The discovery of pulsars in 1967 was a complete surprise. Antony Hewish and his student Jocelyn Bell (later Bell Burnell) were operating a large radio antenna in Cambridge, England, when they detected a celestial source of radio waves that pulsed every 1.3373 seconds. Never before had a star or galaxy, or any other astronomical phenomenon, been observed to tick like a clock.

Hewish and Bell considered a number of exotic explanations for the speed and regularity of the pulsing radio source, including the possibility that it was a beacon from an extraterrestrial civilization. Within a few years, the correct explanation emerged, which is no less exotic. A pulsar is a city-sized spinning ball of ultradense material that emits beams of radiation, which flash Earth-like lighthouse beams, as it spins.

How Pulsars Are Created

Pulsars are produced when certain types of stars stop producing energy and collapse. The attractive force of...