In the summer of 1967, a 24-year-old graduate student at Cambridge University noticed something peculiar in miles of chart recorder paper. A persistent, rhythmic radio signal pulsed with astonishing regularity, once every 1.337 seconds. The signal was too fast and too regular to come from any known natural source, and for a brief, exciting moment, the research team half-seriously labeled it “LGM-1,” for “Little Green Men.” But Jocelyn Bell Burnell had not found aliens. She had discovered pulsars, rapidly rotating neutron stars that would open an entirely new window on the universe.
The discovery of pulsars ranks among the most important astronomical findings of the twentieth century. It confirmed the existence of neutron stars, provided natural laboratories for testing general relativity and nuclear physics under extreme conditions, and earned the 1974 Nobel Prize in Physics. But the prize went to Bell Burnell’s supervisor, Antony Hewish, and radio astronomer Martin Ryle, not to the graduate student who actually found the signal, sparking one of the most debated Nobel decisions in history.
Early Life and Education
Susan Jocelyn Bell was born on July 15, 1943, in Lurgan, Northern Ireland. Her father, an architect who helped design the Armagh Planetarium, encouraged her interest in science from an early age. She grew up visiting the planetarium and reading its library of astronomy books.
Overcoming Educational Barriers
Bell’s path to science was not straightforward. At age eleven, she failed the eleven-plus examination, the British test that determined whether children attended academic or vocational secondary schools. Her parents sent her to a Quaker boarding school in England, where she thrived academically and developed the persistence that would characterize her scientific career.
She earned her bachelor’s degree in physics from the University of Glasgow in 1965, one of the few women in her class. She then moved to Cambridge to pursue a Ph.D. under the supervision of Antony Hewish, who was building a new radio telescope designed to detect quasars through their rapid intensity variations (scintillation).
Building the Telescope
The Interplanetary Scintillation Array
Bell Burnell’s first task at Cambridge was helping to build the Interplanetary Scintillation (IPS) Array, a radio telescope covering an area of 4.5 acres. The construction involved hammering over a thousand posts into the ground and stringing more than 120 miles of wire and cable between them. Bell Burnell, along with other students, spent two years on this physically demanding work.
Analyzing the Data
Once operational, the telescope produced about 96 feet of chart recorder paper every day. Bell Burnell’s job was to analyze this output by hand, searching for the rapid fluctuations (scintillation) of quasars among a vast background of radio noise. She became intimately familiar with the telescope’s output, learning to distinguish genuine signals from interference caused by television transmitters, car ignition systems, and other terrestrial sources.
The Discovery
A Bit of “Scruff”
In August 1967, Bell Burnell noticed a small section of unusual signal on the chart paper, a patch of “scruff” that did not look like either quasar scintillation or known interference. The signal appeared at the same sidereal time (the same position relative to the stars) night after night, suggesting an astronomical origin rather than terrestrial interference.
Resolving the Signal
When the telescope was configured for higher time resolution in November 1967, the scruff resolved into a series of regular pulses separated by exactly 1.337 seconds. Nothing in nature was known to produce such precisely timed radio signals. The regularity was comparable to a laboratory oscillator, suggesting either an unknown natural phenomenon or, conceivably, an artificial signal.
Little Green Men?
The possibility of extraterrestrial intelligence was considered seriously, if briefly. The research team labeled the source LGM-1 (Little Green Men 1). Bell Burnell later recalled feeling annoyed at the prospect: “Here was I trying to get a Ph.D. out of a new technique, and some silly lot of little green men had to choose my frequency and my aerial to communicate with us.”
The Second Pulsar
The extraterrestrial hypothesis was effectively ruled out when Bell Burnell discovered a second pulsing source in a completely different part of the sky, followed quickly by a third and fourth. It was extremely unlikely that multiple alien civilizations would all be transmitting on the same frequency with similar pulse characteristics. The signals had to be natural.
What Are Pulsars?
Neutron Stars
Within months of the discovery’s publication in February 1968, theorists identified pulsars as rapidly rotating neutron stars. These incredibly dense objects form when massive stars exhaust their nuclear fuel and collapse. The core compresses until protons and electrons merge into neutrons, creating a sphere roughly 20 kilometers across but containing more mass than the Sun.
The Lighthouse Model
Pulsars emit beams of radio waves from their magnetic poles. Because the magnetic and rotational axes are typically misaligned, these beams sweep through space like a lighthouse beam. When a beam sweeps across Earth, radio telescopes detect a pulse. The extreme regularity of the pulses reflects the neutron star’s rotation, which is remarkably stable due to the enormous angular momentum of the compact object.
