Extreme mass-ratio inspiral within an ultralight scalar cloud I. Scalar radiation

TL;DR

This paper investigates how an extreme mass-ratio inspiral (EMRI) within a scalar cloud around a black hole emits scalar radiation and how this affects gravitational-wave signals, revealing potential observable effects.

Contribution

It introduces a model for EMRI dynamics within a scalar cloud, quantifies scalar flux and phase shifts, and explores environmental effects on gravitational waves.

Findings

Scalar radiation is emitted towards infinity and the horizon.

Backreaction causes measurable gravitational-wave phase shifts.

Environmental effects depend on system parameters.

Abstract

In this work, we study the dynamics of an extreme mass-ratio inspiral (EMRI) embedded within a scalar cloud populated around the massive black hole. This cloud may be generated through the black hole superradiant process if the wavelength of the scalar particle is comparable to the size of the massive black hole. The EMRI motion perturbs the cloud, producing scalar radiation towards infinity and into the black hole horizon. In addition, the backreaction of the scalar radiation onto the orbit modifies the motion of the EMRI and induces an observable gravitational-wave phase shift for a range of system parameters. We quantify the scalar flux and the induced phase shift, as one of the examples of exactly-solvable, environmental effects of EMRIs.