Multimessenger signals from black hole-neutron star mergers without significant tidal disruption

TL;DR

This study uses advanced simulations to explore electromagnetic signals from black hole-neutron star mergers with minimal tidal disruption, revealing potential for observable electromagnetic emissions and jet formation under certain conditions.

Contribution

It demonstrates that significant electromagnetic radiation can occur even with little neutron star matter remaining, highlighting the role of magnetosphere interactions in such mergers.

Findings

Electromagnetic radiation is powered by magnetosphere interactions.

Strong magnetic field twisting leads to plasmoid emission before merger.

Post-merger, magnetic fields can form jets in more favorable scenarios.

Abstract

We study the multimessenger signals from the merger of a black hole with a magnetized neutron star using resistive magnetohydrodynamics simulations coupled to full general relativity. We focus on a case with a 5:1 mass ratio, where only a small amount of the neutron star matter remains post-merger, but we nevertheless find that significant electromagnetic radiation can be powered by the interaction of the neutron star's magnetosphere with the black hole. In the lead-up to merger, strong twisting of magnetic field lines from the inspiral leads to plasmoid emission and results in a luminosity in excess of that expected from unipolar induction. We find that the strongest emission occurs shortly after merger during a transitory period in which magnetic loops form and escape the central region. The remaining magnetic field collimates around the spin axis of the remnant black hole before dissipating, an indication that, in more favorable scenarios (higher black hole spin/lower mass ratio) with larger accretion disks, a jet would form.