Astrophysics & Particle Physics-APPC 2026

Pulsar timing arrays (PTAs) consist of highly stable millisecond pulsars as sensitive cosmic clocks to measure low-frequency gravitational waves. Unlike high-frequency gravitational waves measured by LIGO or Virgo, PTAs search for waves at the nanohertz level, which are generated by supermassive black hole binaries, cosmic strings, and other large-scale astrophysical events.Millisecond pulsars are neutron stars that spin hundreds of times a second, emitting radio wave beams with extraordinary consistency. By precisely tracking the arrival times of such pulses, astronomers can sense tiny deviations, referred to as timing residuals, due to gravitational waves stretching or squeezing space-time between the Earth and pulsars.PTAs work by blending observations of numerous pulsars in the sky to create a galactic-scale detector. Major collaborations are the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the European Pulsar Timing Array (EPTA), and the Parkes Pulsar Timing Array (PPTA). Combined, they create the International Pulsar Timing Array (IPTA), combining data to enhance sensitivity and coverage.

PTAs supplement other gravitational wave observatories, providing a low-frequency window into the gravitational-wave universe unavailable to ground-based detectors. By combining PTA data with electromagnetic and high-frequency gravitational waves, astronomers push the development of multi-messenger astrophysics, exploring extreme cosmic phenomena on the whole spectrum.In conclusion, pulsar timing arrays are ultra-precise astrophysical tools that convert millisecond pulsars into a galactic-sized gravitational wave detector. They offer a special means of exploring supermassive black hole mergers, cosmic gravitational wave backgrounds, and physics at its most fundamental level, opening a new avenue in understanding the universe.