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In footnotes or endnotes please cite AIP interviews like this:
Interview of Michael Disney by Mrs. Michael Disney on 1976 February 19,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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An account of the discovery of the Crab Nebula Pulsar by Michael Disney and John Cocke. Meeting Cocke at University of Arizona; international pulsar debate leads to their hunt for the Crab Nebula. Their first observation on an old 36-inch Newtonian telescope at Kitt Peak; trying to find the Southern Proceeding Star; Bob McAllister, Don Taylor and his Multiscalar. Announcement of, and reactions to, the discovery. Comments on events that led to Disney's choice of astronomy; comments on science (equated it with big game hunting) and scientists.
Well, this is the first side of tape number 1. We’re having so much trouble with this tape recorder, you wouldn’t believe it, but we’re in a hurry to get to you in time, to reach you for March the 13th, which means we’re in a hurry. My wife is going to ask the questions, because we don’t know too many English people now that we’re staying in Groningen in the Netherlands. I am going to do my best to answer them. We’ll leave you to do the editing as best you can. I hope it’s OK.
What first interested you in pulsars, Mike?
Well, I think everybody was interested in pulsars in those days, in the astronomical world. It was a seven day wonder, really. Everybody was excited about them, because it was thought that these might be the very first neutron stars, which people had been talking about so long, with exotic properties — notably that they were so dense that the — one cubic centimeter would weigh about a billion tons. AM I was a graduate student in London, and went down to the RAS meeting, that’s the Royal Astronomical Society, meeting in Burlington House in Pickadilly, where the announcement was made by Anthony Hughes, who was the leader of the group that discovered them at Cambridge. And it was a tremendously exciting meeting. You could hardly move there, I think every astronomer in England and a whole lot of people who weren’t were listening to every word, and of course I got excited along with everybody else.
What attracted you to astronomy in the first place?
Well, I was interested in astronomy, mostly from a mathematical point of view. I was always particularly attracted to Einstein’s work, which I read when I was at school. It seemed to me that it was the first time one could really talk about the cosmos as a whole, in terms of general relativity, curved space-time. And — but how I go into astronomy was an incredible fluke, really. I think I should probably get a prize for getting into astronomy by the biggest fluke of all. I was about 25. I had no idea in the world what to do. I had a degree in physics, and I had a serious climbing accident, which laid me up in bed for about a year, and I came across an article in a popular magazine which my father brought home, which, as I now know, was a lot of rubbish really. It was shortly after quasars had it the headlines, and only nine of these things were known. And it was reported that these nine quasars weren’t distributed equally in space.
It seems as if they were particularly associated with our galaxy, which was an incredible result, if true, because they had this colossal red shift, which we normally associate with very large distances and expansion of the whole universe, and here they were supposed to be right next door to us. How could they have a large red shift? Well, there is a way that they could have such a red shift, which has to do with the curvature of space in the vicinity of very dense bodies. And I got all worked up about this, and got so excited about a theory that I developed that I don’t think I got to sleep for about 14 days and nights, just working on this theory, which at the end apparently proved just about everything there was to know about the universe.
Well, after that of course I didn’t know what to do with the theory, having written it all up. And by chance and good luck, (?), an astronomer, I happened to have read one of his books, called to Martin Johnson, of University of Birmingham, and I rang him up, and instead of discouraging me, as most astronomers probably quite rightly would have done, he invited me around for tea. So I went and sat in the back garden with him and his wife served tea under the almond trees, and we discussed this and that, and my theory in particular, and he let me down very gently — because of course it turned out that although it was an ingenious idea, embedded in all of it, I was ignorant of one or two supremely important facts with rendered the whole thing useless. But he did say, why didn’t I go into astronomy as a career? I must say, it’s a thing I’d never thought of, really.
I would have liked to have been an astronomer, but I never thought I could become such an exotic thing. It sounded something like “Why don’t you become a film star?” When I got home, by chance there was a magazine, another scientific magazine lying around, popular one, and I was just skimming through it, till I read it to the end, and there was a position for a graduate student to study star formation at University of London. I said, “Oh, that’s interesting, it’s just nice.” Then I looked at the magazine and found it was nine months out of date. But anyway, in a fit of optimism, I wrote off to them, and in due time I received a polite reply explaining that the job had been filled about seven months ago. And I thought no more of it. Then about five months later on, I’d completely forgotten all about it, to my surprise I received a letter from them, saying that the chap who’d been appointed hadn’t done well enough on his exams, would I like to re-apply? So I went up to London, had an interview. I was accepted. In a few days after I started, I decided this was what I wanted to do the rest of my life, I felt that strongly.
You’d actually started off on a medical career, hadn’t you? first of all?
Among other things, yes.
The idea of looking for the crab pulsar was that, a corollary to your interest in white dwarf pulsars, wasn’t it?
