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Abstract

This is a third installment in a program to develop a method for alleviating
the scale disparity in binary black hole simulations with mass ratios in the
intermediate astrophysical range, where simulation cost is prohibitive while
purely perturbative methods may not be adequate. The method is based on
excising a "worldtube" around the smaller object, much larger than the object
itself, replacing it with an analytical model that approximates a tidally
deformed black hole. Previously (arXiv:2304.05329) we have tested the idea in a
toy model of a scalar charge in a fixed circular geodesic orbit around a
Schwarzschild black hole, solving for the massless Klein-Gordon field in 3+1
dimensions on the SpECTRE platform. Here we take the significant further step
of allowing the orbit to evolve radiatively, in a self-consistent manner, under
the effect of back-reaction from the scalar field. We compute the inspiral
orbit and the emitted scalar-field waveform, showing a good agreement with
perturbative calculations in the adiabatic approximation. We also demonstrate
how our simulations accurately resolve post-adiabatic effects (for which we do
not have perturbative results). In this work we focus on quasi-circular
inspirals. Our implementation will shortly be publicly accessible in the
SpECTRE numerical relativity code.