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I Are there galaxies with 2 cores?

  1. Dec 11, 2017 #1
    When discussing about galactic 'collisions' and mergers, such as the predicted future encounter between the Milky Way and Andromeda, it is often said that actual collisions among stars are extremely unlikely, it's just that the mutual gravitational influence of both galaxies on each other will gradually deform, distort, stretch or squeeze the galaxies' shapes, they will gradually engage in a gravitational dance around common centers of gravity, and slowly, if the gravitational attraction is strong enough to maintain the bond, the two structures will eventually evolve into some new shape as a new single and larger galaxy.

    Assuming that the galactic cores (say both include a super-massive black hole) are following paths far from heading to each other head-on, they will also enter a gravitational dance around a common center of gravity. And all the stars from both galaxies would get involved into a highly complex motion affected by the common center of gravity of both galactic centers, and possibly by each of them individually if they pass close enough to any of them. This could in principle last for billions of years before the two cores get closer and closer to each other and finally merge into a new single galactic core, combining the mass of the two previous cores.

    My question is, have we observed any such galaxies which display 2 separate cores resulting from a relatively recent merger? and if so, how do they look like? how they behave? what are their most interesting features?
    And in case we have not detected any such dual-core galaxies, what would explain that fact? Wouldn't it be natural to expect that such galaxies must be out there in the right environments?

    TX!
     
  2. jcsd
  3. Dec 11, 2017 #2

    Borg

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  4. Dec 11, 2017 #3

    Vanadium 50

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    I do not believe we have. M31 has a double nucleus, but simulations show it's much more likely to have only a single SMBH at point "P2". The reason is that the lifetime of such a two core system is exceedingly short before they merge.
     
  5. Dec 12, 2017 #4
    Isn't that based purely on observation?

    As far as I understand, astrophysicists are stuck on the maths of what actually makes them merge. I was under the impression that SMBHs fall into each other by eating material by ejecting it, both alter it's momentum allowing them to fall into lower orbits. The linked article indicates that when they get within a few light years of each other, all of that material is gone though, no one is sure how they get any closer other than by gravitational waves, which are negligible at those distances.
     
  6. Dec 13, 2017 #5

    stefan r

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    Antenna galaxies ngc4038 and ngc 4039

    220px-Antennae_Galaxies_NGC4038_NGC4039_Goran_Nilsson_%26_The_Liverpool_Telescop.jpg
    The mice galaxies are not yet merged
    300px-Merging_galaxies_NGC_4676_%28captured_by_the_Hubble_Space_Telescope%29.jpg

    My impression was that the space with few stars was the core. That would be 2 black holes inside of 1 merged core.
     
  7. Dec 14, 2017 #6

    Vanadium 50

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    I think its closer than that. In cores the distances between stars are measured in light-minutes or hours, not years. You can get quite close before you run out of stars to eject. But even if it were light years, on galactic scales, I would say two SMBH's within even a few light years of each other in the center of the core means you have one core, not two. Where you draw the "edge" of the core is not well defined, but for any reasonable definition, the core is dominated by stars and not their SMBH's.
     
  8. Dec 15, 2017 #7
    Thanks for all the answers
     
  9. Dec 20, 2017 #8
    Glad to know about this. Thank you so much for sharing.
     
  10. Dec 20, 2017 #9

    mfb

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    It is called final parsec problem - a few light years are right.
     
  11. Dec 22, 2017 #10
    wow nice! Thanks for placing the link here.
     
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