First to detect pulsars, one of the most important discoveries of 20th-century astrophysics
Tenacious, pushing ahead in the face of scepticism
Gracious when her contributions were overlooked by the Nobel Committee
First female President of the Institute of Physics
Jocelyn Bell was born in 1943 in Belfast, Northern Ireland, UK. Her father was an architect for the building of the Armagh Observatory, which kindled an early interest in astronomy. This remained despite her primary school giving girls lessons in cookery and sewing instead of science – until a number of parents, hers included, objected. When she failed the 11+ exam, her parents sent her to a Quaker boarding school in England where her aptitude for physics quickly became apparent.
After gaining a degree in physics at Glasgow University, she went on to Cambridge to carry out Phd research on quasars (very distant, highly luminous astronomical objects that had only recently been detected) under her thesis supervisor Antony Hewish. Together they constructed and operated an 81.5 megahertz radio telescope.
Little Green Man 1
By 1967 the radio telescope was generating reams of data; Bell was responsible for analysing more than 700 metres of print outs a week. One evening, she noticed a few unusual signals which she termed ‘scruff. These ‘bits of scruff’ seemed to indicate radio signals that were both too fast and too regular to come from quasars.
Initially Hewish was dismissive of her discovery, believing the signals were man-made; she had to be persistent in reporting the anomaly. Finally Hewish worked with her to eliminate the possibility they were from orbiting satellites, TV signals or radar. They jokingly named the discovery L.G.M. 1 – Little Green Man 1.
Just before Christmas, Bell noted a second signal in another part of the sky; a few weeks later she found two more. All pulsed regularly. Looking at papers on theoretical physics going back to the 1930s, Bell and Hewlish realised that these signals must have emerged from collapsed stars. When a star runs out of energy, its outer layers explode in a supernova and its centre collapses. If the original mass of the star was around three times the size of our sun, a black hole is formed; if not, the collapse produces neutron stars.
These neutron stars spin rapidly and have strong magnetic fields. They accelerate surrounding electrons into beams of gamma-rays, X-rays, radio waves or light. As a neutron star rotates, the beam it emits is only detected when it is facing the earth and so it appears to pulse – in much the same way that a lighthouse beam appears to flash – and so these stars were named pulsars.
A revolution in astrophysics
The discovery of pulsars created a revolution in astrophysics. Pulsars and black holes had been predicted in the 1930s, but had seemed a purely theoretical concept. The detection of pulsars suggested that black holes really existed too – and the first was discovered not long after, in 1971.
As they have such dense mass and precise rotation, pulsars provided a new way to think about space and the theory of relativity, leading to huge advances over the next 50 years, including the detection of exoplanets (planets orbiting other suns) and even gravitational waves.
Nobel Prize exclusion
Hewish and Bell published their findings, with Bell’s name second out of five scientists listed on the paper. In 1974, Antony Hewish was awarded the Nobel Prize along with Martin Ryle for pioneering work in astrophysics – Hewish for his ‘decisive role in discovering pulsars’ and Ryle for his work on radio telescopes. Bell’s name was not mentioned. A number of notable scientists protested, but she said, ‘It would demean Nobel Prizes if they were awarded to research students.’ However, Bell admits that her gender may well have had an impact on the decision and has spoken of meetings between Hewish and Ryle to which she was not invited.
A woman in science
In 1968 Bell married Martin Burnell and moved around the UK according to the needs of his career, working part time for a number of years after the birth of their son.
Despite this, she studied almost every wave spectrum in astronomy; taught and studied gamma-ray astronomy, including developing and calibrating a 1-10 million electron volt gamma-ray telescope; and studied infrared astronomy in Edinburgh.
‘I’m one of the few women in science,’ Bell Burnell has said. ‘I have pioneered that. One of the things I worry about is what that pioneering has done to me. I have had to fight quite hard most of the way through life.’
She has been a visiting professor at Oxford and Princeton, Professor of Physics for the Open University and in 2008 became the first female President of the Institute of Physics.
In 2018 Bell Burnell was appointed Chancellor of the University of Dundee. Since she spotted that first ‘bit of scruff’ 50 years ago, more than 2,000 pulsars have been found and contributed to the way scientists understand and navigate space – yet there so much more about them still to be learned.