The NANOGrav Physics Frontiers Center

This Physics Frontiers Centers (PFC) award to the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) supports their focus on the direct detection and characterization of low-frequency gravitational waves (GW), in the nanohertz regime, some eleven orders of magnitude smaller than the GW already detected by the Laser Interferometer Gravitational-wave Observatory (LIGO); these two NSF-supported experiments are highly complementary. NANOGrav carries out this study by monitoring the pulse arrival times of millisecond pulsars (MSPs), which are ultra-spin-stable neutron stars, and thus the most precise celestial clocks in the Universe.

GWs cause fluctuations in pulse arrival times that are correlated among different pulsars. Discovering these correlations requires the synergy of experts in gravitational physics, data analysis, and astrophysics coming together in a collaborative environment. In addition to monitoring a known list of MSPs, NANOGrav routinely discovers new MSPs to add to their study.

NANOGrav reaches large numbers of the general public through exhibits and talks, and a growing social media presence. An associated student research program reaches more than 150 undergraduate students every year, and the Pulsar Search Collaboratory involves hundreds of middle and high school students and their teachers.

The sources most likely to be detected in the nanohertz band in the near future are supermassive binary black holes that form after massive galaxies merge. In fact, NANOGrav searches so far have already placed astrophysically interesting constraints on the evolution of galaxies and their supermassive black holes. Other sources include cosmic strings, phase transitions in the early universe, and relic GW from inflation; detecting any of these would be transformative.

GW observations can also be used to investigate the origin of cosmic acceleration and the conflict between quantum mechanics and general relativity, two of the most profound challenges currently facing fundamental physics. Apart from GW, NANOGrav observations enable high-impact synergistic science, including constraining the dense matter equation of state, making dynamical tests of general relativity, further understanding the ionized interstellar medium, and discovering exotic neutron star systems and radio transients.

This Physics Frontiers Centers award is co-funded by the Physics Frontiers Centers Program in the Division of Physics and the Mid-scale Innovations Program in the Division of Astronomical Sciences. This project advances the goals of the NSF Windows on the Universe Big Idea.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.