A telescope on the Moon to observe the mysterious stars of “population III”

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The youngest stars in the Universe are grouped into what astronomers call “population I». They are characterized by having many metallic elements due to the fact that they were formed from the death of other stars, which belong to the so-called «population II». However, these older stars, in theory, should not have little metallicity. But they do. That is why astronomers have thought that there must be a previous stellar generation, a «population III»From which new stars emerged. But, at the moment, there is still no proof of its existence, it is only a hypothesis.

These primeval stars were formed 13 billion years. They were born from hydrogen and helium, generating blue hypergiants extremely big, hot and, therefore, of short life, with masses of the order of several hundred times that of the Sun. However, the remains that may remain of these colossi are found in the confines of the universe, a place that is still very far for current terrestrial observatories. But what if we put the “Ultimate telescope” on the Moon?

This is the idea being considered by a group of astronomers at the University of Texas, at Austin, who have just dusted off an old project for a lunar telescope with a liquid mirror that NASA scrapped a decade ago. The team, led by Anna Schauer, a Hubble fellow, will publish her results soon in «The Astrophysical Journal“, Although the preliminary study can be consulted in” ArXiv».

Before there were galaxies

“Throughout the history of astronomy, telescopes have become more powerful, allowing us to probe sources from successively earlier cosmic epochs, increasingly closer to the Big Bang,” he explains in a release Volker Bromm, an astronomer at the University of Texas and one of the study’s authors. ‘The new James Webb Space Telescope – Hubble’s successor – will be able to see the moment when galaxies first formed. (…) But the theory predicts that there was an earlier time, when galaxies did not yet exist, where individual stars emerged: the elusive population III. This moment of ‘first light‘is beyond the capabilities of even the mighty James Webb, and that is why we need a’ ultimate ‘telescope.

According to the researchers’ calculations, the lunar liquid mirror telescope project could be able to see these stars. The original plan, proposed in 2008 by a team led by Roger Angel, from the University of Arizona, it was discarded because the science supporting the existence of this “population III” was so scant. But now there is much more evidence to support this hypothesis and “this telescope would be perfect for that problem,” he says. Niv Drory, a principal research scientist at the McDonald Observatory at UT Austin, and another of the study’s authors.

What would that liquid mirror telescope be like?

The lunar telescope would have a liquid mirror of 100 meters in diameter -80 meters more than what was proposed in the previous project-. It would work autonomously from the lunar surface, receiving power from a solar energy collection station on our satellite, and in turn transmitting data to a satellite in lunar orbit.

Instead of coated glass, the telescope mirror would be made of liquid, since it is lighter and cheaper to transport to the surface of the Moon. It would be something like a kind of giant rotating “jar”, topped by a metallic liquid – other similar telescopes use mercury– and therefore reflective. The continuous rotating motion would keep the liquid surface in the correct paraboloid shape to function as a mirror.

Recreation of the proposed lunar telescope – Roger Angel et al./Univ. of Arizona)

The location would be the north or south pole of the Moon, and would always look towards the same strip of space to collect as much light as possible. “This moment of first light is beyond the capabilities of current or near-future telescopes. Therefore, it is important to think of the ‘ultimate’ telescope, one that is capable of directly observing those elusive first stars at the edge of time, “says Bromm. And taking this lunar telescope out of the drawer could hold the key.

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