Piercing of a boson star by a black hole

TL;DR

This study investigates the relativistic interaction between a black hole and a boson star, revealing significant accretion, tidal capture, and the formation of a gravitational atom, with implications for dark matter and gravitational wave emission.

Contribution

It provides the first detailed relativistic simulations of black hole piercing through boson stars, highlighting extreme accretion and tidal capture phenomena.

Findings

Black hole accretes over 95% of the boson star material.

Tidal capture binds the black hole and boson star, forming a gravitational atom.

Significant gravitational wave emission observed during interaction.

Abstract

New light fundamental fields are natural candidates for all or a fraction of dark matter. Self-gravitating structures of such fields might be common objects in the universe, and could comprise even galactic halos. These structures would interact gravitationally with black holes, a process of the utmost importance since it dictates their lifetime, the black hole motion, and possible gravitational radiation emission. Here, we study the dynamics of a black hole piercing through a much larger fully relativistic boson star, made of a complex minimally coupled massive scalar without self-interactions. As the black hole pierces through the bosonic structure, it is slowed down by accretion and dynamical friction, giving rise to gravitational-wave emission. Since we are interested in studying the interaction with large and heavy scalar structures, we consider mass ratios up to $q\sim 10$ and length ratios ${\cal L} \sim 62$. Somewhat surprisingly, for all our simulations, the black hole accretes more than 95% of the boson star material, even if an initially small black hole collides with large velocity. This is a consequence of an extreme "tidal capture" process, which binds the black hole and the boson star together, for these mass ratios. We find evidence of a "gravitational atom" left behind as a product of the process.