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I know that astronomers have detected supermassive black holes in the early universe. What was the age of the universe at which these black holes were detected? In other words how long is it thought to take for these supermassive black holes to form and what are the mechanisms by which they formed, other than from supermassive stars?

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  • $\begingroup$ it is believed that they are formed from density fluctuation whatever it means less than a second after big bang and those that are less massive would have already evaporated by now. $\endgroup$
    – user6760
    Commented Aug 29, 2017 at 6:31

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The first supermassive black holes must have been formed earlier than about 750 million years after the big bang, since there is evidence for luminous quasars at redshifts of up to 7 and with likely black holes of a billion solar masses or more at their centres (e.g. Momjian et al. (2013).

The candidate mechanisms to produce such objects in a short period of time are hyper-Eddington accretion onto stellar black hole seeds; the direct collapse of large, primordial gas clouds into black holes; or the merger of stellar-sized black holes in dense clusters, followed by gas accretion. These possibilities are accessibly reviewed by Smith, Bromm & Loeb (2017).

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  • $\begingroup$ And also by the collapse of supermassive stars. Not for billion solar mass black holes but for those with a mass of hundreds or thousands of solar masses. $\endgroup$
    – Natsfan
    Commented Aug 29, 2017 at 19:17
  • $\begingroup$ @john I'm unaware of any work that suggests "supermassive" stars. Even for an initial "seed" of a thousand solar masses then super- or hyper-Eddington accretion is required to get a billion solar mass black hole in a few hundred million years. $\endgroup$
    – ProfRob
    Commented Aug 30, 2017 at 10:10
  • $\begingroup$ There was a recent study that indicated some early black holes may have been formed from supermassive stars. That report spurred my interest. phys.org/news/2017-03-supermassive-black-hole-limit.html $\endgroup$
    – Natsfan
    Commented Aug 30, 2017 at 13:16

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