# Collisionless losscone refilling: the end of the final parsec problem

Speaker | Talk Date | Talk Series |
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Alessia Gualandris (Surrey) | 10 October 2019 | Institute of Astronomy Colloquia |

#### Abstract

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.

#### Presentation

*Presentation unavailable*