Massive Black Holes in Star Clusters. II. Realistic Cluster Models

By H. Baumgardt, J. Makino, Toshikazu Ebisuzaki. 2004

161 citations recorded by the source corpus.

We have followed the evolution of multimass star clusters containing massive central black holes through collisional N-body simulations done on GRAPE6. Each cluster is composed of between 16,384 and 131,072 stars together with a black hole with an initial mass of MBH = 1000 M☉. We follow the evolution of the clusters under the combined influence of two-body relaxation, stellar mass loss, and tidal disruption of stars by the massive central black hole. We find that the (three-dimensional) mass density profile follows a power-law distribution ρ ~ r-α with slope α = 1.55 inside the sphere of influence of the central black hole. This leads to a constant-density profile of bright stars in projection, which makes it highly unlikely that core-collapse clusters contain intermediate-mass black holes (IMBHs). Instead, globular clusters containing massive central black holes can be fitted with standard King profiles. Because of energy generation in the cusp, star clusters with IMBHs expand. The cluster expansion is so strong that clusters that start very concentrated can end up among the least dense clusters. The amount of mass segregation in the core is also smaller compared to postcollapse clusters without IMBHs. Most stellar mass black holes with masses MBH > 5 M☉ are lost from the clusters within a few gigayears through mutual encounters in the cusp around the IMBH. Black holes in star clusters disrupt mainly main-sequence stars and giants and no neutron stars. The disruption rates are too small to form an IMBH out of a MBH ≈ 50 M☉ progenitor black hole even if all material from disrupted stars is accreted onto the black hole, unless star clusters start with central densities significantly higher than what is seen in present-day globular clusters. We also discuss the possible detection mechanisms for IMBHs. Our simulations show that kinematical studies can reveal 1000 M☉ IMBHs in the closest clusters. IMBHs in globular clusters are weak X-ray sources, since the tidal disruption rate of stars is low and the star closest to the IMBH is normally another black hole, which prevents other stars from undergoing stable mass transfer. For globular clusters, dynamical evolution can push compact stars near the IMBH to distances small enough that they become detectable sources of gravitational radiation. If 10% of all globular clusters contain IMBHs, extragalactic globular clusters could be one of the major sources of gravitational wave events for LISA.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/7a358c8f11ed7183cde0f04a81f2ae06b2df63fb

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Citations in the corpus

Resonant Relaxation near a Massive Black Hole: The Stellar Distribution and Gravitational Wave Sources (2006, background): “The recent fully self-consistentN -body simulations of Baumgardt et al. (2004a, 2004b), Preto et al. ( 2004) and Merritt & Szell (2005), indicate that such studies are almost within reach of current hardware.”
The Effect of Mass Segregation on Gravitational Wave Sources near Massive Black Holes (2006, background): “The importance of mass-segregation on inspiral processes was dramatically demonstrated inN -body simulations (Baumgardt et al. 2004, 2005) of tidal capture of MS stars (Alexander & Morris 2003; Hopman et al. 2004).”
TIDAL DISRUPTION AND IGNITION OF WHITE DWARFS BY MODERATELY MASSIVE BLACK HOLES (2008, background): “…dwarfs by moderately massive black holes, with particular reference to the centers of dwarf galaxies (e.g. Mathur et al. 2008), globular clusters (e.g. Portegies Zwart et al. 2004; Baumgardt et al. 2004) and the intermediate-mass black hole candidates in active galactic nuclei (Greene & Ho 2004).”
Runaway collisions in young star clusters - II. Numerical results (2005, background): “…the central regions re-expand as a result of the heating effect of the accretion of deeply bound stars by the central object, as in a cluster with a central BH destroying or ejecting stars that come too close (Shapiro 1977; Duncan & Shapiro 1982; Amaro-Seoane et al. 2004; Baumgardt et al. 2004a,b).”
The life cycle of star clusters in a tidal field (2011, background): “…-body simulations of star clusters these binaries are usually considered to be primordial, but other mechanisms of energy generation have been modelled, including the actionof a central intermediate-mass black hole (Baumgardt et al. 2004) and, less controversially, mass-loss from stellar evolution.”
Stellar Remnants in Galactic Nuclei: Mass Segregation (2006, methodology): “In particular, we performed a new NBODY4 simulation of a two-component model with a central massive object using 64,000 particles.”
The Orbital Statistics of Stellar Inspiral and Relaxation near a Massive Black Hole: Characterizing Gravitational Wave Sources (2005, unknown): “The radial distribution of the different mass components can be then approximated as average power laws, steeper ( p > 0) for the heavier masses and flatter ( pP0) for the lower masses (Bahcall & Wolf 1977; Baumgardt et al. 2004b).”
STRONG MASS SEGREGATION AROUND A MASSIVE BLACK HOLE (2008, background): “In these theoretical models αL ≃1.5, while αH &2 at r ∼0.1 pc. N-body simulations of stellar clusters with evolving stellar populations and a central intermediate mass black hole (IMBH) also provide hints of strong mass segregation (Baumgardt et al. 2004, J. Makino, priv. comm.).”
Binary Mergers and Growth of Black Holes in Dense Star Clusters (2005, background): “Also, Kingmodels with lowerW0 are more likely to form candidate IMBHs.”
Masses and scaling relations for nuclear star clusters, and their co-existence with central black holes (2016, unknown): “These simulations also show that a significant fraction of stars can escape from the cluster due to close encounters with the MBH (Baumgardt et al. 2004a, 2006).”