No, it was — why I was in America. I was there officially as a theoretical astrophysicist, but I was determined that whilst I was at an observatory at University of Arizona, a real observatory equipped with real stars, which is virtually impossible in England, I’d try to learn to do some observing. And I was pretty well exhausted by that time with theoretical work. So I t was casting around for a suitable opportunity to observe something interesting. Of course, pulsars came to mind at once.
How did you start setting about looking for the Crab pulsar?
Well, John Cooke was newly arrived at the observatory, as I was, and we were both a bit overawed by all these professional astronomers, rushing up and down mountains and observing the proper stars and talking a whole lot of jargon with which we were unfamiliar. John was a pure theoretical astrophysicist like myself. And we happened to get into two offices next door to one another. We also happened to live sometimes in the same motel with our wives, on opposite sides of the swimming pool. So we got to know one another rather well, and John was I think in much the same situation as I was. He wanted to learn how to do some observing astronomy, but he didn’t really know any more about how to go about it than I did. Anyway, we had a few discussions, and we decided that one thing that was crucial at the time, in the debate about pulsars, was whether or not they were white dwarfs or neutron stars. White dwarfs being a rather less exotic form of dead dense star, many of which were known. So we thought it might be a good idea to see if we could see pulses at night analogous to the radio pulses that were found coming from pulsars, coming from a few well known white dwarf stars. So we applied for some observing time, and there were chokes all around the observatory, to think that two absolutely ignorant theoretical astronomers like ourselves would actually go and observe. It usually causes chokes, I don’t know why. And so we actually applied for time, and I think with tongue in cheek, we were actually granted four nights in January, 1969, to actually look for pulsars. And so we borrowed gear, and we read papers by people about pulsations from various stars, and we, with a little bit of trepidation, not really believing we’d actually ever get to observer properly, that something would intervene in the meantime, essentially put an end to it all, were in a rather desultory way prepared to observe.
The 36 inch telescope was a pretty unlikely thing in fact, to use, wasn’t it, in this particular —?
Yes, the 36 inch telescope, particularly a very old one, which is all the observatory had at the time, wasn’t like a smashing new 90 inch(?) telescope — was all that was available. It was fortunate for us because I’m sure if it had been a bigger telescope, they would have been a good deal less inclined to give us any observing time on it. Anyway, that was what we could use, and that was what we were given four nights on.
The initial research team came from Cambridge, didn’t they?
No. Cambridge discovered four pulsars. This caused an immense amount of excitement. All sorts of astronomers from all over the world were trying to find more of them, and trying to find out more about the ones that were already known. And the original paper on neutron stars, which dates back to 1930, a very brilliant paper by a Swiss and a German astronomer, working in (?) had suggested that neutron stars might be formed in the process of a stellar explosion, when the whole star exploded, and the outside of it formed an expanding mass of gas called a supernova, and the interior, the very center, collapsed to form this extremely exotic object, the neutron star.
So it was suggested that the best place to go and look for some more pulsars was in the vicinity of supernovae. Now, when we set out originally, with our intention of looking at white dwarf stars, shortly after we thought about the project, a very interesting paper arrived from Australia, from a British astronomer out there called Mike Lodge, who had discovered a pulsar which was in the vicinity of a known supernova remnant, in the Southern Hemisphere, which began to wake it look very likely that the original Zwicke-Baade prediction was correct. And if it was correct, that suggested that these pulsars were indeed neutron stars.
So other astronomers began looking at supernova remnants in the Northern Hemisphere, and much the most famous of all these is the supernova of an explosion which took place in 1054 and it’s called the Crab Nebula. Shortly after they began looking, two astronomers at MIT, Reichenstein(?) discovered that in fact there was a pulsar in the vicinity of the Crab Nebula. What was more, it was a very very fast pulsar. The pulses were coming out at a much higher repetition rate, 30 times a second in this case, than any other pulsar that was known, and what was more, the pulses were slowing down very gradually, which suggested that what we had *t the middle of the Crab Nebula was an extremely dense neutron star which was rotating rapidly, and as it rotated emitted pulses of radio radiation. The tremendous energy given off by this rotating object was what was causing the tremendous expansion, accelerating expansion of the Crab Nebula.
How did you propose to look for the pulsar?
Well, we started off saying we would look for white dwarf stars, and then we got this paper from Australia, and then John Cocke went with Ray Wyman to the Relativity Conference, which was held every two years at and at that conference, they heard about this pulsar that had been found near the Crab Nebula, and this very rapid repetition rate, and these things combined made it seem very likely that neutron stars were the sources of the pulsar radiation. And that white dwarfs were not. So the logical thing to do was abandon our white dwarf program, and see if we could find the optical pulsar in the Crab Nebula.
What was the reaction of the other astronomers to this particular project?
Well, I think mostly they thought it was a bit of a joke. After all, here we were, proposing to do a stage of the art(?) observation, in a very exciting branch of astrophysics, with a very old small telescope, and what was more, the two complete duffers to try to carry it out. But there were some very constructive suggestions, and — which turned out to be very useful, in the end. Particularly Ray Wyman, who was the acting director at the time, Professor Brock was away observing in South America, pointed out that if we were taking it seriously, there was a piece of apparatus in the observatory was ideal for the purpose. This is what was called a multiscalar.
