Modeling Flows Around Merging Black Hole Binaries

TL;DR

This paper models the behavior of matter around merging black hole binaries in general relativity to identify potential electromagnetic signals associated with gravitational wave events.

Contribution

It presents the first 3D general relativistic simulations of pressureless matter flow around merging black holes, highlighting differences based on binary properties.

Findings

Differences in collision and outflow speeds between single and binary black holes.

Signatures of the merger in low angular momentum matter.

Potential electromagnetic counterparts to gravitational wave signals.

Abstract

Coalescing massive black hole binaries are produced by the mergers of galaxies. The final stages of the black hole coalescence produce strong gravitational radiation that can be detected by the space-borne LISA. In cases where the black hole merger takes place in the presence of gas and magnetic fields, various types of electromagnetic signals may also be produced. Modeling such electromagnetic counterparts of the final merger requires evolving the behavior of both gas and fields in the strong-field regions around the black holes. We have taken a step towards solving this problem by mapping the flow of pressureless matter in the dynamic, 3-D general relativistic spacetime around the merging black holes. We find qualitative differences in collision and outflow speeds, including a signature of the merger when the net angular momentum of the matter is low, between the results from single and binary black holes, and between nonrotating and rotating holes in binaries. If future magnetohydrodynamic results confirm these differences, it may allow assessment of the properties of the binaries as well as yielding an identifiable electromagnetic counterpart to the attendant gravitational wave signal.