Phenomena · Space Codex
Pulsars
Spinning neutron stars whose beams sweep past Earth like a lighthouse.
Cosmic lighthouses
At a glance
Key points
The fastest spins 716 times a second.
- The fastest spins 716 times a second
- 4,393 catalogued
- Timing them found the first exoplanets
Little green men
In 1967 Jocelyn Bell Burnell, a PhD student at Cambridge, spotted a small patch of 'scruff' on the chart records of a new radio array. On 28 November faster recordings resolved it into sharp pulses 1.337 seconds apart, so regular that the source was half-jokingly labelled LGM-1, for 'little green men', until similar sources turned up elsewhere in the sky. Her supervisor Antony Hewish shared the 1974 Nobel Prize in Physics; her omission is still widely discussed.
Why they pulse
A pulsar's magnetic axis is tilted from its spin axis, so beams from its magnetic poles sweep round the sky. We see pulses only if a beam crosses Earth, so many pulsars are invisible to us. Young pulsars gradually slow as they radiate away rotational energy. Old ones in binary systems can be 'recycled', spun up to hundreds of turns per second by gas falling onto them from a companion star.
Clocks in space
Millisecond pulsars keep time rivalling atomic clocks. Timing them revealed the first exoplanets in 1992 and is now used to listen for low-frequency gravitational waves.
Testing Einstein
The orbit of the Hulse–Taylor binary pulsar shrinks at the rate general relativity predicts for a system losing energy as gravitational waves, matching to better than half a percent. It was the first evidence that such waves exist, decades before LIGO heard one directly. In 2023 pulsar timing arrays reported a faint background of nanohertz waves, most likely from pairs of supermassive black holes, though that origin is not yet confirmed.
On screen
A real pulsar spins far too fast for a 60-frame-per-second display, so any animation must slow it down hundreds of times.
Related entries
- Neutron starsCity-sized stellar cores
- Crab NebulaM1 · the wreck of the supernova of 1054
- PSR B1257+12 planetsThe first exoplanets ever confirmed
Sources
- ATNF Pulsar Catalogue history (opens in a new tab)
- Hessels et al. 2006, Science (arXiv) (opens in a new tab)
- Chandra: Crab Nebula (opens in a new tab)
- Chandra: Vela pulsar (opens in a new tab)
- NASA Imagine the Universe: neutron stars (opens in a new tab)
- Hewish, Bell et al. 1968, Nature 217:709 (opens in a new tab)
- Nobel Prize in Physics 1993: press release (opens in a new tab)
- NANOGrav 15-year data set, ApJL 2023 (arXiv) (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.