What Is A Pulsar?
QUICK ANSWER
A pulsar is a rapidly spinning neutron star that emits beams of radiation from its magnetic poles. As the pulsar rotates, these beams sweep across space like a lighthouse. When a beam crosses Earth, we detect it as a regular pulse of radiation. Over 3,000 pulsars have been discovered since 1967.
Pulsars are some of the most remarkable objects in the universe. They're neutron stars (the dense remnants of massive stars that exploded as supernovae) that spin rapidly and emit beams of radiation. The first one was discovered in 1967 by Jocelyn Bell Burnell, who initially nicknamed the mysterious signals LGM (Little Green Men) due to their precision. Pulsars are now understood as natural cosmic lighthouses.
How do pulsars work?
Like cosmic lighthouses. According to NASA, pulsars are neutron stars (the very dense remnants of a dead star) that are highly magnetic and rotate rapidly as they emit beams of radiation, generally from the vicinity of their magnetic poles. As the pulsar spins around on its axis, it sweeps a beam of radiation around the cosmos like a turning lighthouse. From Earth, we see the beam as it sweeps rapidly past as a pulse of radiation. Not every neutron star appears as a pulsar; we only see those whose beams happen to cross Earth's line of sight.
How fast do they spin?
Some spin hundreds of times per second. NASA reports that astronomers have discovered over 3,000 pulsars so far. The fastest can spin hundreds of times per second and are called millisecond pulsars, while the slowest can take almost 6.7 hours to rotate just once. Young pulsars typically spin faster and slow down over time as they radiate away their rotational energy. Millisecond pulsars are usually very old pulsars in binary systems, where mass falling from a companion star has spun them up to extreme speeds.
When were they discovered?
1967 by Jocelyn Bell Burnell. While working on her doctorate at the University of Cambridge, Bell Burnell noticed a periodic, pulsating signal in radio observations of the constellation Vulpecula. She nicknamed the signals LGM for Little Green Men, joking that the timing was too precise to be natural. Astrophysicists Franco Pacini, Thomas Gold, and others soon identified pulsars as rotating neutron stars. The 1974 Nobel Prize for the discovery went to Bell Burnell's supervisor Antony Hewish, controversially leaving out Bell Burnell herself.
Why are they important?
They're cosmic clocks and physics laboratories. Pulsars are extraordinarily precise natural clocks; millisecond pulsars rival atomic clocks in stability. Astronomers use them to test general relativity in extreme gravity, detect gravitational waves through pulsar timing arrays, and map the interstellar medium. The Crab Nebula pulsar (from the 1054 CE supernova) has been observed for decades. The brightest known pulsar, NGC 5907 ULX, emits as much energy per second as the Sun produces in three and a half years.
A pulsar is a rapidly spinning neutron star that emits beams of radiation from its magnetic poles. As it rotates, the beams sweep across space like a lighthouse, appearing as regular pulses when they cross Earth. Over 3,000 pulsars have been discovered since 1967, when Jocelyn Bell Burnell first detected one. Pulsars range from millisecond rotators to slow 6.7-hour rotators and serve as precise cosmic clocks for testing physics and detecting gravitational waves.
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