With today's announcement of the historic detection of gravitational waves from the merger of 36 solar mass and 29 solar mass black holes 1.3 billion light years away, one can not help but wonder how such a black hole binary system was formed.

Has there ever been any observation of a hypergiant (class 0 or Ia star) binary system in the optical or other EM radiation? I would expect that these observations would be rare give the short lifespan of these stars.

If a black hole binary formed from a binary of population 3 stars with masses over 600 solar mass, how long would one expect that they would remain in orbit around one another before they merge?

  • $\begingroup$ They are indeed very large compared to known stellar mass black holes, but I think the reason we haven't discovered more massive BHs in the past is that they are so hard to detect, they are very small in size and give off minimal radiation, the best way to see them is with their interaction with matter, something harder to see with stellar mass black holes. Over the lifetime of these black holes, its not implausible to think that they could have accreted a significant proportion of their mass. $\endgroup$
    – Dean
    Feb 11, 2016 at 19:50
  • $\begingroup$ dcc.ligo.org/LIGO-P1500262/public/main is an excellent reference on this topic. It appears that massive black hole binaries can form from low metallicity progenitor stars. In the case of GW150914, Z probably around 0.1-0.5 solar. $\endgroup$ Feb 11, 2016 at 20:38
  • $\begingroup$ Consider Eta Carinae. Massive hypergiant binaries are perfectly possible, although not likely. Note also that there are no more Population III stars, so mergers between black holes in hypothetical Population III binary systems likely happened a long time ago. $\endgroup$
    – HDE 226868
    Feb 11, 2016 at 21:14
  • $\begingroup$ Yeah, this black hole merger happened approximately 1 billion years ago but the last population 3 stars formed around 1 billion years after the big bang. $\endgroup$
    – Dean
    Feb 11, 2016 at 21:49
  • $\begingroup$ What if there are some black hole binaries from population 3 stars which take billions of years before they merge? $\endgroup$ Feb 11, 2016 at 22:09


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