If you don’t know what that is, neither did I, but it’s really a miniature computer about the size of a suitcase, with a little screen on it, cathode ray screen, which shows you what’s going on inside the computer. And one of the things you can do with it is to feed the data that comes off the telescope, as it comes off the telescope, into the computer, and it can display it for you, in a useful form; particularly for example it could show us, if we were looking at a particular star, whether the light from it was pulsing. It shows actually 400 little green dots which climb up the screen, and if there’s any pulsation, these little dots form a little wave on the screen. And this apparatus belonged to Don Taylor, whom I’d seen walking about the observatory, looking frightfully busy and also solving irons(?) and transistors and pencil behind his ear and slide rule, and looking very competent and professional, but had very little to do with him, and Ray suggested that we get together with him, his electronics, to carry out the experiment, which turned out to be a very crucial piece of cooperation.
How did you and John get on, first of all?
Well, John and I got along very well because we were two new boys in the observatory.
Holding one another’s hands, virtually.
Yes, we’d only got each other to talk to. Everybody else was so much immensely more professional about all these things than we were, to talk to a Yankee—? We could talk to each other without making pretty much of a filibuster. And Don was, goodness knows what he thought, to begin with. He really must have felt he was involved in something crazy, but sure enough, he agreed to give us three or four days of his time, disassembles all his complicated apparatus, which was intended to do something entirely different, and help us for the course of the experiment. And I think he was pretty impatient at times with about how slow we were and how little we knew. But anyway it all worked out fairly well in the end.
You could have done, quite unwittingly of course, thousands of dollars worth of damage to equipment, couldn’t you?
Well, Don was hovering around it all the time, to make sure that we knew exactly which buttons to press, and which ones not to press.
What’s the very first thing you had to do when you set about a project like this?
Well, in this case, the first thing we had to do was to find where — actually, how to point the telescope and things like that — but more importantly, we had to get a photograph of the Crab Nebula, because it was too faint to see with the telescope with the naked eye; particularly some of the stars in and near it were quite (?). So if we were going to set on these stars, we had to have a photograph of a series of bright stars, which were nearby, and offset, guide off from the bright stars that we could see, and offset the telescope, a predetermined measured amount, to where we want to be. And to do that we had to have an accurate plate, or film if you like, photographic plate of the area, from which we could measure the relative positions of all the stars in the Crab Nebula. So, one night John Cocke and I went up to Kitt Peak, on a night when nobody was using the telescope, because it was mostly a moonlight night. At the beginning of the evening, before the moon rose, we went up to take a photograph of the Crab Nebula, and while we were up there we met Bob McAllister, who was to play an important role in all this. Bob was what they called night assistant, which is rather a misnomer because he’s actually a very strong, silent, knowledgeable guy who lives there with the telescope, and knows every little bit and piece of it and how to make it work. If you need any assistant or advice, how to make things go, Bob knows all about it. He actually showed us how to use the telescope, how to set it up, how to put photographic plates in the developer and so forth. We were real novices at all that, and Bob very patiently showed us how to do this, and we were very proud by the time we finally got a photographic plate, and there it was, in the middle of it, to our surprise really, was the Crab Nebula.
What did you do with the plate?
Well, we took it back to Tucson, and we measured it very carefully with a measuring machine, measured the positions of all the bright stars, and had great big prints made of it about three feet square, with all the stars marked on it, rather like a map, and all their coordinates measured very carefully on it, and the intention was to use this map then to guide the subsequent observations.
If you didn’t know which star exactly was the Crab pulsar, how are you going to find it?
Well, this is where a little bit of detective work comes into it. The (?) Martin’s observations only showed that there was a pulsar somewhere near the Crab Nebula. That was a huge area of sky including thousands of stars. So we had to try and guess which one it was. Well, the obvious place to look of course was right in the center of the Nebula. There were two stars there. One’s called the North Following Star, the other one’s the South Receding Star. Now, the North Following Star had been found in previous investigations, many many years ago by Baade to be an ordinary sort of star which probably had nothing to do with the Crab Nebula at all. It was either in front of or behind, superimposed by chance on the Nebula. But the other star, the South Receding Star, was a very peculiar star, because it had got no — it had a featureless spectrum.
So that was the first place we could start looking. And secondly, a radio source, a very small discrete radio source, had been found many years before by Langevoor(?) long before the discovery of pulsars. (?) found a small source in the center of the Nebula which was in a slightly different position from the South Receding Star. This was a second obvious place to look. Thirdly, a rocket flight some years before had been able to detect X-ray radiation from the Crab Nebula, and the rocket had been sent up just as the moon was passing across the front of the Nebula, and as the moon passes across it, it cuts the X-radiation off, and by noticing exactly how it cuts it off and when it cuts it off, you could tell exactly where the X-rays were coming from. They were coming from a region in the center of the pulsar, in the center of the Nebula, surrounding the pulsar, surrounding the central star, but a good deal larger in size. So what we proposed to do was to look first of all at the South Receding Star, then at Longevoor’s(?) small radio source, and then in the vicinity of this X-ray source.
