Extreme black hole simulations: collisions of unequal mass black holes and the point particle limit

TL;DR

This paper demonstrates that numerical relativity can accurately simulate collisions of unequal mass black holes up to a 1:100 mass ratio, effectively bridging non-linear and linearized gravitational physics.

Contribution

It extends the capability of numerical relativity to simulate extreme mass ratio black hole collisions and confirms the agreement with point-particle approximations.

Findings

Numerical simulations match linearized predictions for point-like particle infall.

Successfully simulate black hole collisions with mass ratios up to 1:100.

Identify and discuss the impact of initial data radiation.

Abstract

Numerical relativity has seen incredible progress in the last years, and is being applied with success to a variety of physical phenomena, from gravitational-wave research and relativistic astrophysics to cosmology and high-energy physics. Here we probe the limits of current numerical setups, by studying collisions of unequal mass, non-rotating black holes of mass-ratios up to 1:100 and making contact with a classical calculation in General Relativity: the infall of a point-like particle into a massive black hole. Our results agree well with the predictions coming from linearized calculations of the infall of point-like particles into non-rotating black holes. In particular, in the limit that one hole is much smaller than the other, and the infall starts from an infinite initial separation, we recover the point-particle limit. Thus, numerical relativity is able to bridge the gap between fully non-linear dynamics and linearized approximations, which may have important applications. Finally, we also comment on the "spurious" radiation content in the initial data and the linearized predictions.