Ejection of Supermassive Black Holes from Galaxy Cores

By Alessia Gualandris, D. Merritt. 2007

196 citations recorded by the source corpus.

Recent numerical relativity simulations have shown that the emission of gravitational waves during the merger of two supermassive black holes (SMBHs) delivers a kick to the final hole, with a magnitude as large as 4000 km s−1. We study the motion of SMBHs ejected from galaxy cores by such kicks and the effects on the stellar distribution using high-accuracy direct N-body simulations. Following the kick, the motion of the SMBH exhibits three distinct phases. (1) The SMBH oscillates with decreasing amplitude, losing energy via dynamical friction at each core passage. Chandrasekhar's theory accurately reproduces the motion of the SMBH if 2≲ ln Λ ≲ 3 and if the changing core density is taken into account. (2) When the amplitude of the motion has fallen to roughly the core radius, the SMBH and core begin to exhibit oscillations about their common center of mass. These oscillations decay with a time constant that is at least 10 times longer than predicted by Chandrasekhar's formula. (3) Eventually, the SMBH reaches thermal equilibrium with the stars. The time for the SMBH's oscillations to damp to the Brownian level is as long as ~1 Gyr in the brightest galaxies. The longevity of the oscillations makes this mechanism competitive with others proposed to explain double or offset nuclei. Ejection of SMBHs also results in a lowered density of stars near the galaxy center; mass deficits as large as five times the SMBH mass can be produced. We compare the N-body density profiles with luminosity profiles of early-type galaxies in Virgo and show that even the largest observed cores can be reproduced by the kicks. Implications for displaced AGNs and helical radio structures are discussed.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/7385c72221a46782e04ff22c5ae2c28e028161b4

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Citations in the corpus

A LARGE SYSTEMATIC SEARCH FOR CLOSE SUPERMASSIVE BINARY AND RAPIDLY RECOILING BLACK HOLES (2011, unknown): “Otherwise, kicks can disturb the morphology of the host galaxy or offset an active nucleus from the center of its host (e.g., Gualandris & Merritt 2008; Komossa & Merritt 2008; Blecha et al. 2007).”
Quantifying the coexistence of massive black holes and dense nuclear star clusters (2009, background): “Once dry merging commences at MB ≈ −20.5 mag (e.g. Graham & Guzmán 2003, and references therein), or roughly MK ≈ −24 mag (or 5 × 10 10 to 10 11 M⊙), the MBH/M sph mass ratio should remain constant (or decrease if BHs can be ejected, e.g., Merritt et al. 2004; Gualandris & Merritt 2008).”
Doing Science with eLISA: Astrophysics and Cosmology in the Millihertz Regime (2012, background): “The kicked black hole, may return after a few oscillations down to the nuclear regions of the host galaxy, or escape the galaxy depending on the magnitude of the kick (Blecha et al., 2011, Blecha and Loeb, 2008, Gualandris and Merritt, 2008, Guedes et al., 2011).”
STRUCTURE AND FORMATION OF ELLIPTICAL AND SPHEROIDAL GALAXIES (2008, methodology): “Second, an additional process has been proposed to make large-Mdef/M• cores (Merritt et al. 2004; Boylan-Kolchin, Ma, & Quataert 2004; Gualandris & Merritt 2008).”