Electromagnetic signatures of merging Black holes.

Maxim Lyutikov

February 07, 2011

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Abstract: Understanding the electromagnetic signatures of merging black holes is most desirable, as this will provide crucial information on the location and the physical properties of the event. We identify two types of electromagnetic jets of similar power produces by merging BHs moving in a magnetic field supported by an external accretion disk: (i) due to rotation of space-time within the orbit; (ii) due to unipolar induction mechanism. In the latter case, the magnetospheres of black holes resemble in many respects the magnetospheres of rotationally-powered pulsars, with induced charge density, pair formation fronts and outer gaps, where the sign of the induced charge changes. As a result, a black hole moving linearly through magnetic field will generate bipolar electromagnetic jets each consisting of two counter-aligned current flows (four current flows total). The resulting Poynting power is $ L approx {(G M)3 B_02 /( c5 R) }$, where $R$ is the radius of the orbit. Since the resulting electrodynamics is in many respects similar to pulsars, merging black holes may generate coherent radio and high energy emission beamed approximately along the orbital normal. In addition, merging BHs may produce observable wind-driven cavities.