Shami Chatterjee

Millisecond pulsars, rapidly rotating neutron stars, emit narrow radio pulses that can be used for precision metrology, including the detection of low-frequency (nanohertz) gravitational waves (GWs) that alter propagation distances. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration members have built a Galaxy-scale detector for GWs by precisely timing a large number of millisecond pulsars over decade timescales, along with our international partners. I will describe some of the challenges and surprises leading up to our release of 15 years of pulsar timing data, which provides evidence for a stochastic background of low-frequency GWs. In the near term, we will have a detailed characterization of the GW spectrum, which constrains the abundance and merger rates of supermassive black hole binaries (SMBHBs) in the centers of galaxies. Longer term detection goals include anisotropy in the GW background, continuous waves from individual SMBHBs, and the memory signal from the aftermath of SMBHB mergers. I will also introduce the Deep Synoptic Array-2000, planned to be a NANOGrav workhorse when it comes on line later this decade. DSA-2000 will have capabilities exceeding those of the Arecibo radio telescope, which provided key data for the NANOGrav 15-year results.