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We now know that most stellar systems have 2 or more stars orbiting each other. Do we know of any galaxies which have 2 or more super massive black holes orbiting each other? Is it possible?

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Yes, there are galaxies with two supermassive black holes in the center, see for instance 4C +37.11

Most likely such galaxies are formed by collision and merger of two galaxies, and their cores have not yet merged. Source

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  • $\begingroup$ Are they stable or are they destined to merge? What about their axis of rotation, are they parallel, if not, what happens where the jets collide? What are the effects in the region between the 2? $\endgroup$ – Bingohank Jul 31 at 22:32
  • $\begingroup$ Binary black holes are always losing energy to gravitational waves and are destined to eventually merge. Someone else may know the expected timescale for supermassive black holes orbiting at galactic-scale differences. $\endgroup$ – Mark Foskey Aug 1 at 2:45
  • $\begingroup$ I just added a link to one source with more details about the merger. I haven’t read through all the papers this article refers to, but they seem interesting and relevant, and might shed some more light into question about the eventual merger and its timescales $\endgroup$ – tuomas Aug 1 at 20:09
  • $\begingroup$ @Mark "Simple" calculations of the SMBH merger time result in times longer than the current age of the universe. Yet it appears that SMBH mergers have occurred, so the simple calculations aren't adequate. This is known as the final parsec problem. $\endgroup$ – PM 2Ring Aug 2 at 3:06

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