Do you remember any of the details that took place on that first observing run? What preparations did you make?
Well, I remember it fairly vividly, not so much because we ultimately discovered the Crab Pulsar, that was important, but because it was my first serious piece of observing, and it was for John as well. It was really quite exciting. First of all, we had to get food and so on, because you have to cook for yourself up in the mountain. You live in a little dormitory which is perched right on a ridge overlooking the huge Arizona desert, looking right down to the mountains of Mexico and so on. Then you drive out across the desert into the Papa…(?) Reservation and you go winding up this great mountain, with spectacular views on either side, and of course we’d got all the complicated electronics, at least Don had got all the complicated electronics, in the back of his car. He wasn’t about to let us touch them any more than was necessary. And he took them up in the dome and fitted them all together, all the little bits of computers and the timing gear and photometer output and the graph process and all this, bits and pieces, and showed us exactly how they all worked and we made very detailed notes. And it was all a bit of a rush. For one thing, neither of us really had any idea what it was going to be like. We were very worried about the weather, of course, one always is when one’s observing — was it going to be clear or not? Was the telescope going to work? All the bits and pieces of apparatus, will we get our measurements correctly? And so on. The day before you go observing is usually a tremendous rush, and this was no exception.
Very cold, isn’t it?
Yes, it is, it’s damn cold. Of course, I couldn’t really visualize that it could be cold in Arizona, so I went observing in a thin shirt and sports jacket, and paid the price.
What sort of things do you have to do when you’re observing? What’s the routine?
Well, you usually arrive up to the observatory about 3 o’clock in the afternoon, something like that, and you go up to the — first of all, you go into the telescope there. The dome’s always very cold. They keep it as cold as possible, and close it during the daytime, with reflecting shields on it. This is an old telescope. It’s what’s called a Newtonian telescope. So you actually go up to the top end of it. You have to climb up all those stairs right to the top of the dome, and this is rather frightening, because when you’re up there at night time, every single light is off. There’s not a chink of light anywhere. It’s very easy to fall off the platform and fall about 20 or 30 feet to the floor below, so that’s one thing I think we were all very self conscious about. John and I were. Being near it. And secondly, you have to find out where all the buttons are, so that you can use them in the dark without fumbling. There are many many controls to the telescope. There’s great panels of various sorts of controls. And you want to be able to reach for them in the dark without groping, without falling off the platform, without touching the wrong button.
So we spent quite a bit of time driving the telescope back and forward, learning which buttons to push and so on, how to focus the telescope add so on. Of course we had Don with us the first night, and Don was very familiar with all this, of course. Bob McAlister was going to be with us at all times. He’d be able to show us anything we should have known but didn’t. First of all, we had to ice up the photomultiplier. That’s put dry ice in the photomultiplier to cool them down. This was the — photodetector that was actually going to detect the light, from whatever we were looking at, with. And after we’d done that, and Don checked out all his electronics to see if they were working, — which was rather terrifying to me, there were so many wires and things leading from one place to another one — at the time I thought, all this just simply isn’t going to work. There’s no way we’re going to be able to make sure everything works, at once, which we have to do if we’re going to be successful.
Then we went down to the dormitory, and cooked a meal, which was very pleasant — you sit there with, looking out over the desert, beautiful view, and eat your TV dinner, which is just about standard for the course, have a few glasses of wine. And then of course you’re supposed to put all your warm clothes on, which I haven’t got, neither had John, — just had a large supply of cigarettes to keep me going — and then, all too soon, it got dark. Beautiful night, I remember, lovely clear night. And so that was one main worry out of the way — at least we weren’t going to be clouded out. So about dusk we all trudged up to the telescope, and Don switched all his switches on, and all sorts of little colored lights came on. And John and I began groping about with the telescope. And I think “groping” is just about the right description. For a start, we…
What did you start doing? What were you actually doing?
Well, there were four of us in the dome. There was Don Taylor, who was sitting out with his electronics, and listening I think with a good deal of amusement to what John and I were doing. We insisted on doing the observing, because we thought that if we couldn’t get anything else out of this run, at least we were glad to use the telescope. And Bob McAllister was hovering in the background, giving advice, when called on, and chatting to Don. Of course, it’s very very dark in the dome. We all had torches, and the telescope was more or less pointing straight up in the sky.
You can’t use those torches, of course, can you?
