Detecting gravitational self-lensing from stellar-mass binaries composed of black holes or neutron stars

Abstract

We explore a unique electromagnetic signature of stellar-mass compact-object binaries long before they are detectable in gravitational waves. We show that gravitational lensing of light emitting components of a compact-object binary, by the other binary component, could be detectable in the nearby universe. This periodic lensing signature could be detected from present and future X-ray observations, identifying the progenitors of binaries that merge in the LIGO band, and also unveiling populations that do not merge, thus providing a tracer of the compact-object binary population in an enigmatic portion of its life. We argue that periodically repeating lensing flares could be observed for ∼ < 100 ks orbital-period binaries with the future Lynx X-ray mission, possibly concurrent with gravitational wave emission in the LISA band. Binaries with longer orbital periods could be more common and be detectable via single lensing flares, though with reliance on a model for the flare, testable by observations of future flares. Non-detection of such events, even with existing X-ray observations, will help to constrain the population of EM bright compact-object binaries.

Searching for gravitational waves via Doppler tracking by future missions to Uranus and Neptune

“…The number of binaries per frequency in a steady-state population, assuming circular orbits, can be estimated by assuming binaries are driven together by GW emission. Under this assumption, the fraction of binaries at frequency 𝜈 is approximately the residence time of the binary 𝜈/ 𝜈 GW ∝ 𝜈 −8/3 (Sesana et al 2005;Christian & Loeb 2017;D'Orazio & Di Stefano 2020) divided by the binary lifetime. As fiducial parameters we choose a quasar lifetime of 𝜏 𝑄 = 10 7 yr (Martini 2004), and 𝑞 = 0.3, typical of major galactic mergers (Volonteri et al 2003).…”