Coupling of Dual Mass-Transferring White-Dwarf Binaries as a Variable Gravitational-Wave Emitter

TL;DR

This paper investigates a hierarchical four-body system of mass-transferring white dwarf binaries, revealing a limit cycle and beat effects in gravitational wave emissions that could be detectable by space-based detectors.

Contribution

It introduces a simplified model showing that such four-body systems can settle into a limit cycle, causing observable amplitude variations in gravitational waves.

Findings

System can reach a limit cycle with small period gap

Amplitude variation in gravitational waves due to beat effect

Beat period could be 1-10 years, detectable by space GW detectors

Abstract

We study evolution of a hierarchical four-body (2+2) system composed by a pair of mass-transferring white dwarf binaries. Applying a simplified model around the synchronous state of two inner orbital periods, we newly find that the four body system could settle down to a limit cycle with a small period gap. The period gap generates an amplitude variation of emitted gravitational waves, as a beat effect. Depending on model parameters, the beat period could be 1-10 yr and a large amplitude variation might be observed by space gravitational-wave detectors.