July 19, 2024

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A new way to detect the first stars in the universe

A new way to detect the first stars in the universe

Impression of a Pop III star falling toward a black hole. Credit: Space Telescope Science Institute/Ralph Crawford

Astronomers have long tried to discover the first stars in the universe, hypothetical stars called third-group stars, in the universe. It must have been composed only of the lighter elements, hydrogen and helium, and it must have been very large and very hot. Despite their size and temperature, they have not yet been discovered because they only occurred at the beginning of the universe, meaning they are at distances that cannot (yet) be seen with our telescopes.

Schematic of TDEs for Pop III stars. Credit: The Astrophysical Journal Letters (2024). doi: 10.3847/2041-8213/ad41b7

But now a team of astronomers led by Jin Lixin (University of Hong Kong) has devised a new way to observe them, at least to see signals from them. Supermassive black holes already existed at that time — roughly a few hundred million years after the Big Bang — as Webb’s observations have shown. We know from these black holes closest to Earth that sometimes a star can get very close, and then be completely pulled out and disappear into the black hole, which on Earth can be seen as a so-called black hole. Tidal disturbance occurred (TD). What if Pop III’s star disappeared into a supermassive black hole? Lexin and her team asked this question, and it appears that we can also see the TDE of the Pop III star, even though it occurs billions of light-years away (read: early).

TDEs of nearby supermassive black holes, in which “ordinary” stars are located, have been observed many times, and their properties are well known. lexin et al I think the Pop III TDEs are different and should be visible as infrared due to the expansion of the universe (NIR in the chart above). These TDEs should be visible using the James Webb Space Telescope (JWST) and the not-yet-launched Nancy Grace Roman Space Telescope (JWST). According to calculations, the Romans should have been able to see a few dozen of them annually.

You can read more about this in the professional article written by Rudrani Kar Chowdhury et al, Detection of star clusters III by JWST and Roman epoch tidal disturbance events, Astrophysical Journal Letters (2024).

source: University of Hong Kong.

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