Well, you can’t, naturally, certainly, when you’re actually doing the observation. But when you’re getting the telescope set up and everything else, you can use the torches. The telescope was standing straight up in the sky, and we were tight up at the top of the dome, around the entrance to the telescope, around the place where the light comes into the telescope — the business end of it, where the lens would be on a refracting telescope. Of course this is a reflecting telescope. So your head is pretty well sticking out of the dome. And in fact, when the slit comes down below you, you can see out over the edge of the dome, right out over the desert. And it’s quite frightening really, when you realize there’s almost nothing there. If you fell out of the dome, you’d fall several hundred feet or more down the side of the mountain. John and I were — would be round the telescope. The light comes down there, down what you might call the barrel of the telescope, it’s reflected by the back mirror at the bottom of the telescope, comes up again, and it’s reflected sideways into the photomultiplier and the eye piece, where you actually look through the telescope. It was this photomultiplier, or photometer as we call it, which was connected up to the –- Don’s electronics, which would record the signals and analyze it. But of course at this stage of the proceedings, we were going through the process of trying to set the telescope initially on the South Receding Star, which we see.
So what we were doing is looking through the eye piece, and it’s quite a complicated business. You look through the eye piece, and you see hundreds of little stars, and then you look at your chart, and you try and locate the star field which you see in the eye piece on the chart, just as if it was a map. And then when you think you’ve located a star, which is a matter of practice — it’s fairly simple when you have experience, but when you haven’t had experience, lacked it, as we did, it becomes quite a business. When you find some stars though, a little pattern of stars which you think you can recognize, you then drive the telescope and you see all the stars skimming past through the eye piece, looking for the other stars you think you should find. Of course this took us a bit of time, and when we located the actual star we wanted, one of the stars we measured, as being near the Crab Nebula, we then started doing very careful micrometer measurements.
The eye piece is fitted to screws, which have got micrometer readings, and by moving the micrometer, and then moving the telescope, you can move the telescope an absolutely measured distance from the stars. Now, this in fact took us all the first night. I’d be — John would be looking through the eye piece, pressing the buttons, say, and then saying, “Right, we’re on star number so and so, and the micrometer readings are XYZ” or whatever it was. And I’d be writing it down on a piece of paper, and then using my slide rule to calculate how far away we were from the Crab Nebula and how far we had to move. It all sounds very dull. But you have to understand that this sort of observation, with so much effort going into it and so much depending on it, it is absolutely essential that we were certain that we were on the right piece of sky, because essentially with a small telescope like that, all we’d be looking at would be a very tiny portion of black visible sky with nothing in it, and the whole exercise would have been futile if we hadn’t been sure that we were on the right place. So we checked and we double checked, and Don — we could hear Don muttering in the background. I’m quite sure he would have set the telescope up a good deal quicker than we did.
Anyway, we — it was important, if we were to feel that there was anything worthwhile coming out of this experiment, and even a negative result would have been interesting, that we were actually looking at exactly the right spot. Well, the whole evening passed. We took one reading and then we took another one. We hadn’t appreciated how difficult it is actually working in the dark, and in these days modern telescopes have computers which interact with the telescope controls to do these things for you. But as I know now from a good deal more experience, it’s very easy to make simple mistakes on this sort of — in this sort of work. Technique. And of course, we were doubly worried because people had told us that the telescope offset guide that we were using, to offset the telescope from a given star, was unreliable. Anyway, the Crab Nebula began to set, got lower and lower in the sky, and we were still measuring stars when we had to call off the night’s observations, having done absolutely nothing useful whatever.
Well, the next day, I think Don went down to Tucson to get on with his work. When we woke up in the afternoon, John and I checked all the observations we’d made the previous night, and to our surprise, everything seemed to check out. So it looked as if the offset guider was going to work, and that the whole observation was going to be feasible. So we went for a walk around the mountain in the afternoon, and — they have lots of telescopes up there, you know, about ten or fifteen telescopes. So it was quite interesting to walk around and see what everybody else was doing, astronomers in all the domes, getting their equipment ready for the following night’s observations. And after dinner, Don came back up again, and we got going once more. This time, we were reasonably sure that we’d set the telescope on the South Receding Star, which we felt was the most likely candidate. Then we could start taking observations. This is when things got more interesting. Don showed us all the apparatus.
Naturally, if you ignore all the wires and things, that disappear from power supplies and counters and everything else, the actual apparatus, if you just understand its functional purpose, is quite simple. It was a very elaborate time device which we had to set to the known period of the pulsar, which had been determined to about 8 or 10 significant figures by radio observations. We had to set this period exactly into a counter oscillator, which essentially counted oscillations. You dial this number in. This thing gives off timing pulses at exactly the same time, with exactly the same period as the pulsar has. And there’s one important thing which one should return to later on, and that is, we had to adjust our period, because in the earth’s orbit round the sun, the period of the (?), the apparent period of the pulsar would be changing. So we had to make corrections — the measured period each night, in order for us to be on the correct period for the pulsar. And this turned out to cause us some trouble later on.
Anyway, Don showed us what happened, how it all worked. The photomultiplier counts photons arriving from the tiny little whole which is the only better thing(?), a photometer, which is letting light in. You can imagine this hole projected on the sky, covering the region, small region round the South Receding Star, and all the light from that region — I say all the light, there’d be very very little light really, there might be, oh, I don’t know, something in the region of a hundred photons per second — would come into the photomultiplier, where it would turn into electrical pulses. Don had fixed up a rather neat little device which was a microphone on his output from the photomultiplier, tube, so that you could hear the photons coming in like “click click click — click click — click click click click” at a rate of about 100 a second.
