Many neutron stars emit beams of electromagnetic radiation from their magnetic poles. If a beam sweeps past Earth, we detect regular pulses — earning these objects the name pulsars. When pulsars were first detected in 1967 by Jocelyn Bell Burnell, the signals were so regular that scientists briefly considered they might be alien communications.

Pulsars are the most precise natural clocks in the universe. The fastest known, PSR J1748-2446ad, rotates 716 times per second. Pulsar timing is so accurate that it can detect gravitational waves — tiny ripples in spacetime.