The woman who discovered pulsars:
Jocelyn Bell was a graduate student mapping twinkling quasars
under the direction of Tony Hewish in 1967 when she came upon
unusually regular radio waves. The precision of the waves being
so perfect, she thought that it must be interference of some sort,
or perhaps extraterrestrial life signalling from a far off planet.
At first, she jokingly labelled them LGM's (Little Green Men).
Then a few months later she discovered another, LGM 2, and knew that,
indeed, it couldn't be extraterrestrial life nor interference -- both
were too unique in their identities. In February 1968 Hewish and Bell
published an article in Nature magazine that discussed these
findings. Jocelyn Bell, under the direction of Tony Hewish, had
discovered the first pulsar. In 1974 Tony Hewish received the
Nobel Prize in Physics for this discovery.
A bit about pulsars. Pulsars are strongly magnetized neutron stars that contain phenomenal amounts of energy. They have a shell, analogous to an egg (except pulsars are the most perfectly round thing ever found), made up of iron that is 10 times denser than iron found on earth. Inside this shell is a superfluid. These tremendous little power sources have the unique characteristic of emitting radio waves that have periods of milliseconds to several seconds. They emit beacons of light like that of a lighthouse within these regular intervals. They spin incredibly fast, so fast in fact that the energy produced from this revolution can produce a thousand million volts. Their density is so great that a teaspoonful of material from a neutron star would weigh 100 million tons (the average size of a pulsar is about the size of the city of Albuquerque).
Jocelyn Bell has pursued many endeavors over the past thirty years. I had the distinct pleasure of speaking with her while she was in Socorro to receive the Jansky Award. I met with her at National Radio Astronomy Observatory with NRAO Public Information Officer, David G. Finley. I was delighted to see that she was quite a gentle woman with a lyrical Irish-Scottish brogue. She was extremely modest, admitting that the discovery of the pulsar had a lot to do with luck. The following are excerpts from our discussion.
KMW: You wrote an article in 1992 entitled, "A Quarter of a Century of Surprises." Can you tell me about that? BELL: It was 'round the bout twenty-fifth anniversary of the discovery of pulsars. It was a fairly short piece, just reflecting on the last twenty-five years. The main point of it was that often when a science subject is twenty-five years old, it's beginning to settle and it's becoming mature. Oh, it's still good stuff, but it hasn't got quite the same punch to it the way a very new subject has. The pulsar field for some curious reason has stayed very dynamic. Staggering things still come rolling in. In a sense that's one of the surprises about the field: that there still are surprises. The article was mainly on that sort of line. The kinds of surprises that there've been have been -- the discovery of the very fast millisecond pulsars, the things that are going several hundred times a second, which we wouldn't have believed possible if we hadn't seen them yet. The discovery of planets around pulsars is utterly staggering. There are three very good reasons why there can't be planets around pulsars, yet there are. To some extent the supernova in February 1987 in the Magellanic cloud in the nearby galaxy checked out all our theories of astrophysics beautifully, including evidence of the formation of a neutron star, or pulsar. But following the evidence for the formation there has been no subsequent sign of it. That's a puzzle. There may be black holes rather than green anything. So there's a field that's still very dynamic and very exciting with a lot of fun things happening. KMW: Are you still working in pulsars or you onto other endeavors? BELL: I'm working in neutron stars of which pulsars are perhaps a major set in a slightly larger beat. So the kinds of things I'm interested in you can detect in radio waves as pulsars, you can detect in x-ray wavelengths as one of a pair of stars, you can detect in gamma-rays, maybe even some of these gamma-ray bursts, or you can look at different aspects of all these different things in the spectrum. And the bit that I'm particularly working on at the moment tends to be towards the middle of the spectrum, the very short wave radio, the infrared and studying objects there. KMW: Did you always want to become an astronomer? BELL: Certainly from my teens, yes, but before that I wasn't quite sure what I wanted to be. I became interested through reading my father's library books. My father was an architect, but a very wide-ranging brain. In Britain there used to be a competition on the radio, a quiz program on the radio called "Brain of Britain," and he was one of the finalists or semi-finalists in one or two years of that. He was very broadly intelligent and bought all sorts of books. I think I probably had a quick look at most of them, but it was the astronomy ones that actually got my attention. KMW: What types of courses did you take at Cambridge and before that inspired you? BELL: I had