Scientists have found very bright source of light which they call quasar and the are found to be supermassive black holes. So these black holes are so massive that they cannot be formed by a supernova. So how are these formed?

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    $\begingroup$ This is actually an open question in astrophysics. No one has a definitive answer, though many ideas exist. $\endgroup$ – Kyle Kanos Nov 26 '14 at 3:36
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    $\begingroup$ Surprisingly, it doesn't look like this has even been mentioned here before, or on Astronomy. Nice question. $\endgroup$ – HDE 226868 Nov 26 '14 at 3:37

Nobody knows.

That's it, in a nutshell. However, there are some various ideas floating about. Here's a (long) list of some:

From this page:

  • Collapse of massive gas clouds
  • Merger of lots of stellar-mass black holes
  • Growth of a stellar-mass black hole to astronomical (pun intended) proportions

From Wikipedia:

  • Core collapse of a cluster of stars
  • Primordial black holes coalescing

From here:

  • Accretion of primordial gas left over from the Big Bang

From here:

  • The death of really, really massive stars (Note: This would only be the beginning of a supermassive black hole; much more accretion would have to take place. In fact, this can be said of many of the solutions presented.)

But the truth is (and I'll be blunt here) that scientists don't have as much evidence as they'd like for any of these ideas. There are lots of models (just see the ideas above) for the formation of these black holes based on observations of quasars, active galactic nuclei and normal galaxy centers, but it's difficult, if not impossible, to properly test them.

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    $\begingroup$ I'd add that we can adjust parameters for various models for the growth and mergers of these black holes, and this can lead to either underpredicting or overpredicting their abundance. So it's not a situation of "we can't explain where they come from" but rather "there are many ideas that work, we're not sure which most accurately depicts reality." $\endgroup$ – user10851 Nov 26 '14 at 14:55
  • $\begingroup$ @ChrisWhite Okay, I'll add something to that effect. $\endgroup$ – HDE 226868 Nov 26 '14 at 14:56
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    $\begingroup$ Another possible explanation: collapse of $\sim10^5$ solar mass star. $\endgroup$ – Kyle Kanos Nov 26 '14 at 15:09
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    $\begingroup$ How does the collapse of a $10^{5}M_{\odot}$ star make a supermassive black hole? This could only be part of a solution right? Supermassive blackholes are 10-10,000 times more massive than this. $\endgroup$ – Rob Jeffries Nov 26 '14 at 21:58
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    $\begingroup$ @RobJeffries Yes, it would only be the beginnings of a solution. Both the universetoday article and the paper Kyle Kanos cited say that these stars would only be the "seeds" of a supermassive black hole. $\endgroup$ – HDE 226868 Nov 26 '14 at 22:01

Normal black holes form from the mass of a dying star, so for a black hole to have more mass than the star it got it mass from something must be up. To understand why black holes in Quazars are so large, we need to understand what a Quazar is. Black holes often consume nearby stars, and during consumption, the stardust orbits the black hole and accelerates to speeds close to the speed of light. Friction with other stardust particles cause immense heat and emission of electromagnetic radiation. The black hole gains more mass by consuming nearby stars until it becomes big enough to make a real quazar, the kind that can be seen.

  • $\begingroup$ Don't know if it answers all but it is reasonable. Also to be able to consume so many other stars it must be in a particularly dense area, and thus mostly at the center of a galaxy. The biggest supermassive black hole (if I remember right) is about 10^11 solar masses. Can there be supermassive black holes (quasars) without a glaalaxies around, i.e., having consumed everything around it? $\endgroup$ – Bob Bee Jul 3 '16 at 21:19
  • $\begingroup$ No it is very doubtful that it can work like this without having very massive black hole seeds to begin with There is a fundamental problem with the growth timescale being limited by radiation pressure. 1 billion solar mass BHs are already present a billion years after the big bang. physics.stackexchange.com/questions/167250/… $\endgroup$ – Rob Jeffries Jul 4 '16 at 0:16

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