Publication Date:
2016-07-15
Description:
The recent discovery of the gravitational wave source GW150914 has revealed a coalescing binary black hole (BBH) with masses of ~30 M . Previous proposals for the origin of such a massive binary include Population III (PopIII) stars. PopIII stars are efficient producers of BBHs and of a gravitational wave background (GWB) in the 10–100 Hz band, and also of ionizing radiation in the early Universe. We quantify the relation between the amplitude of the GWB ( gw ) and the electron scattering optical depth ( e ), produced by PopIII stars, assuming that f esc 10 per cent of their ionizing radiation escapes into the intergalactic medium. We find that PopIII stars would produce a GWB that is detectable by the future O5 LIGO/Virgo if e 0.07, consistent with the recent Planck measurement of e = 0.055 ± 0.09. Moreover, the spectral index of the background from PopIII BBHs becomes as small as dln gw /dln f 0.3 at f 30 Hz, which is significantly flatter than the value ~2/3 generically produced by lower redshift and less-massive BBHs. A detection of the unique flattening at such low frequencies by the O5 LIGO/Virgo will indicate the existence of a high-chirp mass, high-redshift BBH population, which is consistent with the PopIII origin. A precise characterization of the spectral shape near 30–50 Hz by the Einstein Telescope could also constrain the PopIII initial mass function and star formation rate.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