a very good physics teacher at secondary school, when I was between fifteen and eighteen. He was distinctly elderly, he'd come out of retirement for a second time to teach us, and we had very, very little equipment in the school. It was a girls' boarding school in England,a Quaker girls' boarding school. And certainly in Britain, girls' boarding schools had difficulty getting good science staff. So we were very, very lucky in this physics teacher who was very good and with a subject like physics once you understand it it's that easy. It's the one, I think, that involves the least learning. You don't have to learn lots and lots and lots of facts; you just learn a few key things, and if you really got hold on them, then you can apply and build and develop from those. So I think it appeals to brains with rather few cells. He was a really good teacher and showed me, actually, how easy physics was, and I think that was the key. Otherwise I must have gone some other way. KMW: The Open University has an enrollment of between 150,000 and 200,000 students. How do you reach, how do you teach that many people? BELL: Well, right now we've just had our exams, and I am supposed to be coordinating the marking of 1,000 astronomy scripts [tests]. We've got a thousand students all over England, Scotland, Wales, Ireland, and some other bits of Europe. These are all mature students, typically 30's maybe early 40's. A lot of them are people who left school quite early having been told by their school teacher that they were "thick," and they believed that school teacher for awhile and then they began to wonder and began to think "maybe I'm not so thick." They begin by taking evening classes, get interested in studying and decide to have a go at getting a degree. They're doing it by distance learning. They get a lot of stuff through the mail. The postman brings them great big packages full of study materials, kits for doing experiments at home with, video tapes. A certain amount of stuff is broadcast over the television network, radio programs, things like that. They do it nearly all at home and nearly all by themselves, but they have a local tutor. For instance, if we were doing it here in New Mexico, there might be somebody in Albuquerque and there might be somebody in Socorro and there might be somebody near the border who would be servicing a group of students in their area. If you were having problems with a particular piece, you can write, telephone, or e-mail your tutor and say "look, I'm having problems with this. Can you explain this to me?" There are occasionally face-to-face tutorials, four or five a year. You get sent assignments to do and you send them to your tutor. KMW: How do you grade 1,000 papers? BELL: That is difficult. Last Saturday I called in about a dozen people who agreed to be exam markers. We produce marking schemes in advance. A quarter of these exams are computer marked, where you pencil out boxes and it gets fed into a machine reader, but three-quarters of the exams are marked by human beings, by hand. We quickly learned we couldn't cope with essays, as such. We go for questions that have lots of short parts. The ones that are numerical calculations are very easy to grade. Where you have questions that say "comment on your answer," it's not quite so easy because sometimes they see things that we hadn't envisioned when we drew up the script markers, so markers have to be well qualified and intelligent people who won't use their own initiative. Once we got though the script marking we put all the marks into the computer, and we scale the marks. KMW: What type of astrophysics have you been doing since 1967? BELL: I started in radio astronomy and then immediately I finished my Ph.D. thesis. I moved from Cambridge to the south coast of England because I had a fiancee there and I needed a job near where he would be, so I went into gamma-ray astronomy at the University of Southampton. There were very tough subjects but great fun, very much pioneering work, trying to open up. After about five years there my husband moved, so I moved and I got a job in x-ray astronomy at University College, London, but they were not actually in London. They were in a great big old country house in prime commuter belt outside of London. It had been a mansion and a school, all sorts of things. It was a glorious site. I worked primarily there with British x-ray astronomers on a satellite called Ariel 5. I was in a service role there and I was responsible for the laboratory and it was a huge success. It looks like a golden oldie now, but the discoveries they made....you would just say, "look, satellite, just hold off a bit. I haven't dealt with the last three discoveries." It was terrific. But it's hard work with a satellite because they don't stop. They go round and round and round and they don't take weekends and they don't take vacations. I worked part-time for eighteen years trying to run this satellite. KMW: Do you and Tony Hewish collaborate any more? BELL: Occasionally we have. He stayed in radio astronomy. He's now retired, he's now professor emeritus. He stayed in radio astronomy, whereas I went all around to other kinds of astronomy, so