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Discovering the first millisecond pulsars
Antony Hewish Astronomer
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Well, as I said, we were pretty lucky ourselves to make that discovery but we were just set up to do it and science is full of discoveries like that, actually. And we carried on: one or two students that I had, graduate students, transferred to do what we could with the antenna and the instruments we've got with pulsars, and we did some good work and… and had some publications for the next 2 or 3 years. But because the large antenna that I had had a huge collecting area and was extremely sensitive, but you couldn't steer it, you couldn't track pulsars across the sky. And if you're going to do the follow-up work, you need something like the Lovell telescope at Jodrell Bank; you must be able to track these things. And so we realised that we'll do what we can and other students hunted the records and we came up in the end with about half a dozen pulsars, six or eight, that we've discovered here in… in Cambridge.

One of the things that we missed, which I was always disappointed about, was the… was the discovery of the first millisecond pulsars, the… the classical pulsars that we were used to, I mean, which led to the discovery, were pulsars which… neutron stars – which are rotating about once a second or several times a second, but not… not faster. But there was one source in… in the plane of the galaxy which we knew was a very strong scintillator and in the plane of the galaxy you wouldn't… wouldn't expect that because things… things would be broadened by intergalactic, by… by interstellar broadening and so on. And there was this 4C source, as… as we called it then, I can't remember what number it was now, but we thought could it be another pulsar because it showed rapid fluctuations when mostly things in the galactic plane don't. And we got… looked for pulsar periods down to… this was Peter Duffett-Smith, actually, doing… my colleague, who was doing this work himself. We chased it down to a periodicity of 10 pulses a second, no, 100 pulses a second, 10 milliseconds, and couldn't… and couldn't see any pulses there, and then handed the data over to Jodrell Bank and said, 'Look, can you do better, this thing looks as though it could be a pulsar but, with our equipment, we can't… we can't track it down to periodicities faster than 100 pulses a second'. And they tracked it down to 2 milliseconds, 500 pulses a second, and said, 'Sorry, we can't see any pulses there, I don't think… this… this must be something else'.

And then eventually, after a number of years, the Americans discovered the first millisecond pulsars, that's to say a neutron star spinning 1000 revolutions, roughly 1000 revolutions per second, actually 600. And that was the first of a new class of pulsar that the… neutrons are spinning as rapidly as that. I mean, it's a fantastic thought that you can make a star as heavy as the Sun spin at 600 revolutions per second, it's just doesn't… it's unbelievable. But that was an American discovery and I was sad that the UK didn't do that, but that was the best the UK could do. And that was a pity. But we did what we could with the antenna and did… did sky surveys and… and found… found the first few, and did some follow-up work, things like features about the pulse shape, drifting sub-pulses and things like that. But ultimately the antenna concentrated on the job it was designed for, which was sky surveys to see which of the thousand radio galaxies had fine structure in them, and that work went on right up until the… the 1990s. My colleague, Peter Duffett-Smith, doubled the size of the antenna; it became the 3.6 hectare array, that's to say about 9 acres, because we'd decided that it was a really good way of doing sky surveys. And… so it was observing, doing what it was designed for, for many years after the discovery of pulsars, which was really just a flash in the pan. And another thing it did… but it was working right up until the 1990s. One of my… one of my interests was still the solar wind.

Born in 1924, Antony Hewish is 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.

Tags: Jodrell Bank

Duration: 5 minutes, 5 seconds

Date story recorded: August 2008

Date story went live: 25 June 2009