Scientists Say: Pulsar

These rapidly spinning dead stars emit beams of radio waves like cosmic lighthouses

A glowing orange circle blasts two beams of purple away from it in opposite directions against a black background

This picture shows how an artist imagines a pulsar. The dead star blasts out two beams of radio waves (purple). As the pulsar spins, the radio waves sweep through space like lights from a lighthouse.


Pulsar (noun, “PUHL-sahr”)

Pulsars are dense, quickly spinning cores of dead stars that blast radio waves into space.

When a star that’s a few times as big as the sun dies, it shoots most of its mass off into space in a huge explosion. That explosion is called a supernova. But the core of the star collapses in on itself and forms an ultra-dense neutron star. All that mass clumps together under the force of gravity. That causes the dead star to spin faster, just like an ice skater pulling in their arms during a turn. Neutron stars can spin faster than the tires on a race car at top speed — anywhere from once every few seconds to hundreds of times per second. That’s millions of times faster than the Sun spins.

A pulsar is a special kind of neutron star that blasts out two beams of radio waves in opposite directions. As the dead star spins, those beams sweep through space like the lights on a lighthouse. If Earth is in the path of one of those beams, we see a flash of radio waves every time it sweeps past us. That makes the pulsar appear to pulse at very regular intervals.

This animation shows a pulsar’s radio beams (purple) sweeping through space. When one of the beams passes over Earth, the pulsar appears to flash.

Astronomer Jocelyn Bell Burnell first discovered pulsars in 1967. At first, some scientists thought the radio beams she saw might be coming from aliens. That was because the pulses were so regular. But then Bell Burnell found radio pulses coming from a different part of space, far from the first signal. It was unlikely that two groups of aliens were signaling us at the same time from so far apart, so scientists looked for a different explanation. They eventually learned the radio waves were coming from pulsars scattered throughout space.

Scientists today use pulsars to make maps of space and keep time in the cosmos. Pulsars can also be used study the fundamental laws of physics that rule the universe.

In a sentence

Scientists time the radio flashes from pulsars to look for gravitational waves.

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Skyler Ware is the 2023 AAAS Mass Media Fellow with Science News. She is a fifth-year Ph.D. student at Caltech, where she studies chemical reactions that use or create electricity. Her writing has appeared in ZME Science and the Council for the Advancement of Science Writing’s New Horizons Newsroom, among other outlets.

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