Pulsars are ultra-dense, rapidly spinning, and highly magnetized remnants of dead stars. They act like cosmic lighthouses, sending out regular pulses of radio waves and sometimes gamma rays in beams that sweep across the sky. A special class called millisecond pulsars spins hundreds of times per second and is among the most precise clocks in the universe. For decades, astronomers believed that a pulsar's radio signals are only produced close to the star's surface, near its magnetic poles.