Velocity dispersion
In
spectral lines
of a collection of objects; the more radial velocities one measures, the more accurately one knows their dispersion. A central velocity dispersion refers to the σ of the interior regions of an extended object, such as a galaxy or cluster.
The relationship between velocity dispersion and
spiral galaxies. For example, the σ found for objects about the Milky Way's supermassive black hole (SMBH) is about 100 km/s, which provides an approximation of the mass of this SMBH.[2] The Andromeda Galaxy (Messier 31) hosts a SMBH about 10 times larger than our own, and has a σ ≈ 160 km/s.[3]
Groups and clusters of galaxies have more disparate (contrasting in degree) velocity dispersions than smaller objects. For example, while our own
elliptical galaxies, by comparison, have an average σ ≈ 200 km/s.[7]
For spiral galaxies, the increase in velocity dispersion in population I stars is a gradual process which likely results from the near-random incidence of momentum exchanges, specifically dynamical friction, between individual stars and large interstellar media (gas and dust clouds) with masses greater than 105 M☉.[8] Face-on spiral galaxies have a central σ ≲ 90 km/s; slightly more if viewed edge-on.[9]
See also
- supermassive black holes
- elliptical galaxies
- spiral galaxies
References
- ^ Collins Dictionary of Astronomy, 2nd Ed.; Harper Collins Publishers; 2000; pp. 444, 449
- S2CID 15482979.)
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- doi:10.1086/313274.
- S2CID 62800506.)
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- doi:10.1086/145730.
- S2CID 119264732.)
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