Prompt Tidal Disruption of Stars as an Electromagnetic Signature of Supermassive Black Hole Coalescence

TL;DR

This paper proposes that electromagnetic flares from tidally disrupted stars can serve as observable signatures of supermassive black hole mergers, aiding in identifying and studying these events alongside gravitational wave detections.

Contribution

It introduces a novel electromagnetic signature—stellar tidal disruptions—that indicates recent supermassive black hole coalescence, linking electromagnetic observations with gravitational wave sources.

Findings

Multiple electromagnetic flares can occur years after black hole mergers.

Disruption rates can reach approximately 0.1 per year post-merger.

Sequential disruptions can calibrate GW source rates for future detectors.

Abstract

A precise electromagnetic measurement of the sky coordinates and redshift of a coalescing black hole binary holds the key for using its gravitational wave (GW) signal to constrain cosmological parameters and to test general relativity. Here we show that the merger of ~10^{6-7}M_sun black holes is generically followed over a period of years by multiple electromagnetic flares from tidally disrupted stars. The sudden recoil imparted to the merged black hole by GW emission promptly fills its loss cone and results in a tidal disruption rate of stars as high as ~0.1 per year. The prompt disruption of a star within a single galaxy over a short period provides a unique electromagnetic flag of a recent black hole coalescence event, and sequential disruptions could be used on their own to calibrate the expected rate of GW sources for pulsar timing arrays or the proposed Laser Interferometer Space Antenna (LISA).