Jocelyn Bell Burnell: 50 years since pulsar discovery

19 December 2017

Interview with 

Dame Professor Jocelyn Bell Burnell

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In 1967, a student at Cambridge University came across a series of strange pulsing signals that subsequently went on to transform the world of astronomy. What Jocelyn Bell Burnell had discovered were “pulsars” - small, dense rapidly spinning stars that fire off a lighthouse-like beam of radio waves as they go round. Dame Jocelyn Bell Burnell, as she is now, returned to her old college, that’s Murray Edwards in Cambridge recently to mark 50 years since her discovery by delivering a celebratory lecture. Izzie Clarke went along to listen...

Jocelyn - At that point in time, Cambridge University had one computer. It occupied a room of about this size and it had less memory than your laptop, and that was for the whole university. Our data came out on paper chart, rolls and rolls and rolls of it, because we didn’t have access to the computer. Perhaps just as well… because if we had had access to a computer with limited memory, we would not have programmed it to look for anything unexpected, like pulsars.

Izzie - Have you had many interviews in a room named after yourself?

Jocelyn - No I’ve never, I think, even been in a room named after myself.

Izzie - We’re here celebrating 50 years of your discovery of pulsars, and that was when you were here as a graduate student at the University of Cambridge. What were you initially working on?

Jocelyn - This was in the field of radio astronomy, which was a fairly new young field at that stage and what I was meant to be working on and, in fact, what my thesis was actually on was finding more quasars. Quasi stellar radio sources which are extremely distant and quite puzzling radio emitting objects.

Izzie - It was whilst studying these radio emitting quasars that Jocelyn came across a rather peculiar signal…

Jocelyn - The first thing that came to my attention was that there was a bit of signal that didn’t make sense. I’d got to the stage of recognising the quasars that I was meant to be seeing. I could see - I nicknamed it ‘a bit of scruff’ - there was quarter inch of this funny signal that I couldn’t make sense of in 500 yards, 600 yards, something like that. So it wasn’t very common, it wasn’t very extensive but, because I was being extremely thorough and keen to understand exactly what this new telescope was delivering, I was trying to check out what this was. It finally turned out that this little bit of scruff was a string of pulses, a string of blips about one and a third seconds apart.

...This is what came in on the recorder: blip, blip, missing. Blip, blip, blip, blip blip…

Well, first of all, nothing like that had been seen before, and nobody imagined that anything like that could exist. So it was really really surprising, we had to take quite a bit of time to convince ourselves that it really was a signal from outer space - from stars, and not some weird kind of interference that we hadn’t dreamt of.

For example, I remember wondering if it could be radar signals bouncing off the moon and into our radio telescope. Or could there be a satellite in a funny orbit which mimicked the motion of the stars? It took us several weeks of really hard work; then I found a second one, and a few weeks after that  I found a third and a fourth. So that really does begin to feel like a new kind of star, and then the question is: what on earth… well not on earth… what in the universe could give that kind of signal? What kind of star is this? It’s crazy!

Izzie - This baffling finding was the first detection of a pulsar, also known as a neutron star due to its neutron rich core. But how does a star give off this pulsing signal? Imagine a lighthouse with its two bright rotating beams that can be seen for miles away. Well, pulsars aren’t too dissimilar. This astronomical object spins round with two beams of radiation shooting out from each pole…

Jocelyn - We still don’t fully understand how radio beams are formed but the magnetic field, we’re pretty certain, has something to do with it. And, as this thing spins, if the beam sweeps across the Earth you see a pulse…

It turns out that these objects are small. They’re only about 10 miles across but they also are very very dense, very compact so they’ve got a lot of mass in them. They’ve got a thousand million, million, million, million tons of stuff in a ball 10 miles across. If you take a thimble and squeeze the 7 billion people on Earth into that thimble, then it weighs the same as if it were filled with stuff from one of these stars.

We now believe that it’s the end product, a life after death if you like, of a very big star which has done a catastrophic explosion which has basically killed off the star, dispersed 95% of the stuff out into space. But the 5% in the centre, the core, has been squashed in the explosion and become one of these stars.

Izzie - A nobel prize was awarded but it went to your supervisor. How did you feel at the time?

Jocelyn - I think at the time people expected me to be very angry, but I wasn’t. One of my colleagues, his wife heard the news, phoned him up at work and he came steaming through to my office to tell me and I think he expected to see me explode. I didn’t, because I’m also a political animal. There is no nobel prize in astronomy; there’s not one in mathematics either. Something to do with Professor Nobel and women and other professors, so certain areas he wasn’t going to leave his money to.

This was the first time the physics prize committee had deemed astronomy to have enough physics in it to award the physics prize so it was a huge, huge precedent. I was quite proud it was my stars that had convinced them. I knew that it was going to open the door for other astronomers and a couple of other astronomers have walked through that door subsequently. So yeah, it was very important.

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