The Discovery of Pulsars

Neutron stars are real

First published: A. Hewish, S. J. Bell, J. D. H. Pilkington, P. F. Scott, R. A. Collins, "Observation of a Rapidly Pulsating Radio Source", *Nature* 217 (1968): 709–713.

Bell Burnell's array picks up a regular radio pulse every 1.337 seconds. After ruling out interference and "little green men," the explanation: rotating neutron stars.

In November 1967, Bell Burnell, then a graduate student at Cambridge, identified a strange signal in radio data from a new interplanetary scintillation array: a series of sharp pulses spaced exactly 1.337 seconds apart, from a fixed direction in the sky. The signal was too regular to be natural under existing models; it was briefly designated LGM-1 ("Little Green Men"). After identifying three more such sources and ruling out intelligent origin, the team proposed (and theorists soon confirmed) the explanation: rapidly rotating neutron stars whose magnetic poles sweep a radio beam across Earth. The discovery confirmed neutron stars (a 1934 theoretical prediction by Baade and Zwicky) as real astrophysical objects and opened the field of high-density astrophysics. Hewish received the 1974 Nobel Prize; the controversial omission of Bell Burnell remains debated.