So we knew that the photomultiplier was working. And then these photons then came into the computer, or the CAT as it was known, Computer of Average Transience, and also into the computer came the timing signal from the period generator, and this — the computer divided up the signal into 400 channels, each channel covering 1/400 of the phase of the pulsar, so every — the pulsar pulses every 33 miniseconds or 30 times a second. So all it does is, it takes the (?), all the signal from a 33rd of a second, no, a 30th of a second, and it divides it up into the 400 channels, and it goes back to the next 30th of a second, and puts the next 30th of a second signal on top of the previous one and so on. So every 30 times a second, it divides up the signal, and lays it on top of each other in the computer memory. And what we saw on the screen then would be 400 little green dots and each dot, the height of each dot denoted how many photons had arrived in this particular part of the pulsar’s cycle. And what we were looking for was for a pulse to appear amongst these little green dots. Instead of being a straggly little line of green dots looking very much like grass, you are looking for a pulse to appear amongst the green dots, a definite rise somewhere along the line of the green dots.
Well, we watched in fascination as we sighted the very first serious run, and absolutely nothing happened. There were lots of places where some of the green dots got out of line temporarily, and we all looked at it hoping it would grow, and it all evened out again. But I won’t say we were disappointed, because I don’t think any of us really had any profound conviction we were going to find anything. We simply didn’t find any pulse whatsoever from the South Receding Star. The remainder of the night, we put in different colored filters, which would look at different sorts of light from the South Receding Star. The ultraviolet light. Because it might have been true that the pulsar was only pulsing in a particular color. There was no pulse in the yellow. There was no pulse in the blue. There was no pulse in the ultraviolet. So the next thing was to try to search the other areas of the Nebula where we thought the pulsar might be. That was the (?) radius star, and we didn’t get any luck there, and then we looked at the X-ray area. Divided it up into squares to search. Altogether it took us most of the night to, that first, or second series of observing nights, to show that really we weren’t getting any pulses whatever.
Don showed John and I how to use the electronics. It was really very simple. I should say a word here about the other system that we ha for recording data. In case anything went wrong with the computer, we were at the same time recording the timing signal and the incoming photon pulses on a two channel tape recorder, and since we had massive data on this tape recorder, with all the photon pulses, all the timing pulses, all the different runs, all the different filters, different places in the Crab Nebula, we were recording comments between all these runs, with an ordinary microphone so that later on when we sorted out the data down in the laboratory, we would be able to tell which data went with which particular observations. So that we had a microphone which had to be where we were putting comments, had to be plugged into the tape recorder, — we’d make our comments, and we’d pull the microphone out, and then only the signal was going on the tape. And most of the time, Bob McAllister was working the electronics, and he found it was jolly difficult to pull the socket out and then put it back in again, in the pitch dark. So as it happened, during the run when we were recording the photon pulses, he’d leave the plug in from the microphone, loosely in its socket, and as we found out later on, as well as the data being recorded on the tape recorder, all the, everything that was going on in the dome was being recorded by, all the voices were being recorded on top of the tape as well. And that’s the tape you have a copy of.
Well, the net result of the second night’s observations, we didn’t find the pulsar; I think Don got fed up with the whole thing and John Cocke and I had learned anyway how to operate all the electronics and the telescope and everything else. So he left us the next morning and went down the mountain. That left us with two more nights. And we were really discouraged, we didn’t know what to do. Anyway, we thought we’d have another go if we could. Well, actually what happened was, the clouds came in, and so though we stayed up there for two further nights, we didn’t do anything are of useful observation at all. And we were just preparing to disassemble all the electronics and take it down the mountain, when we had a telephone call from Bill Tift who was going to observe on the telescope after us, saying that his wife was sick and he wouldn’t be able to observe, that if we liked we could have the next two nights of observation as well. So we said, “Oh well, OK, that would be very nice.” We’d at least repeat the experiment again, to make absolutely sure then wasn’t a pulsar. I went down the mountain as well.
I went to attend a couple of lectures at the university, and I came up, the first one of our extra nights, late in the evening, just in time for dinner. It was still cloudy, but I could see the clouds clearing up, and there was just a single cloud close around the very topmost rampart of Kitt Peak. It’s rather funny, I can’t help but remember, as I was driving towards it in the desert, thinking, “Looks like a sort of good omen, to see the clouds all clearing away just at the last minute.” We went up there. John was seated at a table in the dormitory, with a page of figures in his hand, and he told me that he’d discovered a mistake in the corrections that he’d been making to the timing period, that I referred to earlier on. At least he thought he’d made a mistake, so we went over the calculations, all over again, and it’s what had happened. We calculated the correction that we had to make to the actual pulsar period, but we got the sign wrong. So that explained then that all our previous observations were virtually worthless as which was quite exciting, because it meant that we could start again from scratch, and it might be that the pulsar was still there. So immediately after dinner, Bob McAllister, John Cocke and I went back up to the telescope, as Bob was working the tape recorder, and I think I was setting the telescope, and John Cocke was rearranging the timing.
