Is there any naturally occurring event powerful enough that can cause a galaxy regardless of shape and size to divide itself into two or more smaller galaxies?

  • $\begingroup$ Maybe if it collides with two other galaxies simultaneously :-p $\endgroup$ – LocalFluff Jul 21 '15 at 4:51

Small galaxies (say of masses $\sim10^7M_\odot$) can be torn apart by stellar feedback, i.e. the energy provided by exploding stars in a starburst. Whether you want to call the debris galaxies is a matter of opinion, I suppose, but since these guys typically are satellites of larger galaxies, it will probably be torn completely apart by tidal forces, eventually accreting onto the larger one.

Large galaxies (say of masses $\sim10^{11}M_\odot$) are too massive to be split by feedback, but may lose matter (mostly gas, rarely stars) through large-scale outflows created by stellar feedback (or a quasar jet). However, when two large galaxies collide and merge, sometimes large chunk of gas, stars, and dark matter are slung out, which arguably could be called individual galaxies. Most of the matter of the two original galaxies become one, though.

  • $\begingroup$ Does the dark matter halo also split up and follow the debris in those small starburst galaxies? $\endgroup$ – LocalFluff Jul 21 '15 at 16:17
  • $\begingroup$ @LocalFluff: Yes, dark matter halos can also be torn apart by tidal forces. Since at a given point in space all matter experience the same tidal forces, this will not segregate the different components. However, in addition to the stellar feedback mentioned above, the gas can also be separated from the stars and the dark matter through ram pressure, i.e. the wind that the clump experiences when ramming through the gaseous part of a larger galaxy. $\endgroup$ – pela Jul 22 '15 at 10:40
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    $\begingroup$ Maybe my answer is a bit unclear: Small galaxies can blow out their gas. Since dark matter is gravitationally attracted to the gas, some of it will follow, but most will probably stay in a halo void of gas. This is probably the solution to the so-called "missing satellite problem", where large galaxies are surrounded by a large number of satellites that are difficult/impossible to detect. $\endgroup$ – pela Jul 22 '15 at 10:45

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