University of Cambridge > > Institute of Astronomy Colloquia > Collisionless losscone refilling: the end of the final parsec problem

Collisionless losscone refilling: the end of the final parsec problem

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Mergers of massive black hole binaries (BHBs) are expected to be a key source of gravitational waves (GWs). However, the expected number and frequency of such mergers remains highly uncertain. This owes to a long-standing puzzle known as the final parsec problem. Gravitational N-body simulations that assume a spherical distribution of stars surrounding the BHB find that the binary stalls when all stars on intersecting orbits have been ejected. This is inconsistent with available observations: every massive galaxy observed to date appears to host a single supermassive black hole, and only a handful of BHB candidates exist.   I will review the final parsec problem and present a new approach to determine whether collisionless repopulation of the binary’s losscone in non-spherical nuclei is a viable mechanism to drive binary coalescence. I will present results of direct summation N-body simulations of galaxy mergers, running on multiple GPUs. These allow to measure the binary hardening rate and determine a new proxy that depends only on the stars’ angular momentum. I will then present collisionless simulations of spherical and non-spherical isolated models to increase the number of particles sufficiently that collisional effects become unimportant and collisionless losscone refilling can be measured.

This talk is part of the Institute of Astronomy Colloquia series.

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