{{Short description|Central object of a galaxy}} {{Infobox | name = NGC 4244 | image = 250px | caption = The star-like nucleus at the centre of this edge-on spiral galaxy, NGC 4244, is a central massive object. }}
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.{{sfn|Böker|2010a|p=61}}
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.<ref name=DEGN>{{cite book|last=Merritt|first=David|author-link=David Merritt|title=Dynamics and Evolution of Galactic Nuclei|year=2013|publisher=Princeton University Press|location=Princeton, NJ|url=https://openlibrary.org/works/OL16802359W/Dynamics_and_Evolution_of_Galactic_Nuclei}}</ref> A few galaxies, for instance the Milky Way and NGC 4395, are known to contain both a SBH and a NSC.<ref>{{cite journal|author1=Nishiyama, S.|author2=Schödel, R.|title=Young, Massive Star Candidates Detected throughout the Nuclear Star Cluster of the Milky Way|year=2012|journal= Astronomy & Astrophysics|volume=549|pages=A57|arxiv=1210.6125|bibcode=2012yCat..35490057N|doi=10.1051/0004-6361/201219773|s2cid=17865037 }}</ref> The co-existence of both types of central massive objects was quantified in 2009.<ref>{{cite journal|author1=Graham, A. W.|author2=Spitler, L. R.|title=Quantifying the coexistence of massive black holes and dense nuclear star clusters|year=2009|journal=Monthly Notices of the Royal Astronomical Society|volume=397|issue=4|pages=2148–2156|arxiv=0907.5250|bibcode=2009MNRAS.397.2148G|doi=10.1111/j.1365-2966.2009.15118.x}}</ref> Subsequently, a scaling relation between the mass of the supermassive black hole and the mass of the nuclear star cluster was discovered in 2016.<ref>{{cite journal|author1=Graham, A. W.|title=Black hole and nuclear cluster scaling relations: M<sub>bh</sub> ∝ M<sub>nc</sub><sup>2.7±0.7</sup>|year=2016|journal=Proceedings of the International Astronomical Union|volume=312|pages=269–276|arxiv=1412.5715|bibcode=2016IAUS..312..269G|doi=10.1017/S1743921315008017}}</ref>
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.{{sfn|Böker|2010b|p=103}}
The mass associated with CMOs is roughly 0.1–0.3% times the total mass of the galactic bulge.<ref name=DEGN/>
== See also == * Core collapse (cluster) * Galactic Center * Stellar dynamics
== References == {{reflist}} === Bibliography === {{refbegin}} * {{cite book|title=Star Clusters (IAU S266): Basic Galactic Building Blocks Throughout Time and Space|series=IAU symposium and colloquium proceedings|issn=1743-9213|volume=266|editor1-first=Richard|editor1-last=de Grijs|editor2-first=Jacques R. D.|editor2-last=Lépine|publisher=Cambridge University Press|year=2010a|isbn=9780521764995|author1-first=Torsten|author1-last=Böker|chapter=Nuclear star clusters}} * {{cite book|title=The Impact of HST on European Astronomy|series=Astrophysics and Space Science Proceedings|editor1-first=F. Duccio|editor1-last=Macchetto|publisher=Springer Science & Business Media|year=2010b|isbn=9789048134007|author1-first=Torsten|author1-last=Böker|chapter=Young Massive Star Clusters in the Era of the Hubble Space Telescope}} {{refend}} {{Galaxy}}
Category:Concepts in astrophysics Category:Supermassive black holes Category:Star systems
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