Jocelyn Bell's Pulsar (1968): The First Neutron Star Signal

Jocelyn Bell, a graduate student at Cambridge, discovered the first pulsar in 1967: a radio source pulsing every 1.337 seconds with clockwork regularity. The 1968 Nature paper by Antony Hewish, Bell and colleagues announced it. Pulsars turned out to be spinning neutron stars, the collapsed cores predicted in the 1930s.

The question

In the 1930s Baade and Zwicky proposed that supernovae create neutron stars, objects so dense that a star’s core is crushed into a ball of neutrons. For three decades nobody had seen one. The team at Cambridge was not looking for them at all. Bell and fellow students had built a large radio array, more than 1,000 posts strung with miles of wire across a 4.5-acre field, to study interplanetary scintillation: the twinkling of compact radio sources caused by the solar wind.

What the paper found

• A radio source, later called CP 1919, emitted short pulses every 1.337 seconds.
• The pulses arrived with remarkable regularity, far more stable than any known natural radio source.
• The signal kept time with the stars rather than with the clock on Earth, showing it came from outside the solar system.
• The team briefly considered an artificial origin before settling on a natural source.
• The pulses were soon attributed to rotating neutron stars, whose beams sweep past Earth like a lighthouse.

How they did it

The array’s output was written onto paper chart recorders, and Bell was the one reading the charts. On 28 November 1967 she noticed an odd signal from the direction of the constellation Vulpecula that did not look like scintillation or interference. It reappeared at the same place on the sky, following the stars rather than the clock, and faster recordings showed a train of evenly spaced pulses. The team checked the timing over the following weeks, ruling out sources on Earth and measuring the period precisely, before publishing in February 1968.

Why it mattered

Pulsars confirmed that neutron stars exist. Because they spin so steadily, they also became some of the most precise clocks in nature, and astronomers turned them into laboratories for gravity. The Hulse-Taylor binary pulsar found in 1974 gave the first indirect evidence for gravitational waves, and the first planets beyond the solar system were found in 1992 around a pulsar.

Antony Hewish shared the 1974 Nobel Prize in Physics with Martin Ryle. Bell was not included, an omission widely discussed ever since.

What we know now

Pulsars are now known by the thousands. China’s FAST radio telescope alone discovered more than 1,300 in its first decade, as of September 2026. Networks of pulsars are used as galaxy-sized gravitational-wave detectors: the NANOGrav 15-year results of 2023 found evidence for a background of low-frequency gravitational waves. Our guide to stars explains how neutron stars form.

Who wrote it

Antony Hewish led the project and was Jocelyn Bell’s thesis advisor; Bell made the discovery in the data and convinced him that the pulses came from the sky. In 2018 Jocelyn Bell Burnell received the $3 million Special Breakthrough Prize in Fundamental Physics and donated it to fund students from under-represented groups in physics.

Questions people ask

Who discovered pulsars?

Jocelyn Bell, then a graduate student at the University of Cambridge, discovered the first pulsar in 1967 while analyzing radio data. Her supervisor, Antony Hewish, led the project. The discovery was published in Nature in February 1968 by Hewish, Bell and three colleagues.

Why didn’t Jocelyn Bell get the Nobel Prize?

The 1974 Nobel Prize in Physics went to Antony Hewish and Martin Ryle, and Jocelyn Bell was not included, even though she made the discovery in the data. The omission has been widely discussed since. In 2018 she received the $3 million Special Breakthrough Prize and donated it to support under-represented physics students.

What is a pulsar?

A pulsar is a rapidly spinning neutron star that sweeps beams of radio waves across space. When a beam points toward Earth we see a pulse, like a lighthouse. The first pulsar, found in 1967, pulsed every 1.337 seconds. Pulsars are among the most precise natural clocks known.

Read the original

Hewish, A., Bell, S. J., Pilkington, J. D. H., Scott, P. F. and Collins, R. A. (1968). “Observation of a Rapidly Pulsating Radio Source.” Nature 217, 709-713. doi:10.1038/217709a0

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