Pulsars are neutron stars that beam radio waves like lighthouse beacons. Some spin hundreds of times per second, so steady that their pulses rival atomic clocks. By tracking tiny shifts in their arrival times, astronomers can sense ripples in spacetime from pairs of supermassive black holes millions of light‑years away.
Pulsar timing arrays work by monitoring dozens of stable pulsars scattered across the sky. A passing gravitational wave stretches and squeezes the distance between Earth and each pulsar, imprinting a telltale pattern in the residuals. Detecting that correlated hum confirms that giant black holes commonly form binaries and slowly spiral together.
The same datasets probe interstellar plasma, solar wind variability, and even the mass distribution of the asteroid belt. In each case, nanosecond‑level timing turns astrophysical nuisances into signals to be modeled and learned from.
Improved receivers and longer baselines will sharpen sensitivity. As the array grows, astronomers can start to resolve individual binaries and map out how often galaxies merge and their central black holes pair up.
Pulsars compress extreme physics—superfluid interiors, ultra‑dense matter, and ferocious magnetic fields—into stellar remnants no larger than a city. Using them as instruments may be the most elegant hack in astronomy.