Estimating the Prompt Electromagnetic Luminosity of a Black Hole Merger

TL;DR

This paper predicts the electromagnetic luminosity from black hole mergers, showing it can reach the Eddington luminosity and last longer than the merger itself, depending on gas properties.

Contribution

It introduces a model linking gas heating and optical thickness to the electromagnetic luminosity during black hole mergers, highlighting the potential for observable signals.

Findings

Electromagnetic luminosity can reach the Eddington limit.

The photon signal duration scales with gas mass.

Additional dissipation mechanisms can extend the emission timescale.

Abstract

Although recent work in numerical relativity has made tremendous strides in quantifying the gravitational wave luminosity of black hole mergers, very little is known about the electromagnetic luminosity that might occur in immediate conjunction with these events. We show that whenever the heat deposited in the gas near a pair of merging black holes is proportional to its total mass, and the surface density of the gas in the immediate vicinity is greater than the (quite small) amount necessary to make it optically thick, the characteristic scale of the luminosity emitted in direct association with the merger is the Eddington luminosity independent of the gas mass. The duration of the photon signal is proportional to the gas mass, and is generally rather longer than the merger event. At somewhat larger distances, dissipation associated with realigning the gas orbits to the new spin orientation of the black hole can supplement dissipation of the energy gained from orbital adjustment to the mass lost in gravitational radiation; these two heat sources can combine to augment the electromagnetic radiation over longer timescales.