Formation of Galactic Nuclei

By Milos Milosavljevic, D. Merritt. 2001

513 citations recorded by the source corpus.

We investigate a model in which galactic nuclei form via the coalescence of preexisting stellar systems containing supermassive black holes. Merger simulations are carried out using N-body algorithms that can follow the formation and decay of a black hole binary and its effect on the surrounding stars down to subparsec scales. Our initial stellar systems have steep central density cusps similar to those in low-luminosity elliptical galaxies. Immediately following the merger, the density profile of the remnant is homologous with the initial density profile and the steep nuclear cusp is preserved. However, the formation of a black hole binary transfers energy to the stars and lowers the central density; continued decay of the binary creates a ρ ~ r-1 density cusp similar to those observed in bright elliptical galaxies, with a break radius that extends well beyond the sphere of gravitational influence of the black holes. Our simulations are the first to successfully produce shallow power-law cusps from mergers of galaxies with steep cusps, and our results support a picture in which the observed dependence of nuclear cusp slope on galaxy luminosity is a consequence of galaxy interactions. We follow the decay of the black hole binary over a factor of ~20 in separation after formation of a hard binary, considerably farther than in previous simulations. We see almost no dependence of the binary's decay rate on number of particles in the simulation, contrary to earlier studies in which a lower initial density of stars led to a more rapid depletion of the binary's loss cone. We nevertheless argue that the decay of a black hole binary in a real galaxy would be expected to stall at separations of 0.01-1 pc unless some additional mechanism is able to extract energy from the binary. We discuss the implications of our results for the survivability of dark matter cusps.

Subfields: Astronomy and Astrophysics, Instrumentation, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/4be41b06da3fe9d53e08bbbc957f35dcb6b48514

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Citations in the corpus

Structure and Kinematics of Early-Type Galaxies from Integral Field Spectroscopy (2016, background): “…mergers leave an imprint in the nuclear profiles, when supermassive black holes of the merging galaxies sink towards the center via dynamical friction and eject stars in radial orbits, scouring a nuclear core or deficit (e.g. Faber et al. 1997; Milosavljević & Merritt 2001; Kormendy & Ho 2013).”
A New Empirical Model for the Structural Analysis of Early-Type Galaxies, and A Critical Review of the Nuker Model (2003, background): “…of a galaxy may have been partially evacuated by the coalescence of merging supermassive black holes (SMBHs; e.g., Ebisuzaki, Makino, & Okumura 1991; Makino & Ebisuzaki 1996; Faber et al. 1997; Makino 1997; Quillen, Bower, & Stritzinger 2000; Alexander & Livio 2001; Milosavljević & Merritt 2001).”
Gravitational N-Body Simulations (2003, methodology): “A direct solution method is described [Milosavljević & Merritt, 2001].”
The Kinematic Structure of Merger Remnants (2006, background): “Unfortunately, with this resolution we cannot reliably determine the inner (≤ 140 pc) surface density profiles (Lauer et al. 2005, and references therein) nor follow the merger of the binary black holes (see, e.g., Milosavljević & Merritt 2001).”
Supermassive black hole binaries in gaseous and stellar circumnuclear discs: orbital dynamics and gas accretion (2006, background): “For example, three–body encounters with background stars may become important at MBHs separations ∼ < rinf ≈ 6 pc (Quinlan 1996; Milosavljevic & Merritt 2001; Merritt 2006).”
Accretion during the Merger of Supermassive Black Holes (2002, background): “The extent of this loss cone depletion remains a subject of active debate (Milosavljevic & Merritt 2001; Yu 2002; Zhao, Haehnelt & Rees 2002), with recent work suggesting that stellar dynamical processes may suffice to bring binaries into the gravitational radiation dominated regime.”
Axisymmetric Dynamical Models of the Central Regions of Galaxies (2002, background): “Fortunately, the large number of researchers working in this area now (e.g., Milosavljevic & Merritt 2001; HolleyBockelmann et al. 2002) will provide improved theoretical comparisons.”
Nuclear star clusters (2009, background): “This process likely leads to the formation of binary black holes which, in the process of coalescence, transfer energy to the surrounding stars, thus decreasing the central density and effectively destroying the NSC (e.g., Quinlan and Hernquist 1997; Milosavljević and Merritt 2001).”
THE BLACK HOLE MASS IN M87 FROM GEMINI/NIFS ADAPTIVE OPTICS OBSERVATIONS (2011, background): “Additionally, binary black holes will result in a significantly increase tangential anisotropy (Milosavljevic & Merritt 2001), similar to the amount seen here in M87.”
Massive Black Hole Binary Evolution (2004, methodology): “he stellar density around the binary drops very quickly after the binary reaches a separation a ≈ ah. Figure 8: Lagrangian radii around each of the two SBH particles in an equalmass merger simulation [147]. ¿From bottom to top, the radii enclose 10−4, 10−3.5 , 10−3, 10−2.5, 10−2 −1.5 and 10−1 in uni”
AN EXTREMELY TOP-HEAVY INITIAL MASS FUNCTION IN THE GALACTIC CENTER STELLAR DISKS (2009, background): “The in-spiral of an intermediate mass black hole can plausibly gouge out a large enough core in the stellar distribution (Milosavljevic & Merritt 2001; Baumgardt et al. 2006) but there is no evidence for such a second black hole from the dynamical properties of the S-stars or late type stars, nor…”
Growth and activity of black holes in galaxy mergers with varying mass ratios (2014, background): “However, the time-scales for BH merging are still very uncertain and could be even longer than 1 Gyr (the ‘final parsec problem’; see, e.g., Begelman, Blandford & Rees 1980; Milosavljević & Merritt 2001).”
INSPIRALLING SUPERMASSIVE BLACK HOLES: A NEW SIGNPOST FOR GALAXY MERGERS (2008, background): “The two SMBHs will remain at separations & 1 kpc for ∼ 100 Myr, then form a SMBH binary of parsec-scale separation (Milosavljević & Merritt 2001; Begelman et al. 1980).”
The Kozai Mechanism and the Evolution of Binary Supermassive Black Holes (2002, methodology): “However, numerical simulations of black hole binary evolution by Milosavljević & Merritt (2001) suggest that this is rather unlikely.”
STRUCTURE AND FORMATION OF ELLIPTICAL AND SPHEROIDAL GALAXIES (2008, methodology): “…of mass deficits depended on the functional form used to extrapolate the outer profile inward to the center; they are larger for Nuker function extrapolations (Milosavljević & Merritt 2001; Milosavljevíc et al. 2002; Ravindranath et al. 2002) and smaller for Sérsic function extrapolations.”
Stellar Dynamics and Stellar Phenomena Near a Massive Black Hole (2017, background): “…cusp can be destroyed, or prevented from forming by external perturbations, such as galactic mergers that lead to the formation of a MBH binary, which slings out the stars inside its orbit as it decays (Begelman, Blandford & Rees 1980; Milosavljević & Merritt 2001; Merritt & Milosavljević 2005).”