Astrophysical signatures of boson stars: quasinormal modes and inspiral resonances

TL;DR

This paper investigates the gravitational-wave signatures of boson stars, revealing distinctive resonant-mode excitations that could differentiate them from black holes in astrophysical observations.

Contribution

It provides the first fully relativistic analysis of boson star configurations, their quasinormal modes, and their gravitational-wave responses to inspiraling objects.

Findings

Boson stars exhibit unique resonant-mode excitations during inspiral.

They can be distinguished from black holes through gravitational-wave signatures.

The study constructs several relativistic boson star models and analyzes their geodesic and oscillation spectra.

Abstract

Compact bosonic field configurations, or boson stars, are promising dark matter candidates which have been invoked as an alternative description for the supermassive compact objects in active galactic nuclei. Boson stars can be comparable in size and mass to supermassive black holes and they are hard to distinguish by electromagnetic observations. However, boson stars do not possess an event horizon and their global spacetime structure is different from that of a black hole. This leaves a characteristic imprint in the gravitational-wave emission, which can be used as a discriminant between black holes and other horizonless compact objects. Here we perform a detailed study of boson stars and their gravitational-wave signatures in a fully relativistic setting, a study which was lacking in the existing literature in many respects. We construct several fully relativistic boson star configurations, and we analyze their geodesic structure and free oscillation spectra, or quasinormal modes. We explore the gravitational and scalar response of boson star spacetimes to an inspiralling stellar-mass object and compare it to its black hole counterpart. We find that a generic signature of compact boson stars is the resonant-mode excitation by a small compact object on stable quasi-circular geodesic motion.