We set on the South Receding Star in exactly the same way as we had before. We were surprised to see all the electronics were working, although Don Taylor wasn’t there, and we, without any great expectations of finding anything, we started on the first run. We all crouched in front of the telescope. It was running itself by then. We all crouched in front of the tiny little screen which is about 10 centimeters across, watching the green dots climbing up the screen. On the very first run, a pulse began to appear in the middle of the screen. And I can’t, I shall never forget that, because it was right in the middle of the screen, which seems rather unlikely in the first place. I can remember being absolutely breathless with excitement, and shouting out, “My God, there’s a bleeding pulse out there?” John was swearing to himself and saying, “Christ on a crutch!” So, there it is — we looked at it and looked at it. We didn’t want to believe it. Then we discontinued the observation. We just all three of us stared at this line of dots on the screen with a definite pulse right in the middle. And of course that’s what really worried us, because the pulse could have appeared anywhere.
It was rather unlikely that it could appear in the middle. It seemed as if it might be an artifact of the electronics. So we talked about this a little bit. And then we said, “Well, let’s repeat the experiment,” so we recorded the first pulse on the graph plotter, so we’d have a definite record, an indelible recording of it, and I think we were all pretty silent and not really knowing what to believe. We set the thing up again, re-set the telescope, re-set the timing, and away we went. Once again the pulse appeared, but this time it appeared slightly off center on the screen, which was very exciting, because it meant that what had worried us the first time wasn’t a worry at all. I think we went hysterical with excitement. Well, I can remember that I was hysterical with excitement. I really felt we’d found the pulsar. John was a good deal calmer and more scientific about it. I don’t know what Bob thought. Taking it in his usual laconic way. But every now and again we’d stop, for all sorts of tests that we could carry on about the pulsar, and if in either case we picked up pulses again, then of course there was something seriously wrong.
It was probably an artifact. I think the first thing we did was to move the telescope a little bit off the South Receding Star, so we wouldn’t be getting it in the diaphragm. Then we switched everything on, and we sat with bated breath in front of the screen, and I can remember my heart jumping through the floor because there was the pulse once again. It seemed as if it was an artifact. We did the observation and stopped and recorded the pulse, and then we started talking about it, and we realized then that we hadn’t actually moved the diaphragm completely off the pulsar. The pulsar as right on the edge of the diaphragm, so that we were probably getting some pulse light anyway from the pulsar. So the next run, we moved completely off the pulsar, well and truly clear, and sure enough, there was no pulse. So the next thing that we decided to do, I think it was John’s idea, was to move back onto the pulse, and change the timing period so that it was different from the pulsar period. Once again we got a negative result, which was reassuring. Then the real crunch came, when we put the thing back on the pulsar, put the timing right, — and there was the pulse. And that was when we really believed it. I think we really all went mad with excitement.
I think even Bob McAllister was getting excited then. I think — one thing, I felt very bad that Don Taylor wasn’t there, and immediately rushed downstairs and telephoned him, and said, “Don, we’ve found the pulsar!” Don was at home, and I could hear him sort of thinking things over in his mind, wondering about what could possibly have gone wrong. There was one thing that worried us all, which was that the pulsar period, which is roughly 30 cycles a second, is very close to the mains frequency of 60 cycles a second, half of it, so there’s all sorts of electronics artifacts which can get in through the mains, which could manifest itself as a pulse. Anyway, he suggested several tests, and I could see him torn between enthusiasm on the one hand, and skepticism on the other, and he suggested one or two things we could do. So we went back to the telescope and did them. And sure enough, the pulsar behaved exactly as a pulsar should. It didn’t appear where it shouldn’t appear, and it did appear when it should appear. And so the next thing we did was to ring up our wives. And as it happened, you were having supper together, weren’t you?
That’s right, they were having supper together at Clare’s house, that’s Clare Cocke’s house. My wife and Clare were sitting there together, and I rang up from downstairs, there’s a telephone in the dome, and said, “We’ve found the pulsar!” I don’t know what happened next. What did happen?
I think I said, “Tell Ray Wyman.”
Yes, and I was in such a state of excitement that I rang up Ray, and sort of shouted down the telephone, “They’ve found a quasar!” With Clare nudging at me at the side (whisper) — “A pulsar! A pulsar, you idiot!” Of course Ray took it all so very quietly. Said we should take it easy, and don’t say anything to anybody until he’d had a word with you.
Then you went out and celebrated, didn’t you?
