Equatorial extreme-mass-ratio inspirals in Kerr black holes with scalar hair spacetimes

TL;DR

This paper investigates gravitational wave signals from extreme mass ratio inspirals around Kerr black holes with scalar hair, revealing unique nonmonotonic frequency behaviors and waveform features that differ from classical Kerr black holes.

Contribution

It introduces analysis of EMRIs in scalar-hairy Kerr black hole spacetimes, highlighting novel orbital and waveform features caused by scalar hair effects.

Findings

Frequencies can exhibit nonmonotonic behavior, including backward chirps.

Signals may fall below LISA's sensitivity range due to scalar hair effects.

Waveforms show unique features like periodic rest states in geodesic motion.

Abstract

In this work we analyze some judiciously chosen solutions of Kerr Black Holes with Scalar Hair (KBHsSH) of special interest for Gravitational Wave (GW) events originated from Extreme Mass Ratio Inspirals (EMRIs). Because of the off-center distribution of energy density, these spacetimes are warped in such a way that not all metric functions behave monotonically on the equatorial plane as in the exterior region of Kerr black holes (KBHs). This has great impact on the orbital parameters, which in turn affects the imprints on signals descendant from EMRIs in a adiabatic evolution. By investigating circular obit parameters, we unveil what qualitative features could be present in the signals that are new and distinct compared to KBHs, and we evolve some inspirals by employing the usual quadrupole formula approximation. We show that the frequencies of the emitted signals behave nonmonotonically, i.e. they can backward chirp, and for some particular cases they can become arbitrarily small, falling below LISA's sensibility range. Finally, we present two sets of waveforms produced by a noncircular EMRI in which the compact object (CO) follows a type of geodesic motion typically present in spacetimes with a static ring (SR), in which the compact object is periodically momentarily at rest.