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The importance of pulsars


Physics versus astronomy
Antony Hewish Astronomer
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Pulsars are still a major… will be a very major part of… of the research done by… done by the Square Kilometre Array, and the number of different things that have emerged from the pulsar discovery always give me great pleasure to think that, you know, you were the trigger that… and your work at Cambridge was the trigger that set… set this thing off. The… going back in history, it… it wasn’t long, actually, after the pulsar discovery that I received a letter from a graduate student in the United States – he was called Joe Taylor and he was then a research student looking for something to do and he wrote me a letter saying, do you think it would be a good idea to build an antenna array, something like this, something like yours. And I said, yes, I think… I think that would be a wonderful thing to do, and I gave him a lot of support. But it was Joe Taylor whose research went on from that to bigger instruments using… using major facilities like… like the 1000-feet dish in Arecibo, which led him on to using pulsars for extremely fundamental physics research. And because pulsars are such accurate clocks, they’re immediately useful for testing Einstein’s theory of general relativity. And one of the predictions of Einstein’s theory is that if you wave sufficiently massive objects around sufficiently fast, they generate ripples in spacetime, they distort space and time around them. And… and these distortions in space and time propagate outwards at the speed of light and they’re called gravitational waves, and there’s enormous interest now and enormous amounts of money being spent around the world in various instruments, attempting to detect these distortions of space and time. But the pulsars, because they’re such, they generate… because they generate such intense gravitational fields near them, that they become in themselves physics labs for… for testing general relativity. And Joe Taylor, who was a graduate student, when he, when he first wrote to me and got interested in pulsars, was finally awarded the Nobel Prize for… for demonstrating that gravitational waves must exist. In 1975 he discovered a pulsar which was in orbit about a neutron star, it became known as the first binary pulsar. And the orbit of this… of these neutron stars is extremely rapid: they orbit each other in just over 7 hours, which is… which is an incredibly close and rapid orbit, and they’re… they’re generators of gravitational waves. And Joe Taylor was able to demonstrate from careful timing of his pulsar that, over the years, the… the orbit was shrinking as orbits must if they lose energy, and it was shrinking at exactly the rate you would predict using Einstein’s theory of gravitational radiation. So that Joe Taylor… well, I… it was Taylor and Hulse – his graduate student, Hulse, who discovered this pulsar, but it was Joe Taylor who actually used it to check gravitational theory. Over… over many years observations they found that the approach of the neutron stars was at exactly the right rate to be explained by energy loss into gravitational waves. You couldn’t detect the waves directly as distortions of space in time, but you could detect the energy loss in them, and that fitted Gravitational Wave Theory precisely to within a fraction of a percent. And Joe Taylor was awarded the… the Nobel Prize for that. Now, the Square Kilometre Array, when it exists, is going to follow up all sorts of different kinds of physics. At the moment we know something like… we have discovered about 2000 radio pulsars, radio emitting pulsars, in our galaxy and with the Square Kilometre Array many, many more are going to be discovered.

Antony Hewish (1924-2021) was a pioneer of radio astronomy known for his study of intergalactic weather patterns and his development of giant telescopes. He was awarded the Nobel Prize for Physics in 1974, together with fellow radio-astronomer Sir Martin Ryle, for his decisive role in the groundbreaking discovery of pulsars. He also received the Eddington Medal of the Royal Astronomical Society in 1969.

Listeners: Dave Green

Dave Green is a radio astronomer at the Cavendish Laboratory in Cambridge. As an undergraduate at Cambridge his first university physics lecture course was given by Professor Hewish. Subsequently he completed his PhD at the Cavendish Laboratory when Professor Hewish was head of the radio astronomy group, and after postdoctoral research in Canada he returned to the Cavendish, where he is now a Senior Lecturer. He is a Teaching Fellow at Churchill College. His research interests include supernova remnants and the extended remains of supernova explosions.

Duration: 4 minutes, 35 seconds

Date story recorded: August 2008

Date story went live: 25 June 2009