Astronomy Tea Talk

Supermassive black holes (SMBHs) are found at the centres of all galaxy bulges in the nearby Universe and have masses that scale closely with the properties of their hosts, indicating that these black holes have played a significant role in the formation and evolution of galaxies. The modern picture of galaxy evolution includes the formation of many SMBH binary systems during the hierarchical merging and growth of galaxies. These SMBH binaries produce a background of a low-frequency gravitational wave background (GWB), which can be searched for and constrained using observations of millisecond pulsars. As part of the Parkes Pulsar Timing Array (PPTA) project, we have made long-term pulse timing measurements of millisecond pulsars using the 64-metre Parkes radio telescope. In this talk, I will present a new method to constrain the strength of the GWB in pulsar timing measurements. I will then apply the method to the PPTA data to set an upper limit on the strength of the GWB that is a significant improvement on previously published results. The result will be interpreted in the context of different models for galaxy evolution. I will conclude by discussing the prospects for detecting gravitational waves with pulsars.