Higher Harmonics of Double White Dwarfs in the Centihertz Band: Linking LISA and DECIGO

TL;DR

This paper explores how future space-based gravitational wave observatories like DECIGO can detect higher harmonics from double white dwarf binaries, providing insights into their properties and complementing LISA's capabilities.

Contribution

It demonstrates that while LISA can only detect higher harmonics in rare cases, planned decihertz detectors will routinely observe these signals, enabling better understanding of binary systems.

Findings

LISA detects higher harmonics only in rare nearby systems.

DECIGO can detect the third harmonic in about 10% of inspiral binaries.

Higher harmonics enable constraints on mass ratios of white dwarf binaries.

Abstract

We investigate the detectability of post-Newtonian higher harmonics from Galactic double white dwarfs in the centihertz band ($\sim 0.01$ Hz). Using a synthetic population, we show that, unlike the quadrupole mode, higher harmonics remain undetectable with LISA except for rare nearby systems. In contrast, planned mid-band (decihertz) observatories such as DECIGO and BBO will be able to detect the third harmonic for about 10\% of inspiral binaries above $\sim 5$ mHz, enabling statistical constraints on mass ratios. These results highlight the successive roles of LISA and future decihertz missions in establishing a coherent strategy for space-based gravitational-wave astronomy.