Observing Gravitational Waves from the First Generation of Black Holes

The properties of the first generation of black-hole seeds trace and distinguish different models of formation of cosmic structures in the high-redshift universe. The observational challenge lies in identifying black holes in the mass range ∼ 100 − 1000M⊙ at redshift z ∼ 10. Here we show that future groundbased laser interferometers could observe gravitational waves produced by the coalescence of the first generation of light seed black-hole binaries and provide, possibly unique, information on the evolution of structures in this era. Using galaxy merger trees and four different models of black hole accretion we find that future detectors could study a few to a few tens of seed black-hole merger events in three years. We show further that a network of detectors will be able to measure the luminosity distance to typical sources to a precision of ∼ 30%, allowing us to be confident of the high-redshift nature of the sources. Subject headings: black hole physics – gravitational waves