Simulations of Recoiling Massive Black Holes in the via Lactea Halo

Abstract

The coalescence of a massive black hole (MBH) binary leads to the gravitational-wave recoil of the system and its ejection from the galaxy core. We have carried out N-body simulations of the motion of a M BH = 3.7 × 10 6 M MBH remnant in the "Via Lactea I" simulation, a Milky Way-sized dark matter halo. The black hole receives a recoil velocity of V kick = 80, 120, 200, 300, and 400 km s −1 at redshift 1.5, and its orbit is followed for over 1 Gyr within a "live" host halo, subject only to gravity and dynamical friction against the dark matter background. We show that, owing to asphericities in the dark matter potential, the orbit of the MBH is highly nonradial, resulting in a significantly increased decay timescale compared to a spherical halo. The simulations are used to construct a semi-analytic model of the motion of the MBH in a time-varying triaxial Navarro-Frenk-White dark matter halo plus a spherical stellar bulge, where the dynamical friction force is calculated directly from the velocity dispersion tensor. Such a model should offer a realistic picture of the dynamics of kicked MBHs in situations where gas drag, friction by disk stars, and the flattening of the central cusp by the returning black hole are all negligible effects. We find that MBHs ejected with initial recoil velocities V kick 500 km s −1 do not return to the host center within a Hubble time. In a Milky Way-sized galaxy, a recoiling hole carrying a gaseous disk of initial mass ∼ M BH may shine as a quasar for a substantial fraction of its "wandering" phase. The long decay timescales of kicked MBHs predicted by this study may thus be favorable to the detection of off-nuclear quasar activity.

Interaction of Recoiling Supermassive Black Holes With Stars in Galactic Nuclei

“…That keeps the trajectory of the SMBH inside the bulge, where the impact of the dark matter halo is very weak compared with baryonic matter. For this reason, we neglect the influence of the triaxial dark matter halo, which is mentioned by Guedes et al (2009).…”

Numerical simulations of black-hole binaries and gravitational wave emission

“…Typical escape veloc-ities range from ∼ 10 km/s for dwarf galaxies up to ∼ 1000 km/s for giant elliptic galaxies [259]. Large kicks would displace or eject the merged hole from its host, with possibly observable consequences: a softening of the stellar density gradient in the galactic nucleus, off-center radio-loud active galactic nuclei, off-nuclear X-ray sources in nearby galaxies and the generation of electromagnetic signals via interaction of the BH with its gaseous environment [260,261,262,259,263,264,265,266,267,268,269]. BH ejection represents a potential obstacle for BH growth via merger, and thus puts constraints on merger-history models, which must be able to explain the assembly of SMBHs by redshifts z 6 [261,270,271].…”

Prompt electromagnetic transients from binary black hole mergers

“…A number of mechanisms may provide signals associated with these sources across a broad range of time scales from ∼10 9 years before merger to ∼10 9 years after merger [13]. Considerable evidence for binary SMBH systems has already been observed, but is restricted to those either well before merger [14][15][16][17][18][19][20][21], or well after merger [22][23][24][25][26][27][28].…”