Hardening in a stellar time-evolving background: Prospects for LISA

Abstract

We use detailed scattering experiments to study the role of 3-body interactions in driving orbital decay of massive black hole binaries (MBHBs) in galactic centers, quantifying also the effect of secondary slingshot on binary shrinking. We find that without invoking other physical mechanisms, such as gas dynamical processes, binaries cannot shrink to the gravitational wave (GW) emission regime in less than a Hubble time, unless they have very small mass ratios. Very unequal mass binaries are therefore a natural target for the planned Laser Interferometer Space Antenna (LISA). The star-binary interactions create a population of hypervelocity stars on nearly radial corotating orbits that is highly flattened in the inspiral plane. Most of the stars are ejected in an initial burst lasting much less then the bulge crossing time. © 2008 Springer-Verlag Berlin Heidelberg.