Gravitational Waves from the Remnants of the First Stars

TL;DR

This paper models the formation of the first stars and predicts their black hole merger signals detectable by gravitational wave observatories, providing insights into primordial star populations and their impact on GW detection.

Contribution

It introduces a semi-analytical, cosmologically consistent model for primordial star formation and estimates their gravitational wave signatures, linking GW observations to early universe star properties.

Findings

Primordial star remnants can produce detectable GW signals.

Estimated ~1 primordial BH-BH merger per year for aLIGO.

Detection of massive mergers could constrain the primordial IMF.

Abstract

Gravitational waves (GWs) provide a revolutionary tool to investigate yet unobserved astrophysical objects. Especially the first stars, which are believed to be more massive than present-day stars, might be indirectly observable via the merger of their compact remnants. We develop a self-consistent, cosmologically representative, semi-analytical model to simulate the formation of the first stars. By extrapolating binary stellar-evolution models at 10% solar metallicity to metal-free stars, we track the individual systems until the coalescence of the compact remnants. We estimate the contribution of primordial stars to the merger rate density and to the detection rate of the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). Owing to their higher masses, the remnants of primordial stars produce strong GW signals, even if their contribution in number is relatively small. We find a probability of $\gtrsim1\%$ that the current detection GW150914 is of primordial origin. We estimate that aLIGO will detect roughly 1 primordial BH-BH merger per year for the final design sensitivity, although this rate depends sensitively on the primordial initial mass function (IMF). Turning this around, the detection of black hole mergers with a total binary mass of $\sim 300\,\mathrm{M}_\odot$ would enable us to constrain the primordial IMF.