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The Crab Nebula and its central pulsar (Chandra X-ray + Hubble optical composite)
The Crab Nebula and its central pulsar (Chandra X-ray + Hubble optical composite). Photo: NASA/CXC/ASU/J. Hester et al.; NASA/HST/ASU/J. Hester et al. · Public domain · via Wikimedia Commons
Science & space · Cambridge, UK · 1967

The Discovery of Pulsars

Established1967 CE – 1968 CEMullard Radio Astronomy Observatory, Cambridge

A signal ticking every 1.337 seconds — briefly nicknamed 'Little Green Men.'

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In 1967, Jocelyn Bell, a graduate student at Cambridge, noticed a strange signal in her radio-telescope charts. Resolved with a faster recorder, it turned out to be a train of pulses spaced precisely 1.337 seconds apart. The regularity was so striking that the team half-jokingly labeled it LGM-1, for 'Little Green Men.'

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How to read the labels

EstablishedSupported by strong, converging evidence.
ContestedEvidence exists but qualified scholars disagree.
UnresolvedThe question is open; evidence does not settle it.
LegendComes from myth, literature or tradition, not physical evidence.
SpeculativeA hypothesis with little direct evidence so far.

Hero image: The Crab Nebula and its central pulsar (Chandra X-ray + Hubble optical composite). Photo: NASA/CXC/ASU/J. Hester et al.; NASA/HST/ASU/J. Hester et al. · Public domain · via Wikimedia Commons. Evidence labels describe the written claims, not the image. Version 1 · updated 2026-10-22.