A central massive object (CMO) is a high mass object or cluster of objects at the centre of a large

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or ''galaxy'', although, broadly speakin ...

, such as a galaxy or

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of memb ...

. In the case of the former, the CMO may be a

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical obj ...

, a nuclear star cluster, or even both together. The most massive galaxies are thought to always contain a supermassive black hole (SBH); these galaxies do not contain nuclear star clusters, and the CMO is identified with the SBH. Fainter galaxies usually contain a nuclear star cluster (NSC). In most of these galaxies, it is not known whether a supermassive black hole is present, and the CMO is identified with the NSC. A few galaxies, for instance the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...

and NGC 4395, are known to contain both a SBH and a NSC. Although this is suggestive that ''all'' galaxies have CMOs, and that a common mechanism of galaxy formation causes both,

ESA , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1 ...

MIRI ) , subdivision_type = Country , subdivision_name = , subdivision_type1 = State , subdivision_name1 = , subdivision_type2 = Division , subdivision_name2 ...

scientist Torsten Böker observes that some galaxies appear to have neither SBHs nor NSCs. The mass associated with CMOs is roughly 0.1–0.3% times the total mass of the galactic bulge.

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Bibliography

* * {{astronomy-stub Astrophysics Supermassive black holes Star systems

See also

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Bibliography