The LISA Gravitational Wave Foreground: A Study of Double White Dwarfs
Double white dwarfs (WDs) are expected to be a source of confusion-limited noise for the future gravitational wave observatoryLISA. In a specific frequency range, this "foreground noise" is predicted to rise above the instrumental noise and hinder the detection of other types of signals, e.g., gravitational waves arising from stellar-mass objects inspiraling into massive black holes. In many previous studies, only detached populations of compact object binaries have been considered in estimating theLISA gravitational wave foreground signal. Here, we investigate the influence of compact object detached and Roche-Lobe overflow (RLOF) Galactic binaries on the shape and strength of the LISA signal. Since >99% of remnant binaries that have orbital periods within the LISA sensitivity range are WD binaries, we consider only these binaries when calculating the LISAsignal. We find that the contribution of RLOF binaries to the foreground noise is negligible at low frequencies, but becomes significant at higher frequencies, pushing the frequency at which the foreground noise drops below the instrumental noise to >6 mHz. We find that it is important to consider the population of mass-transferring binaries in order to obtain an accurate assessment of the foreground noise on the LISA data stream. However, we estimate that there still exists a sizeable number (~11,300) of Galactic double WD binaries that will have a signal-to-noise ratio >5, and thus will be potentially resolvable withLISA. We present the LISA gravitational wave signal from the Galactic population of WD binaries, show the most important formation channels contributing to the LISA disk and bulge populations, and discuss the implications of these new findings.
The LISA gravitational wave foreground: a study of double white dwarfs. Ashley J. Ruiter, Krzysztof Belczynski, Matthew Benacquista, Shane L. Larson and Gabriel Williams Astrophysical Journal 717, 1006-1021 (2010).