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Formation of supermassive black holes in galactic nuclei – I. Delivering seed intermediate-mass black holes in massive stellar clusters

Askar, Abbas LU orcid ; Davies, Melvyn B. LU and Church, Ross P. LU orcid (2021) In Monthly Notices of the Royal Astronomical Society 502(2). p.2682-2700
Abstract
Supermassive black holes (SMBHs) are found in most galactic nuclei. A significant fraction of these nuclei also contains a nuclear stellar cluster (NSC) surrounding the SMBH. In this paper, we consider the idea that the NSC forms first, from the merger of several stellar clusters that may contain intermediate-mass black holes (IMBHs). These IMBHs can subsequently grow in the NSC and form an SMBH. We carry out N-body simulations of the simultaneous merger of three stellar clusters to form an NSC, and investigate the outcome of simulated runs containing zero, one, two, and three IMBHs. We find that IMBHs can efficiently sink to the centre of the merged cluster. If multiple merging clusters contain an IMBH, we find that an IMBH... (More)
Supermassive black holes (SMBHs) are found in most galactic nuclei. A significant fraction of these nuclei also contains a nuclear stellar cluster (NSC) surrounding the SMBH. In this paper, we consider the idea that the NSC forms first, from the merger of several stellar clusters that may contain intermediate-mass black holes (IMBHs). These IMBHs can subsequently grow in the NSC and form an SMBH. We carry out N-body simulations of the simultaneous merger of three stellar clusters to form an NSC, and investigate the outcome of simulated runs containing zero, one, two, and three IMBHs. We find that IMBHs can efficiently sink to the centre of the merged cluster. If multiple merging clusters contain an IMBH, we find that an IMBH binary is likely to form and subsequently merge by gravitational wave emission. We show that these mergers are catalyzed by dynamical interactions with surrounding stars, which systematically harden the binary and increase its orbital eccentricity. The seed SMBH will be ejected from the NSC by the recoil kick produced when two IMBHs merge, if their mass ratio q ≳ 0.15. If the seed is ejected then no SMBH will form in the NSC. This is a natural pathway to explain those galactic nuclei that contain an NSC but apparently lack an SMBH, such as M33. However, if an IMBH is retained then it can seed the growth of an SMBH through gas accretion and tidal disruption of stars. (Less)
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author
; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Gravitational waves, Methods: numerical, Quasars: supermassive black holes, Galaxies: star clusters: general
in
Monthly Notices of the Royal Astronomical Society
volume
502
issue
2
pages
19 pages
publisher
Oxford University Press
external identifiers
  • scopus:85104306828
ISSN
0035-8711
DOI
10.1093/mnras/stab113
language
English
LU publication?
yes
id
4bd54ccd-2b36-4d7a-b118-e607200c3b98
date added to LUP
2021-04-22 10:35:49
date last changed
2024-04-20 06:12:12
@article{4bd54ccd-2b36-4d7a-b118-e607200c3b98,
  abstract     = {{Supermassive black holes (SMBHs) are found in most galactic nuclei. A significant fraction of these nuclei also contains a nuclear stellar cluster (NSC) surrounding the SMBH. In this paper, we consider the idea that the NSC forms first, from the merger of several stellar clusters that may contain intermediate-mass black holes (IMBHs). These IMBHs can subsequently grow in the NSC and form an SMBH. We carry out <em>N</em>-body simulations of the simultaneous merger of three stellar clusters to form an NSC, and investigate the outcome of simulated runs containing zero, one, two, and three IMBHs. We find that IMBHs can efficiently sink to the centre of the merged cluster. If multiple merging clusters contain an IMBH, we find that an IMBH binary is likely to form and subsequently merge by gravitational wave emission. We show that these mergers are catalyzed by dynamical interactions with surrounding stars, which systematically harden the binary and increase its orbital eccentricity. The seed SMBH will be ejected from the NSC by the recoil kick produced when two IMBHs merge, if their mass ratio <em>q</em> ≳ 0.15. If the seed is ejected then no SMBH will form in the NSC. This is a natural pathway to explain those galactic nuclei that contain an NSC but apparently lack an SMBH, such as M33. However, if an IMBH is retained then it can seed the growth of an SMBH through gas accretion and tidal disruption of stars.}},
  author       = {{Askar, Abbas and Davies, Melvyn B. and Church, Ross P.}},
  issn         = {{0035-8711}},
  keywords     = {{Gravitational waves; Methods: numerical; Quasars: supermassive black holes; Galaxies: star clusters: general}},
  language     = {{eng}},
  month        = {{02}},
  number       = {{2}},
  pages        = {{2682--2700}},
  publisher    = {{Oxford University Press}},
  series       = {{Monthly Notices of the Royal Astronomical Society}},
  title        = {{Formation of supermassive black holes in galactic nuclei – I. Delivering seed intermediate-mass black holes in massive stellar clusters}},
  url          = {{http://dx.doi.org/10.1093/mnras/stab113}},
  doi          = {{10.1093/mnras/stab113}},
  volume       = {{502}},
  year         = {{2021}},
}