Bondi-Hoyle-Lyttleton accretion onto a rotating black hole with ultralight scalar hair

TL;DR

This paper numerically investigates how ultralight scalar hair affects relativistic accretion onto black holes, revealing unique shock structures and oscillations that could relate to observed astrophysical phenomena.

Contribution

It introduces the first detailed numerical analysis of Bondi-Hoyle-Lyttleton accretion onto hairy black holes with ultralight scalar fields, highlighting new shock behaviors and oscillation frequencies.

Findings

Steady-state accretion solutions with shock cones and stagnation points.

Shock cone envelops the black hole in models with large scalar field component.

Identified quasi-periodic oscillations potentially linked to astrophysical observations.

Abstract

We present a numerical study of relativistic Bondi-Hoyle-Lyttleton (BHL) accretion onto an asymptotically flat black hole with synchronized hair. The hair is sourced by an ultralight, complex scalar field, minimally coupled to Einstein's gravity. Our simulations consider a supersonic flow parametrized by the asymptotic values of the fluid quantities and a sample of hairy black holes with different masses, angular momenta, and amount of scalar hair. For all models, steady-state BHL accretion solutions are attained that are characterized by the presence of a shock-cone and a stagnation point downstream. For the models of the sample with the largest component of scalar field, the shock-cone envelops fully the black hole, transitioning into a bow-shock, and the stagnation points move further away downstream. Analytical expressions for the mass accretion rates are obtained after fitting the numerical results, which can be used to analyze black-hole formation scenarios in the presence of ultralight scalar fields. The formation of a shock-cone leads to regions where sound waves can be trapped and resonant oscillations excited. We measure the frequencies of such quasi-periodic oscillations and point out a possible association with quasi-periodic oscillations in the X-ray light curve of Sgr~A* and microquasars.