Astronomy Colloquium for 2023-10-25

Series: Astronomy Colloquium
Date: Wednesday 25-Oct-2023
Time: 16:05-17:00 (4:05-5:00 pm)
Location: ATL 2400
Speaker: Dr. Megan DeCesar (George Mason University)
Title: "The Search for Nanohertz Gravitational Waves with the NANOGrav Pulsar Timing Array"

Pulsar timing arrays (PTAs) are kiloparsec-scale gravitational wave (GW) detectors composed of many millisecond pulsars (MSPs) timed over many years. A detection of quadrupolar spatial correlations in the variations in pulse arrival times would indicate the presence of a nanohertz-frequency gravitational wave (GW) signal in the timing residual data. In particular, the correlations between MSP pairs’ timing residuals are predicted to follow the Hellings-Downs correlation curve in the presence of an isotropic stochastic GW background (GWB). The most likely origin of such a GWB is thought to be a population of coalescing supermassive black hole binaries SMBHBs), but other more exotic sources like cosmic strings have been proposed. PTAs are predicted to first detect the GWB, followed by continuous waves (CWs) from individual foreground SMBHBs. GW detection by PTAs requires timing many tens, to hundreds, of MSPs with ~10-100 ns timing precision over years to decades; adequate sky coverage to sufficiently populate the Hellings-Downs curve; and for CW detection, high (~weekly) observing cadence. In this talk, I will focus primarily on the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) PTA and the International Pulsar Timing Array (IPTA). I will describe NANOGrav's analysis methods, our successful campaign to dramatically increase the size of our PTA and thus increase our GWB sensitivity, and the evidence for a GWB found in the NANOGrav 15-year Data Release as well as in our international partners' recent data releases. Finally I will discuss the ongoing efforts to produce the next fully-combined IPTA data set, which will be the most sensitive data set for nHz GWs to date, and NANOGrav's plans for further improving our PTA with future facilities, in particular the DSA-2000 and the next-generation VLA.

In-person colloquia are usually preceded by espresso and ice cream at 1:45 pm outside room PSC 1150 and are followed by an informal reception at 5:15 pm in that room. Anyone interested in talking with the speaker, or being added to the colloquium announcement email list, should contact the colloquium organizer Dr. Leslie Sage. Lunch will normally be reserved for the speaker to talk to graduate students. Anyone asking a question during a talk is asked to raise their hand and be acknowledged before speaking. Contact Dr. Leslie Sage for details.

Colloquium Organizer: Dr. Leslie Sage


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


Directions and information about parking can be found here.

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