Cambridge graduate student's 1967 discovery of pulsars began as 'little green men' signal

August 30, 2026 at 04:00 AM2 min

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In 1967, Cambridge graduate student Jocelyn Bell Burnell detected a radio signal pulsing every 1.3 seconds while analyzing data from a telescope array built to study quasars. The signal's mechanical regularity led her and supervisor Antony Hewish to jokingly label it LGM-1, for 'little green men'. The hypothesis was abandoned after Bell Burnell found a second, unrelated pulsing source elsewhere in the sky.

Key Facts

Jocelyn Bell Burnell was a doctoral student at Cambridge when she detected the signal in 1967.
The telescope array, designed by Antony Hewish, covered roughly four acres with more than 4,000 dipole antennas.
The signal pulsed every 1.3 seconds, a regularity unknown in any natural celestial object at the time.
Bell Burnell and Hewish labeled the source LGM-1, for 'little green men', on the chart itself.
The little green men hypothesis was abandoned after Bell Burnell found a second pulsing source in a different part of the sky.

The Discovery

Jocelyn Bell Burnell spent nearly two years helping build the radio telescope array at Cambridge before the discovery. By 1967, her job involved examining a hundred feet of chart paper every few days for unusual signals. She noticed a faint, repeating mark she called 'scruff' on the chart, which she recognized only because of her familiarity with ordinary noise. When she pointed the telescope back at the same patch of sky, the source ticked out pulses one and a third seconds apart.

The Little Green Men Hypothesis

Stars flicker and galaxies vary slowly, but nothing natural known in 1967 kept a beat as clean as the detected signal. Bell Burnell and her supervisor Antony Hewish half-jokingly labeled the source LGM-1, for little green men, on the chart itself. She explained that the shorthand was easier than saying 'you know that funny pulsing source at right ascension 1919, declination plus 20'.

Hypothesis Abandoned

The joke lasted only until Bell Burnell found a second, completely different ticking signal elsewhere in the sky. She explained decades later that the second source 'finally scotched the little green men hypothesis'. It was highly unlikely that two lots of little green men on opposite sides of the universe would both signal Earth at the same time using a daft technique and a commonplace frequency.