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The Question

(Submitted February 16, 2011)

When the Universe had cooled after the Big Bang to the point where the first stars could form and given the sheer plentude of star forming materials that would have been available then, how massive would the first stars have been (compared to recently formed new massive stars) and what would the state today of the black holes they formed when they nova'ed ~12-13 billion years ago? How many black holes would have been formed in the first 100 million years after the first star formation?

The Answer

Thanks for your question. One key aspect to the early Universe is that the gas available to make stars did not have metals (which, to astronomers, mean every element except hydrogen and helium), since metals came later as a result of nuclear fusion in the stars themselves. This effectively made cooling of gas slow and is thought to have lead to a comparitively larger proportion of massive stars; some of which exceded several hundred times the mass of the sun. By comparison, we are only aware of stars reaching ~150 times the mass of the sun in the nearby Universe. The question about how many black holes would have formed is of significant debate and currently a topic of theoretical astronomy. It is likely, however, that in the early Universe, when the size of the Universe was small compared to today, many of these first black holes merged to give rise to increasingly more massive black holes. These massive black holes could then quickly "sink" to the centers of what would become the galaxies. This is a leading theory for how the supermassive black holes, commonly found at the centers of galaxies, formed over cosmic history.

(see, e.g., http://en.wikipedia.org/wiki/Supermassive_black_hole).

Bret & Antara
for Ask an Astrophysicist

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