# Enhanced tidal disruption rates from massive black hole binaries

## Xian Chen(1,2), Piero Madau(2), Alberto Sesana(3), & F. K. Liu(1,4)

(1) Department of Astronomy, Peking University, 100871 Beijing, China.

(2) Department of Astronomy & Astrophysics, University of California, Santa Cruz, CA 95064.

(3) Center for Gravitational Wave Physics, The Pennsylvania State University, University Park, State College, PA 16802.

(4) Kavli Institute for Astronomy and Astrophysics, Peking University, 100871 Beijing, China.

### Paper: ApJ, 2009, 697, L149

**Abstract:**
``Hard" massive black hole (MBH) binaries embedded in steep stellar cusps can shrink
via three-body slingshot interactions. We show that this process will inevitably be accompanied
by a burst of stellar tidal disruptions, at a rate that can be several orders of magnitude larger
than that appropriate for a single MBH. Our numerical scattering experiments reveal that: 1)
a significant fraction of stars initially bound to the primary hole are scattered into its tidal
disruption loss cone by gravitational interactions with the secondary hole, an enhancement effect
that is more pronounced for very unequal-mass binaries; 2) about 25% (40%) of all strongly
interacting stars are tidally disrupted by a MBH binary of mass ratio q=1/81 (q=1/243)
and eccentricity 0.1; and 3) two mechanisms dominate the fueling of the tidal
disruption loss cone, a Kozai non-resonant interaction that causes the secular evolution of the stellar
angular momentum in the field of the binary, and the effect of close encounters with the secondary
hole that change the stellar orbital parameters in a chaotic way. For a hard MBH binary of
10^{7} \msun and mass ratio 10^{-2}, embedded in an isothermal stellar cusp of velocity dispersion
sigma _*=100 km/sec , the tidal disruption rate can be as large as \dot N_* 1 yr^{-1}.
This is 4 orders of magnitude higher than estimated for a single MBH fed by two-body relaxation.
When applied to the case of a putative intermediate-mass black hole inspiraling onto
Sgr A^*, our results predict tidal disruption rates \dot N_* 0.05-0.1 yr^{-1}.

Preprints available from the authors at xchen3@ucsc.edu
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