Perturbed disks get shocked. Binary black hole merger effects on accretion disks

TL;DR

This study investigates how binary black hole mergers affect surrounding accretion disks, revealing that recoil velocities can induce shocks and modulate luminosity, offering potential electromagnetic signatures to measure black hole kicks.

Contribution

The paper presents the first detailed analysis of how black hole recoil impacts accretion disk dynamics and observable radiation, highlighting shock formation and energy modulation effects.

Findings

Recoil can induce relativistic shocks in accretion disks.

Luminosity variations correlate with recoil velocity.

Characteristic energy patterns can reveal black hole kick velocities.

Abstract

The merger process of a binary black hole system can have a strong impact on a circumbinary disk. In the present work we study the effect of both central mass reduction (due to the energy loss through gravitational waves) and a possible black hole recoil (due to asymmetric emission of gravitational radiation). For the mass reduction case and recoil directed along the disk's angular momentum, oscillations are induced in the disk which then modulate the internal energy and bremsstrahlung luminosities. On the other hand, when the recoil direction has a component orthogonal to the disk's angular momentum, the disk's dynamics are strongly impacted, giving rise to relativistic shocks. The shock heating leaves its signature in our proxies for radiation, the total internal energy and bremsstrahlung luminosity. Interestingly, for cases where the kick velocity is below the smallest orbital velocity in the disk (a likely scenario in real AGN), we observe a common, characteristic pattern in the internal energy of the disk. Variations in kick velocity simply provide a phase offset in the characteristic pattern implying that observations of such a signature could yield a measure of the kick velocity through electromagnetic signals alone.