I've read many times that every galaxy contains a black hole at the center. So is the creation of a galaxy linked to black holes?
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1$\begingroup$ Not every galaxy has a black hole in the center. The central massive object for some galaxies are nuclear star clusters. $\endgroup$– Sir CumferenceSep 12, 2016 at 12:02
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$\begingroup$ Possible duplicate of Which came first: black holes or galaxies? or Supermassive black holes at the center of galaxies $\endgroup$– called2voyage ♦Sep 12, 2016 at 13:51
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1$\begingroup$ And some galaxies contain neither a central black hole nor a nuclear star cluster. $\endgroup$– Peter ErwinSep 12, 2016 at 15:20
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$\begingroup$ @PeterErwin Is there something else? Or are you saying that there doesn't necessarily have to be a massive object at the center of the galaxy to form? $\endgroup$– El BromistaSep 12, 2016 at 23:30
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$\begingroup$ @ElBromista: The latter. To give a local example, both the Large and Small Magellanic Clouds lack central massive objects. $\endgroup$– Peter ErwinSep 13, 2016 at 6:54
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2 Answers
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Firstly, observation supports that:
black holes are present in essentially every galaxy that has a bulge component
So, we can say a lot of galaxies have central black holes. But there are some type of galaxies which do not have a bulge, such as dwarf galaxies. For those we can not be sure if there is a black hole in the centre.
The link between the central super massive black holes (SMBH) and the host galaxies are build because people find a tight correlation between the mass of the SMBHs and the stellar mass of the bulge of the host galaxies. Thus, it's natural to think that there might be an relation in which the SMBHs and the host galaxies are effecting each other while they evolve.
Actually, nowadays people find the truth is much more complicated. This is still quite a hot research topic in astrophysics.
For more information, you can check this annual review paper: https://arxiv.org/abs/1304.7762
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$\begingroup$ Exactly, we're not sure about dwarfs; and by number dwarf galaxies are the most abundant. So I think "almost every galaxy" is a grave overstatement $\endgroup$– user1991Sep 21, 2016 at 18:51
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$\begingroup$ Note that it states "that has a bulge", dwarf galaxies do not have bulges. $\endgroup$– CyTexMar 24, 2021 at 20:49
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Most of the galaxies are believed to host a super massive black hole. The black hole in return has a dramatic impact on the evolution of the galaxy, an effect usually called "AGN feedback". Quoting W. Ishibashi, A. C. Fabian:
Active Galactic Nuclei (AGN), regions of extremely high luminosity at the centers of some galaxies, are thought to radiate due to accretion onto a supermassive black hole. This emitted radiation, or feedback, sends energy into its environment and influences the evolution of the host galaxy. The details of this feedback are not well understood. We do, however, observe several relationships between properties of the host galaxy and the central black hole — the most prominent of which is the M-sigma relation. This empirical correlation states that the black hole mass (M) scales as the fourth power of the velocity dispersion (sigma) of stars in the galactic bulge. Clearly, there is some connection between the evolution of the black hole and that of its host galaxy.
The topic of understanding how the supermassive black hole form in the first place, evolve and interact with their galaxy is still in debate among the scientific community, so it is impossible to fully answer your question yet.
