Gravitational wave spectral synthesis

Abstract

ABSTRACT We study the Laser Interferometer Space Antenna (LISA) sources that arise from isolated binary evolution, and how these depend on age and metallicity, using model stellar populations from bpass. We model these as single-aged populations which are analogous to star clusters. We calculate the combined gravitational wave (GW) spectrum of all the binaries within these model clusters, including all types of compact binaries as well as those with living stars. These results allow us to evaluate the detectability of star clusters with LISA. We find at late times the dominant sources are WD–WD binaries by factors of 50–200, but at times between 108 and 109 yr we find a significant population of NS–WD and BH–WD binaries (2–40 per 106 M⊙), which is related to the treatment of mass transfer and common-envelope events in bpass, wherein mass transfer is relatively likely to be stable. Metallicity also has an effect on the GW spectrum and on the relative dominance of different types of binaries. Using the information about known star clusters will aid the identification of sky locations where one could expect LISA to find GW sources.