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Using very high resolution computer simulations, it has been shown that stars born in the primordial Universe from the gravitational contraction of gigantic gas clouds that formed after the
Big Bang, may still survive to the present day. The research, published in the journal Science, was carried out by a team of researchers from Heidelberg University’s Centre for Astronomy, the Max Planck Institute for Astrophysics in Garching and the University of Texas at Austin.
This is a surprising result because models of the formation of the first generation of stars have always predicted that they would be enormous, hundreds of times the mass of the Sun, with a lifetime of only a few million years (if not less), and ending their lives as hypernovae.
These models, however, didn't take into account a property of accretion disks that form during the gravitational collapse of a new star. According to the new simulations, these disks can fragment if the rate of arrival of gas onto the disk exceeds the rate at which material can be accreted onto the central star.
If this happens, new mass concentrations result, that look like the arms of a spiral galaxy, about which independent gravitational collapse can occur.
Over very short timescales (see illustration) these develop into stars, that at least initially, will be gravitationally bound to that in the centre.
If this evolutionary scenario is confirmed, there are important implications: firstly, it implies that the early Universe was not populated exclusively by solitary super-massive stars, but rather by small groups of stars that also included stars of low mass. Secondly, the catastrophic collision between the members of close pairs could have generated X and gamma ray bursts that may be detected by new instruments in the near future. Lastly, due to the closeness of the stars (as little as an astronomical unit) some stars could be expelled from the group before accumulating very much mass from the accretion disk. Their resulting low mass would guarantee them a very long life, perhaps even as long as the 13 billion years that have elapsed since their formation.
If those low mass primordial stars took part in the formation of the first dwarf galaxies, that in turn merged to form galaxies like our own, then we might expect to find examples of this ancient population in the Milky Way, perhaps not even far from the Sun. The study of such a star would provide direct information on the physics and chemistry of the early Universe.
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