Physics Professors’ Research Finds Possible ‘First Hints’ of Low-Frequency Gravitational Waves
Dr. Paul Baker, an assistant professor of physics, co-authored an article in The Astrophysical Journal Letters based on data gathered and analyzed over 13 years by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). The published findings, “The NANOGrav 12.5-year Data Set: Search For An Isotropic Stochastic Gravitational-Wave Background,” shows an intriguing low-frequency signal that may be attributable to gravitational waves from merging supermassive black holes in other galaxies.
NANOGrav researchers studying the signals from distant pulsars – small, dense stars that rapidly rotate, emitting beamed radio waves, much like a lighthouse – have used radio telescopes to collect data that may indicate the effects of gravitational waves.
Gravitational waves are ripples in space-time caused by the movements of incredibly massive objects, such as black holes orbiting each other or neutron stars colliding. Astronomers cannot observe these waves with a telescope like they do stars and galaxies. Instead, they measure the effects passing gravitational waves have, namely tiny changes to the precise position of objects - including the position of the Earth.
But gravitational waves can interrupt this observed regularity, as the ripples cause space-time to undergo tiny amounts of stretching and shrinking. Those ripples result in extremely small deviations in the expected times for pulsar signals arriving on Earth. Such deviations indicate that the position of the Earth has shifted slightly.
By studying the timing of the regular signals from many pulsars scattered over the sky at the same time, known as a “pulsar timing array,” NANOGrav works to detect minute changes in the Earth’s position due to gravitational waves stretching and shrinking space-time.
These newest findings set up direct detection of gravitational waves as the possible next major step for NANOGrav and other members of the International Pulsar Timing Array (IPTA), a collaboration of researchers using the world’s largest radio telescope. Baker has been a member of NANOGrav since 2016.