Extreme Physics
Pulsars provide natural laboratories for studying physics under conditions impossible to create on Earth:
- Density: A teaspoon of neutron star material would weigh about a billion tons
- Magnetic fields: Pulsar magnetic fields can be trillions of times stronger than Earth’s
- Gravity: Surface gravity is roughly 200 billion times Earth’s
- Rotation: Millisecond pulsars spin hundreds of times per second
Scientific Impact of Pulsars
Testing General Relativity
In 1974, Russell Hulse and Joseph Taylor discovered a binary pulsar (two neutron stars orbiting each other). Precise timing of its pulses revealed that the orbit was shrinking exactly as Einstein’s general relativity predicted, due to energy loss through gravitational radiation. This provided the first indirect evidence for gravitational waves, earning Hulse and Taylor the 1993 Nobel Prize.
Gravitational Wave Detection
Arrays of millisecond pulsars are now used as galaxy-scale gravitational wave detectors. By monitoring tiny variations in pulse arrival times from pulsars across the sky, astronomers can detect the stretching and compression of spacetime caused by gravitational waves from supermassive black hole mergers. In 2023, several pulsar timing array collaborations announced evidence for a gravitational wave background permeating the universe.
Navigation and Timekeeping
Millisecond pulsars are among the most stable natural clocks in the universe, rivaling atomic clocks in precision. NASA has explored using pulsar signals for autonomous spacecraft navigation in deep space, where GPS signals are unavailable.
The Nobel Prize Controversy
The 1974 Award
When the 1974 Nobel Prize in Physics was awarded for the pulsar discovery, it went to Antony Hewish (Bell Burnell’s supervisor) and Martin Ryle (for aperture synthesis techniques in radio astronomy). Bell Burnell was not included.
Debate and Response
The omission sparked immediate controversy. Fred Hoyle publicly criticized the decision, arguing that Bell Burnell deserved recognition for making the actual discovery. Others noted that graduate students rarely receive Nobel Prizes and that Hewish had designed the telescope and research program.
Bell Burnell herself has been remarkably gracious about the decision, saying she believes Nobel Prizes are generally not given to students and that she has benefited from the attention the controversy brought her. Nevertheless, the episode has become a prominent example in discussions about recognition of women in science and the credit dynamics between supervisors and junior researchers.
Later Recognition
Bell Burnell has received extensive recognition beyond the Nobel:
- Commander of the Order of the British Empire (1999)
- Dame Commander of the Order of the British Empire (2007)
- Special Breakthrough Prize in Fundamental Physics (2018, $3 million, which she donated entirely to fund scholarships for underrepresented physics students)
- President of the Royal Astronomical Society (2002-2004)
- President of the Institute of Physics (2008-2010)
Advocacy for Diversity in Science
Bell Burnell has become a prominent advocate for increasing diversity in physics and astronomy. She has spoken openly about the challenges she faced as a woman in science, from feeling like an impostor at Cambridge to being photographed for newspaper articles in poses she found inappropriate.
Her donation of the entire $3 million Breakthrough Prize to fund scholarships for women, ethnic minorities, and refugee students pursuing physics demonstrates her commitment to opening doors for others. “I don’t want or need the money myself,” she explained, “and it seemed to me that this was perhaps the best use I could put it to.”
Pulsars and the History of Astronomy
The discovery of pulsars belongs to a long tradition of unexpected astronomical findings. The history of astronomy is filled with discoveries that challenged existing understanding, from Galileo’s observation of Jupiter’s moons to the discovery of cosmic microwave background radiation. Discovering the History of Astronomy traces this tradition through the foundational works of Copernicus, Brahe, Kepler, and Galileo, the astronomers who built the framework within which modern discoveries like pulsars are understood.
The physics governing neutron stars connects directly to both quantum mechanics and general relativity. The quantum mechanical Pauli exclusion principle provides the degeneracy pressure that supports neutron stars against gravitational collapse, while general relativity describes the extreme spacetime curvature around these dense objects. Einstein’s Relativity presents the gravitational theory whose predictions pulsars have so beautifully confirmed.
The tradition of women in science, to which Bell Burnell belongs, is celebrated in Women on the Moon Posters, featuring the women pioneers whose names appear on the lunar surface, a fitting connection for an astronomer who expanded our understanding of the cosmos.
A Signal That Changed Astronomy
Jocelyn Bell Burnell’s discovery of pulsars opened an entirely new field of astrophysics. Those regular radio pulses, initially mistaken for possible alien signals, revealed the existence of neutron stars and provided tools for testing fundamental physics under conditions impossible to reproduce in any laboratory.
Bell Burnell’s story illustrates both the excitement and the inequities of scientific discovery. A diligent graduate student, analyzing miles of chart paper by hand, noticed an anomaly that others might have dismissed as interference. Her persistence and careful observation led to one of the century’s most important astronomical discoveries. That she did not share in the Nobel Prize for this discovery remains controversial, but her scientific legacy is beyond dispute.
Today, thousands of pulsars have been discovered, and they continue to yield insights into gravity, nuclear physics, and the large-scale structure of the universe. Every one of these discoveries traces back to that moment in 1967 when a young woman from Northern Ireland noticed a bit of scruff on a chart recorder and had the scientific instinct to investigate further.
No products in the cart. 