Matter flows around black holes and gravitational radiation

TL;DR

This paper introduces a new method to estimate gravitational radiation from matter near black holes, using numerical simulations of relativistic hydrodynamics and curvature perturbations, focusing on non-rotating black holes and axisymmetric flows.

Contribution

The authors develop and calibrate a novel approach for calculating gravitational waves from complex matter motions around black holes, including a new initial data prescription and analysis of various matter infall scenarios.

Findings

Black hole quasi-normal modes can be excited by matter shells.

Gravitational wave energy depends on shell parameters like thickness and velocity.

The method effectively models gravitational radiation from axisymmetric matter flows.

Abstract

We develop and calibrate a new method for estimating the gravitational radiation emitted by complex motions of matter sources in the vicinity of black holes. We compute numerically the linearized curvature perturbations induced by matter fields evolving in fixed black hole backgrounds, whose evolution we obtain using the equations of relativistic hydrodynamics. The current implementation of the proposal concerns non-rotating holes and axisymmetric hydrodynamical motions. As first applications we study i) dust shells falling onto the black hole isotropically from finite distance, ii) initially spherical layers of material falling onto a moving black hole, and iii) anisotropic collapse of shells. We focus on the dependence of the total gravitational wave energy emission on the flow parameters, in particular shell thickness, velocity and degree of anisotropy. The gradual excitation of the black hole quasi-normal mode frequency by sufficiently compact shells is demonstrated and discussed. A new prescription for generating physically reasonable initial data is discussed, along with a range of technical issues relevant to numerical relativity.