted theories but had never been seen before.

A large liquid mirror telescope installed on the surface of the moon can perform a task that no other telescope can do: search for the signs of the first stars in the universe. Even the very powerful James Webb Space Telescope, which is scheduled to launch on October 31, 2021, will not be able to see the first stars.

So say astronomers at the University of Texas at Austin, who have detailed the arguments in an article to be published in a future issue of the Astrophysical Journal (prepress is available on arXiv).

Conceptual image of the Last Great Telescope.  The version proposed by the authors of the new study would be five times larger than this.  (Image: Credit: Roger Angel et al./Arizona University) Conceptual image of the Last Great Telescope. The version proposed by the authors of the new study would be five times larger than this. (Image: Credit: Roger Angel et al./Arizona University)

The concept dates back to 2008, when a team of astronomers at the University of Arizona proposed a telescope for the liquid mirror of the moon. NASA soon flirted with the idea, but eventually abandoned the concept because important science could have been with the stars of Population III — the first stars to appear in the universe. A telescope on the moon would be able to look into space without being affected by atmospheric effects and light pollution.

“Throughout the history of astronomy, telescopes have become more powerful, allowing us to study sources from successive cosmic times – those closer to the Big Bang,” said Volker Bromm, author of the article, in a University note. Texas McDonald Observatory. “The next James Webb space telescope will reach the time when galaxies were created.”

The problem is that JWST – as powerful as it is powerful – will not be able to detect smaller, darker objects that existed before galaxies were created, that is, Pop III stars. The moment of “first light” is beyond the capabilities of the powerful JWST, and instead it needs a “final” telescope, ”Bromm said.

Pop III stars formed hundreds of billions of years later from the Big Bang from a mixture of hydrogen and helium gas. The theory suggests that they were tens and hundreds of times larger than our Sun, but even then it does not match the size and brightness of an entire galaxy. Thus, Pop III stars have escaped perception.

That being the case, the authors of a new study led by NASA Hubble member Anna Schauer say that Pop III stars should be identified. We just have to spot their cubs, who will take on the appearance of “minihalos”. Early stars were born within tiny proto-galaxies, but the brightness of these objects is “too weak to detect even in the longest periods of exposure,” as the authors write in their paper.

“Our galaxy near Andromeda has about a trillion stars, and we can only see it with the naked eye in very dark places on Earth,” Schauer explained in an email. “These first small galaxies have between 10 and 1,000 stars, and they are much farther away – it has taken more than 13 billion years for light to reach Earth.” The two factors play a role, and we expect the minihalos to be 100 trillion times smaller than Andromeda. ”

By studying the stars of Pop III, we can study the conditions of the initial universe, he added.

“In the early universe, before the creation of these first stars, visible matter was composed only of hydrogen and helium. Stars are needed to “grow” higher elements that are essential to life, such as oxygen and carbon, “Schauer said.” We’re doing computer simulations to better understand Pop III stars, but we’re still not sure how massive and large those first stars and sets were. they were formed into larger or smaller ones. These questions can be answered with observations. “

That’s where the moon observatory can help. And, in fact, Schauer and his colleagues corrected the numbers because the mirror telescope must have been large enough on the surface of the moon. Niv Drory, the author and chief research scientist at the McDonald Observatory, said the proposed Last Great Telescope is “perfect” for the challenge.

Located at the north or south pole of the moon, the stationary mirror would measure 328 feet (100 meters). The telescope would be autonomous and powered by a nearby solar power plant. The observatory would transmit the data to a satellite in orbit around the moon.

The mirror of the telescope would be made of liquid, rather than glass (this solution is lighter and cheaper in terms of transportation). The mirror should rotate continuously to keep the liquid surface in a parabolic shape. A metallic liquid would form the top layer of the mirror to provide the required reflectivity. To prevent excessive heat from ruining the show, the telescope would be built inside an impact crater and placed inside a permanent shade.

The authors write, however, that “it is not clear what effect the moon’s dust would have on the instrument and observations.”

Looking at the cosmos, the Last Great Telescope would be fixed in a single spot on the sky to absorb as much light as possible, as it seeks minihalos in near-infrared and extreme red changes (objects that change to very red light). the farther we look, the deeper we see). As the authors mention in their paper, minihalos should create a distinctive signature, so they should be “unambiguously identified”.

Of course, we wouldn’t look directly at the Pop III stars, but we would look at their formation sites – a sort of smoking gun for their existence and certainly the next best thing.

Looking ahead, Schauer is pleased with the commercialization of JWST, which will allow scientists to study the first universe, including the first generation of stars that appeared after the formation of Pop III stars.

“For the future, I hope theorists and observers will work together to develop more technology for this lunar telescope,” he said. “I also hope that humans will return to the Moon to set up a site where ULT can be built.”

It is not the only proposal to build a large telescope on the Moon. NASA’s JPL robotics robot Saptarshi Bandyopadhyay explained the view of a lunar observatory that would be built inside a large impact crater. Unlike the last Great Telescope (which will search for sources of infrared light), the Lunar Crater Radio Telescope would be a long-wave ultraviolet radio telescope capable of detecting some of the weakest (and farthest) signals traveling through space. Bandyopadhyay’s project is in the first phase of NASA’s Innovative Advanced Concepts (NIAC) program.

Maybe one day we’ll finally see a NASA NIAC phase for the big telescope. The first stars are increasing their patience.

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