Gravitational tuning forks and hierarchical triple systems

TL;DR

This paper investigates gravitational wave emissions from hierarchical triple systems near supermassive black holes, revealing unique signal features and resonant phenomena that serve as probes of strong-field gravity and black hole properties.

Contribution

It introduces a comprehensive framework for modeling GW signals from such systems, including effects like Doppler shifts and lensing, and uncovers resonant excitation of SMBH quasinormal modes.

Findings

GW signals exhibit Doppler, aberration, lensing, and amplitude modulations.

Resonant excitation of SMBH quasinormal modes occurs in these systems.

Energy flux into the SMBH horizon can be significant, surpassing standard EMRIs.

Abstract

We study gravitational wave (GW) emission in the strong-field regime by a hierarchical triple system composed of a binary system placed in the vicinity of a supermassive black hole (SMBH). The LIGO-Virgo collaboration recently reported evidence for coalescences with this dynamical origin. These systems are common in galactic centers and thus are a target for the space-based LISA mission as well as other advanced detectors. Doppler shifts, aberration, lensing and strong amplitude modulations are features present in the GW signal from these systems, built into our framework and with no need for phenomenological patches. We find that the binary can resonantly excite the quasinormal modes of the SMBH, as in the resonant excitation of two tuning forks with matching frequencies. The flux of energy crossing the SMBH horizon can be significant, when compared with that from standard extreme-mass-ratio inspirals. Therefore, these triple systems are an outstanding probe of strong-field physics and of the BH nature of compact objects.