Electromagnetic extraction of energy from black hole-neutron star binaries

TL;DR

This paper proposes a new electromagnetic emission mechanism from black hole-neutron star binaries, driven by magnetic interactions, which could produce detectable signals coinciding with gravitational wave detections.

Contribution

It introduces a novel electromagnetic emission process involving Poynting flux and plasma radiation during black hole-neutron star mergers, expanding potential multi-messenger observations.

Findings

Electromagnetic luminosity comparable to supernovae and AGN.

Interaction of black hole magnetic fields with neutron star magnetosphere generates observable signals.

Potential for simultaneous gravitational wave and electromagnetic detection.

Abstract

The coalescence of black hole-neutron star binaries is expected to be a principal source of gravitational waves for the next generation of detectors, Advanced LIGO and Advanced Virgo. Ideally, these and other gravitational wave sources would have a distinct electromagnetic counterpart, as significantly more information could be gained through two separate channels. In addition, since these detectors will probe distances with non-negligible redshift, a coincident observation of an electromagnetic counterpart to a gravitational wave signal would facilitate a novel measurement of dark energy [1]. For black hole masses not much larger than the neutron star mass, the tidal disruption and subsequent accretion of the neutron star by the black hole provides one avenue for generating an electromagnetic counterpart [2]. However, in this work, we demonstrate that, for all black hole-neutron star binaries observable by Advanced LIGO/Virgo, the interaction of the black hole with the magnetic field of the neutron star will drive a Poynting flux. This Poynting flux generates synchrotron/curvature radiation as the electron-positron plasma in the neutron star magnetosphere is accel- erated, and thermal radiation as the plasma is focused onto the neutron star magnetic poles, creating a "hot spot" on the neutron star surface. This novel effect will gener- ate copious luminosity, comparable to supernovae and active galactic nuclei, so that black hole-neutron star coalescences detectable with gravitational waves by Advanced LIGO/Virgo could also potentially be detectable electromagnetically.