Population III stars

From Academic Kids

Population III stars are a hypothetical population of extremely massive stars that are believed to have been formed in the early universe. They have not been observed directly, but are thought to be components of faint blue galaxies. Their existence is necessary to account for the fact that heavy elements, which could not have been created in the Big Bang, are observed in quasar spectra as well as the existence of faint blue galaxies. It is believed that these stars triggered a period of reionization.

Current theory is divided on whether the first stars were very massive or not. One theory, which seems to be borne out by computer models of stellar evolution, is that with no heavy elements from the Big Bang, it was easy to form stars much more massive than the ones visible today. Typical masses for population III stars are believed to be about several hundred solar masses, which is much larger than current stars. This also conveniently explains why there have been no low-mass stars with zero metalicity observed. Modifications to this theory have shown that stars this massive may not in fact be able to form, and will have roughly 100 solar masses instead. Confirmation of these theories awaits the advent of NASA's James Webb Space Telescope.

The greatest mass of star which may form today is about 110 solar masses. Any attempt to form a star greater than this results in the resulting protostar blowing itself apart during the initial ignition of nuclear reactions. Without enough carbon, oxygen and nitrogen in the core, however, the CNO cycle could not begin and the star would not go nuclear with such enthusiasm. Direct fusion through the proton-proton chain, however, does not proceed quickly enough to produce the copious amounts of energy such a star would need to support its immense bulk. The end result would be the star collapsing into a black hole without ever actually shining properly. These stars, if through new physics we do not yet know much about, were able to form properly then their lifespan would be extremely short, less than one million years certainly. As they can no longer form today, observing one would require us to look to the very edges of the observable universe. Seeing this distance while still being able to resolve a star could prove difficult even for the James Webb Space Telescope.

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Template:Star-stubfr:Étoile de population III

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