Simulating black hole binaries by imposing conservation laws

Yohai Meiron

September 26, 2011

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Abstract: We present a new approach to studying the evolution of massive black hole binaries in a stellar environment. By imposing conservation of total energy and angular momentum, we find the forces that are exerted on the black holes by the stars, and thus obtain the decaying path of the black hole binary from the dynamical friction regime down to subparsec scales. Our scheme lies between scattering experiments and N-body simulations, and enjoys some advantages of both. While still resolving collisions between stars and black holes, the it is fast enough so it was possible to use a large number of particles. We studied both an equal mass and 1:10 mass ratio binaries under various initial conditions. Our results are BH tracks that are independent of the number of particles and are scalable with mass. We show that while an equal mass binary stalls at a nearly circular orbit, a runaway growth of eccentricity occurs for the 1:10 mass ratio case. This effect reduces the timescale for black hole coalescence through gravitational radiation to well below the Hubble time, even in a spherical and gasless system formed by dry mergers.