Stellar Explosions & Extreme Stars
Pulsars
Pulsars are rapidly spinning neutron stars whose radio beams sweep past Earth like a lighthouse.
Discovered in 1967, some pulsars keep time so steadily that they rival atomic clocks.
- Observe
A radio source that flashes with extreme regularity.
- Measure
Pulse arrival times recorded to a fraction of a microsecond.
- Model
A rotating, magnetized neutron star with beams aligned to its magnetic poles.
- Explain
A collapsed star spinning like a lighthouse.
What is it?
A pulsar is a neutron star that spins and emits beams of radiation from its magnetic poles. Because the magnetic axis is tilted from the spin axis, the beams sweep across space, and if one crosses Earth we see a pulse each rotation.
Spin periods range from about a millisecond to several seconds. Millisecond pulsars, thought to be spun up by matter from a companion star, are especially stable. Exactly how pulsars generate their radio emission is still not fully understood.
How does it happen?
- Stage 1Neutron star forms with strong magnetic field
- Stage 2It spins and emits beams from its poles
- Stage 3A beam sweeps across Earth
- Stage 4Telescopes record regular pulses
What do we actually observe?
- Regular pulses
- The period can be measured to extraordinary precision. The Crab pulsar, the remnant of the supernova seen in 1054, spins about 30 times per second.
- Slow spin-down
- Most pulsars gradually slow as they lose energy, and the rate of slowing reveals their magnetic field.
- Glitches
- Occasional sudden speed-ups provide clues about the interior.
How do scientists detect it?
- Radio telescopes. Green Bank, Parkes, FAST, MeerKAT and others find and time pulsars.
- Pulsar timing arrays. Projects such as NANOGrav time many millisecond pulsars together and have reported evidence for a background of very low-frequency gravitational waves.
- X-ray and gamma-ray telescopes. Fermi and NICER see pulsed high-energy emission.
Jocelyn Bell Burnell and Antony Hewish first detected a pulsar in 1967. The 1974 Hulse–Taylor binary pulsar later showed orbital decay matching the loss of energy to gravitational waves.
Why does it matter?
- Precise clocks for tests of general relativity and for gravitational-wave searches.
- Probes of the interstellar gas between stars, since pulses are delayed by ionized gas.
- Clues about how neutron stars are born and how radio emission is produced.
The SpaceWeatherTracker connection
When astronomers time pulsars, they must correct for the solar wind and Earth's ionosphere, the same plasma environment SpaceWeatherTracker monitors, which delays radio pulses slightly.
Related phenomena
Primary family: Stellar Explosions & Extreme Stars
Pulsars: common questions
What is a pulsar?
A rotating neutron star whose beams of radiation sweep across Earth, producing regular pulses.
Do pulsars actually pulse?
No. The star emits steadily; the pulses appear because the rotating beam points toward Earth once per turn.