Central massive object

Short description: Central object of a galaxy

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The star-like nucleus at the centre of this edge-on spiral galaxy, NGC 4244, is a central massive object.

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A central massive object (CMO) is a high mass object or cluster of objects at the centre of a large star system, such as a galaxy or globular cluster. In the case of the former, the CMO may be a supermassive black hole, a nuclear star cluster, or even both together.[1]

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.[2] A few galaxies, for instance the Milky Way and NGC 4395, are known to contain both a SBH and a NSC.[3] The co-existence of both types of central massive objects was quantified in 2009.[4] Subsequently, a scaling relation between the mass of the supermassive black hole and the mass of the nuclear star cluster was discovered in 2016.[5]

Although this is suggestive that all galaxies have CMOs, and that a common mechanism of galaxy formation causes both, ESA MIRI scientist Torsten Böker observes that some galaxies appear to have neither SBHs nor NSCs.[6]

The mass associated with CMOs is roughly 0.1–0.3% times the total mass of the galactic bulge.[2]

## See also

* Core collapse (cluster)
* Galactic Center
* Stellar dynamics

## References

1. ↑ Böker 2010a, p. 61.
2. ↑ 2.0 2.1 Merritt, David (2013). Dynamics and Evolution of Galactic Nuclei. Princeton, NJ: Princeton University Press. https://openlibrary.org/works/OL16802359W/Dynamics_and_Evolution_of_Galactic_Nuclei.
3. ↑ Nishiyama, S.; Schödel, R. (2012). "Young, Massive Star Candidates Detected throughout the Nuclear Star Cluster of the Milky Way". Astronomy & Astrophysics 549: A57. doi:10.1051/0004-6361/201219773. Bibcode: 2012yCat..35490057N.
4. ↑ Graham, A. W.; Spitler, L. R. (2009). "Quantifying the coexistence of massive black holes and dense nuclear star clusters". Monthly Notices of the Royal Astronomical Society 397 (4): 2148–2156. doi:10.1111/j.1365-2966.2009.15118.x. Bibcode: 2009MNRAS.397.2148G.
5. ↑ Graham, A. W. (2016). "Black hole and nuclear cluster scaling relations: Mbh ∝ Mnc2.7±0.7". Proceedings of the International Astronomical Union 312: 269–276. doi:10.1017/S1743921315008017. Bibcode: 2016IAUS..312..269G.
6. ↑ Böker 2010b, p. 103.

### Bibliography

* de Grijs, Richard; Lépine, Jacques R. D., eds (2010a). "Nuclear star clusters". Star Clusters (IAU S266): Basic Galactic Building Blocks Throughout Time and Space. IAU symposium and colloquium proceedings. 266. Cambridge University Press. ISBN 9780521764995.
* Macchetto, F. Duccio, ed (2010b). "Young Massive Star Clusters in the Era of the Hubble Space Telescope". The Impact of HST on European Astronomy. Astrophysics and Space Science Proceedings. Springer Science & Business Media. ISBN 9789048134007.

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