The Leonard E Parker Center for Gravitation, Cosmology and Astrophysics holds frequent seminars on a broad range of ongoing cosmology and gravitation research topics. Unless otherwise noted, seminars are on Friday afternoons at 1:00 PM in KIRC 2175; there is a gathering for a brown bag lunch at 12:30.

Measuring Gravitational Wave Memory with Pulsar Timing Array Experiments
Kristina Islo Research Assistant, UWM Dept. of Physics

The general theory of relativity predicts the emission of gravitational waves (GWs) during mergers of massive objects, such as two supermassive black holes. At the moment of coalescence of a supermassive black hole binary (SMBHB), a burst of gravitational radiation is predicted to be accompanied by a non-oscillatory waveform called memory. Generally it is thought that the detection likelihood of individual memory events is small, particularly when compared to the strength of the ensemble stochastic background from inspiralling SMBHBs, and the comparatively larger detection probability of discrete inspiralling SMBHB signals. However, a population of coalescing SMBHBs distributed throughout the Universe will also form a “memory background” that is produced by the ensemble addition of memory from SMBHB coalescences. Such a background could be detected in the micro-nanohertz frequency band using the observed arrival times of beamed radio wave emission from millisecond pulsars. Using well-studied pulsars to observe GWs, a technique known as pulsar timing arrays, can help us to better characterize low-frequency GW sources and the astrophysics governing their evolution. By modeling the memory background with simulated populations of coalescing SMBHBs, we can predict the strength and distribution of the characteristic strain spectrum, as well as constrain astrophysical parameters. My talk will focus on the results of these memory simulations, and elaborate on how they inform our understanding of coalescence rates, source populations, and binary-environment coupling.