Physics Colloquium: David Nice

Join us for Physics Colloquium with David Nice, Lafayette College, "NANOGrav Millisecond Pulsar Observations and the Gravitational Wave Background." Talk at 5:30 p.m., a reception will follow.

Abstract

The Earth is constantly being buffeted by gravitational waves, likely generated by pairs of supermassive black hols orbiting each other in distant galaxies.  We know this because of the imprint these gravitational waves on signals from millisecond pulsars.  Millisecond pulsars are neutron stars that rotate hundreds of times a second.  They emit beams of radio waves that sweep through space as the pulsar rotates.  These beams can be detected by radio telescopes on Earth: As a pulsar beam sweeps past us, it can be detected as a pulse of radio waves.  By measuring these pulses over time, we can monitor the distance between the pulsar and the Earth with great precision, allowing us to detect extremely small variations in the distance, of order 100 meters or less, over time spans of many years.  I will describe the ongoing observing program of the NANOGrav Physics Frontiers Center.  We observe more than seventy pulsars once a month with some of the world's largest radio telescope.  In analysis of the first fifteen years of NANOGrav data, we have found strong evidence for a background of gravitational wave signals consistent with that expected from an ensemble of supermassive black hole binaries.  I will discuss this result along with various other astrophysical applications of our data set, including the detection of relativistic phenomena in binary pulsar orbits and the measurement of neutron star masses.

Physics