Free Astronomy Magazine May-June 2022

MAY-JUNE 2022 W ith this obser- vation, the NASA/ESA Hubble Space Telescope has established an ex- traordinary new benchmark: detecting the light of a star that existed within the first billion years after the Universe’s birth in the Big Bang (at a redshift of 6.2) — the most distant individ- ual star ever seen. This sets up a major target for the NASA/ ESA/CSA James Webb Space Telescope in its first year. [NASA, ESA, B. Welch (JHU), D. Coe and A. Pagan (STScI)] dividual Population III stars. In these remote times, however, at least two scenarios might have occurred that could delay the extinction of those stars, making them reach epochs (dis- tances) that can be in- vestigated by current instruments. The first scenario predicts that, in the extreme periph- eries of the first galax- ies, there may have remained clouds of primordial gas not enriched by the metals expelled by supernova ex- plosions typical of the innermost galactic regions. Population III stars may have grown in those clouds late enough that their light is still reach- ing us. The second scenario is pre- dicted by some models describing the formation of those stars, accord- ing to which the clouds of hydrogen and helium that forged more mas- sive stars might also have produced less massive stars with significantly longer life expectancies. stars. Those models also tell us that the larger the initial mass, the shorter the existence of the star. About Population III stars, their per- manence in the so-called Main Se- quence has probably not exceeded a few tens of millions of years. If we consider, as the most recent cosmo- logical models indicate, that the first stars of the universe should have ap- peared between 100 and 250 million years after the Big Bang, the obser- vation of Population III stars requires that we be able to reach the epoch when the universe was only about 300 million years old. Unfortunately, that era is hard to investigate be- cause it is characterized by the final phase of the so-called reionization of the universe, which transitioned the universe from a state of transparency to a state in which the first objects became visible by emitting electro- magnetic radiation. So far, the far- thest object astronomers have been able to prove the existence of is a very remote galaxy called GN-z11, lo- cated in time about 400 million years after the Big Bang. Therefore, it seems unthinkable to be able to observe in- ASTRO PUBLISHING