Physics Colloquium - Gravitational Waves, Plasma Lenses, and Heavy Pulsars, Oh My!
Gravitational Waves, Plasma Lenses, and Heavy Pulsars, Oh My!:Science with a with a Pulsar Timing Array DetectorMichael LamAssistant ProfessorSchool of Physics and Astronomy, RITAbstract:The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration is working towards the detection and study of low-frequency gravitational waves (GWs) using an array of rapidly rotating, highly stable radio pulsars distributed across the galaxy. Each pulsar emits a radio beam that passes our line of sight and is observed as regular, pulsed emission. We measure the times of arrival of pulses and compare with a model that includes: the rotational motion of the pulsar, orbital motions, and interstellar propagation delays; random timing noise from pulsars themselves and from the interstellar medium; and a correlated GW signal. Therefore, pulsar timing array observations provide a rich data set to look at a wide variety of multi-messenger astrophysical phenomena. I will highlight areas of work being done by the NANOGrav collaboration, including the astrophysical constraints we have placed so far on the dynamics of supermassive black hole binaries at the centers of merging galaxies. I will also discuss the synergistic science obtained while we work to build our detector, such as the detection of the most-massive neutron star known to date and the observation of an interstellar plasma lens along the line of sight toward one of our most precise pulsars.Speaker Bio:Dr. Lam is an astrophysicist in the School of Physics and Astronomy. He is a member of the North American Nanohertz Observatory for Gravitational Waves, whose goal is to detect and characterize low-frequency gravitational waves coming from a variety of sources such as supermassive black hole binaries at the centers of merging galaxies. He is co-chair of the Noise Budget Working Group, whose task is to characterize noise sources in the pulsar timing array detector, optimize the the sensitivity of that detector, and correct/mitigate the various sources of noise. One large component of this work is the study of the ionized interstellar medium and as such he also uses the pulsars as tools to study a wide range of small- and large-scale phenomena in the Galactic electron content. He has recently extended this work on the interstellar medium to using Fast Radio Bursts as probes of the intergalactic medium. He also works on pulsar timing observations, gravitational wave detection methods, and cyber-infrastructure development for the collaboration. In addition, he is a heavy contributor to education and public outreach efforts and is a member of NANOGrav's Equity and Climate Committee.Intended Audience:No background knowledge required. All are welcome.
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