Multiband gravitational-wave event rates and stellar physics

Abstract

Joint gravitational-wave detections of stellar-mass black-hole binaries by ground-and space-based observatories will provide unprecedented opportunities for fundamental physics and astronomy. We present a semianalytic method to estimate multiband event rates by combining selection effects of ground-based interferometers (like LIGO/Virgo) and space missions (like LISA). We forecast the expected number of multiband detections first by using information from current LIGO/Virgo data, and then through population synthesis simulations of binary stars. We estimate that few to tens of LISA detections can be used to predict mergers detectable on the ground. Conversely, hundreds of events could potentially be extracted from the LISA data stream using prior information from ground detections. In general, the merger signal of binaries observable by LISA is strong enough to be unambiguously identified by both current and future ground-based detectors. Therefore thirdgeneration detectors will not increase the number of multiband detections compared to LIGO/Virgo. We use population synthesis simulations of isolated binary stars to explore some of the stellar physics that could be constrained with multiband events, and we show that specific formation pathways might be overrepresented in multiband events compared to ground-only detections.

Primordial black hole merger rates: distributions for multiple LIGO observables

“…The angular dependence of the detection probability may be well approximated by the function p(ω) [24], with the detection probability given by…”

“…Additional observables could also be used to distinguish between mergers of primordial and astrophysical origin. A recent paper by Gerosa et al [24] obtained merger rate distributions for astrophysical black holes against three observables: the total mass M , redshift z, and the mass ratio q. It is desirable to have the same distributions for PBHs so a comparison between the primordial and astrophysical cases can be drawn.…”

“…PBH = 10 −1 f PBH = 10 −2 f PBH = 10 −Merger rate distributions in total mass M , redshift z, mass ratio q, and chirp mass M for a lognormal mass distribution. The distributions for astrophysical black holes from[24] are shown in green for the first three plots.…”

Are stellar-mass black-hole binaries too quiet for LISA?

“…We stress that uncertainties in both R and p(ζ) affect our predictions. Gerosa et al (2019) used a sky-averaged LISA noise curve to compute SNRs. Here we perform a more generic calculation where we compute ρ as a function of θ.…”

“…We find an expected SNR threshold ρ thr ∼ 15 for systems merging within 10 yr. Previous work has assumed a threshold ρ thr ∼ 8, similar to that for compact-binary mergers in LIGO (Abbott et al 2016d), and predict a handful of multiband detections (Kyutoku & Seto 2016;Sesana 2017;Gerosa et al 2019). The expected number of events scales as ρ −3 thr .…”