Vikram Ravi (University of Melbourne/CASS)

Vikram Ravi: What gravitational-wave observations can tell us about the super-massive black hole population

Marsfield Lecture Theatre

Abstract

Title: What gravitational-wave observations can tell us about the super-massive black hole population of the Universe

Abstract: Around 0.3% of the mass of the most massive galaxies in the nearby Universe is contained in super-massive black holes (SMBHs). Through cosmic time, the growth of SMBHs through accretion strongly influences star formation processes in their host galaxies. Galaxy mergers, which are also integral to the present-day properties of the massive galaxy population, are expected to result in coalescences of the central SMBHs. Binary SMBHs, in the process of coalescing, emit gravitational wave signals which depend only on the SMBH masses, distances, and orbital characteristics. These gravitational wave signals are being searched for in long-term radio timing measurements of millisecond pulsars, for example by the Parkes Pulsar Timing Array project. In this end-of-PhD exposition, I will describe the expected nature of the summed gravitational wave signals from binary SMBHs, highlighting the effects of key astrophysical unknowns. I will then show what pulsar timing measurements can do, and indeed are doing, to boldly confront these unknowns, and hence fill some important blanks in our understanding of the co-evolution of SMBHs and galaxies.