Black holes in galaxies: environmental impact on gravitational-wave generation and propagation

TL;DR

This paper introduces new black hole solutions in Einstein's gravity that incorporate galactic environments, enabling better understanding of how surroundings influence gravitational-wave signals and black hole observations.

Contribution

The work presents a family of asymptotically flat black hole solutions with 'hair' that model galactic environments, extending Einstein clusters to include horizons for astrophysical applications.

Findings

External matter causes gravitational redshift corrections to ringdown signals.

Galactic potential influences gravitational-wave propagation in measurable ways.

Solutions can help constrain galactic environments using electromagnetic and gravitational-wave data.

Abstract

We introduce a family of solutions of Einstein's gravity minimally coupled to an anisotropic fluid, describing asymptotically flat black holes with "hair" and a regular horizon. These spacetimes can describe the geometry of galaxies harboring supermassive black holes, and are extensions of Einstein clusters to include horizons. They are useful to constrain the environment surrounding astrophysical black holes, using electromagnetic or gravitational-wave observations. We compute the main properties of the geometry, including the corrections to the ringdown stage induced by the external matter and fluxes by orbiting particles. The leading order effect to these corrections is a gravitational-redshift, but gravitational-wave propagation is affected by the galactic potential in a nontrivial way, and may be characterized with future observatories.