our paths have taken slightly different routes, but I see him quite often. I'm at Cambridge quite a bit, and he's still around and I bump into him and hear about his grandchildren. KMW: What is it like being a woman in the field of astrophysics? BELL: In Britain we only have what you call the full professors; everyone else is what you would call a doctor. And of the full professors in Britain, which is about 150 of them, there are two of them that are women. The womenfolk of my generation definitely carried the load of child rearing and running the house as well. That means you're always working at full stretch. Working part time is a sensible thing when you have small children, but it means you have less time for research. It's also been difficult following my husband around the country. It is significant now we're divorced, and this is the best job I've ever had because, for the first time in my life, I can go for a job because of what it was, not where it was. I don't actually think the way promotions and recruitments are structured that sort of constraint is taken into account. Because the subject is predominately male, inevitably, the standards, the norms are the male. The system doesn't always stop to think, "Has this person had a career break, perchance, or there other constraints? Do we judge them by exactly the same rules as everybody else? In particular, do we use a quantity of achievement as a measure of ability which is awfully easy to do?" This person has a terrific publication record, that one doesn't; therefore, [publish or perish]. KMW: What is left for you in the field? BELL: Maybe no single thing as big as the pulsars, but the fascination of the subject still remains. Astronomy is terrific. There is so much coming in. Keeping up with it all is difficult. DGF: Where did you get the idea of maybe this is a neutron star, because neutron stars were purely theoretical? BELL: And mad theoretical, at that point too. What was happening was initially a very small group of us were working on these curious signals -- Tony Hewish and I, and then gradually, as we devised more tests and things to do, more people got pulled in. For instance, we called in Paul Scott andhis student Collins who had a completely separate radio telescope that worked at the same frequency as ours. So we said, "Now, if their telescope can see that thing as well as ours, then it's not a figment of the imagination of our telescope. It's not that our telescope was malfunctioning, it was something curious. It's not a fault in the telescope or with the receiver. It is beyond that, it's two different telescopes with two different receivers." So we were gradually pulling in more people to help as we thought of more elaborate tests to do.Tony Hewish shared an office with John Baldwin, the radio astronomy John Baldwin, the one that is now the head of the group in Cambridge. John Baldwin had a vaguememory of reading something about very compact objects, remnants of supernovae,something like that, and managed to retrieve the reference. It was he who actuallyset us most directly onto the neutron star path.
It became very clear that these objects had to be very compact, very small because they were pulsing quickly, rapidly. With hindsight we can also see they had to be very massive because they were very good time keepers. So they had big reserves of energy, they could blast out pulsar after pulsar after pulsar and there is no sign of them tiring.
So, gradually it came together, but to be honest I think it was finding the second one that was more like the classic discovery experience. Finding the first one was quite a bit of worry because it was so unexpected, it had to be man-made, there had to be something wrong with the equipment, it had to interference, it had to be satellites in the orbit. With so many things that we had to check out it was really quite a headache,[fearing] that we were spending all these hours checking out something and it would turn out to be utterly mundane and we would have literally wasted that time.
But finding the second one, that justified the point. I found the first four and the Crab Nebula was 6 or 8. The second one, fortunately, came along just about at the point where we were at a sort of impasse with the first one. We got so far and thought, "What do we do now? We have to publish this result very soon. We don't know how to handle it, we don't know what it is." That night we found the second one and, of course, we knew much better what that was. We'd been through all this before. So that was great, that was terrific. Margaret Clark had noticed that very compact radio sources twinkle, scintillate, fluctuate. Tony Hewish had taken up the idea and was exploiting it to pick out the quasars and to map the quasars. The whole telescope array and, indeed, my whole thesis was on the study of twinkling quasars. The pulsars went in the appendix. I've been very lucky and it's been very good fun. It has also been very interesting being forced to work in so many different bits of astronomy. You end up with colleagues all around the country and all around the spectrum, which is very good. It gives you a very wide grasp of things.