Double Compact Objects as Low-frequency Gravitational Wave Sources

We study the galactic population of double compact objects (NS-NS, BH-NS, BH-BH binaries) to investigate the number (if any) of these systems that can potentially be detected with LISA at low gravitational-wave frequencies. We calculate the Galactic numbers and physical properties of these binaries and show their relative contribution from the disk, bulge and halo. It is found that, although the formation efficiency of double compact objects is very small, a few thousand of such systems should be detectable with LISA depending on the instrument low-frequency sensitivity and the efficiency of data analysis techniques for identifying highly eccentric systems. Detailed population synthesis, combined with an updated Galactic model and a realistic LISA signal simulator are used to obtain the results. We outline the prospects of the science that could be done with future LISA observations of double compact objects. And in particular, we note that LISA observations could be used to determine the fate of binaries that enter a common envelope phase while passing through Hertzsprung gap. As these binaries are the most likely progenitors of double compact objects with black holes, LISA can provide very useful limits on the evolution of massive stars. Subject headings: binaries: close — stars: evolution, neutron — gravitation