Yes. Not exactly then though because we wanted to wait until we had a little bit more. And then afterwards we had a second call. I think it was John this time talking to Clare. And Clare said, “Go out and get some food.” I don’t know what we’d been eating up to that time. I went rushing out to the supermarket, which is open 24 hours a day in the district, and was so full of it, I had to pull in and get petrol, and I was sort of jabbering about this thing to the petrol attendant. And I got to the supermarket, and was jabbering once again to the young man who was serving at the desk, and as it happened, he was a science student, doing some late night work to help him through college, and of course he was quite fascinated, but didn’t really believe, I don’t think, what he heard.
This is the second side of tape number 2. Yes, so, there we were, with this tiny screen, I’d say about 10 centimeters across, four heads — Yes, well, there was no pulse to speak of the first time. Oh, it was pretty depressing. We couldn’t think what was happening. Pulled out all the wires and pushed them back in again, turned all the switches back and forwards, re-set the telescope, and I really don’t know what happened, looking back on it, but for some reason or other the pulsar seemed to be in our apparatus very weak that night. Anyway, it did finally come through. We could see the pulse. Don was convinced. We believed that the thing must be variable. After all, that wouldn’t be surprising at all. Radio pulsars were extremely variable. You could sometimes see them very strongly, and then they’d disappear altogether for weeks at a time.
So, the fact is that it did come back, and we were all very excited this time. I don’t, I can’t remember all the things we did that night, but what we were trying to do more than anything else was to determine exactly the position of the pulsar, so, to do that, what we had to do was essentially drift this tiny diaphragm about in the sky until the pulse disappeared from the screen. By finding out exactly when it disappeared, we could locate exactly when it was. That was a very time-consuming job. It took us all that night, and I remember when the Crab set, which was I suppose, I don’t know, about three or four o’clock in the morning. We all traipsed down to the library, and the dormitory with all our stuff, and we had a few beers, and a great amount of tobacco, all feeling very charged and elated, and trying to keep sufficiently cool heads to calculate this position correctly, which we did. Then we were debating how to do it, because we were worried, amongst other things, I think this is a perennial worry amongst scientists working in a hot field, that we might get scooped.
So we decided that the best thing to do was to send off a telegram to the International Astronomical Union, which receives telegrams on important observations, and sends copies of these telegrams around to every important observatory around the world, the idea being that astronomers can keep in touch with one another and if anything interesting comes along, like a comet or an outburst of a supernova or anything, everybody can switch on their telescopes at once and no time’s wasted. So about 4 or 5 o’clock that morning, we put a telephone call through to the telegram service and sent off a very terse telegram saying that we’d found the pulsar in the Crab Nebula, giving its strength, that was the other thing we measured, and the period, and most importantly the position. Then we all went off to bed. So the next day, Bill Titt(?) came up. He very kindly said, “Well, gosh, you guys are doing something important, you carry on.” But what was really worrying us was that we couldn’t eliminate the possibility — here we had these two stars in the middle of the Nebula, very close to one another, we couldn’t eliminate one or the other.
We weren’t sure which one it was. And to be sure which one it was we really needed a telescope with a larger scale, not so much one that would collect more light but which had a, if you like, a larger magnification, so that we could put a very small diaphragm on one star, and then on the other one, and we could get it determined straight away very simply which one was the pulsar. We knew it had to be one of the two, because the strength of the signal was such that the object emitting it would have to appear as a fairly strong star somewhere in the middle of the Nebula. So we decided that we’d walk along the mountain in the afternoon, and there is, there was in those days, one other large telescope, much larger than ours, the 84 inch, at Kitt Peak, National Observatory, to see who was on the telescope, and ask if we might bolt our equipment on the back end of the telescope for half an hour, just to determine this very, to discriminate this very important point as to which star it was, and to get a single very good pulse from the thing to exactly what the pulse shape was, compare it to the radio, and to see, it might tell us something about the emission mechanism and so on.
So about 5 in the afternoon, we went over to the 84 inch telescope, and the observer who was on at the time was down in the observer’s bedroom, and we talked to him and asked him about this possibility. And he wasn’t very enthusiastic at all. He took the professionally correct, but I think very cold blooded attitude that after all, it was his night to observe and he was going to observe. So we went back to the 36 inch, and we realized now that having sent this telegram off, there would be a lot of other people working on the pulsar, and indeed it turned out that the people at Kitt Peak National Observatory itself on the very same mountain were going to work on it the following night, too. There was a lot of interesting stuff to be done, and we weren’t sure really how we were going to do any of it, because we didn’t have the right telescope. The first thing we tried to do was, we fitted a little bit of polaroid which we found somewhere, polaroid material, to try and work out the polarization, which was also very important, and the colors of the pulsar.
We got the colors all right, but we o the polarization, we didn’t really hate enough signal. It wasn’t a big enough telescope to measure the polarization. That was something we spent a lot of time doing later on with the large telescope. But the important thing to start off with was to find out which of these two stars was the pulsar, and we talked about it at dinner, and that night it was pretty cloudy. We did a little bit of work but not very much. We came to the conclusion that the only thing to do was to make a smaller diaphragm, a very small square diaphragm about 1/10 of a millimeter square. It would have to be pretty exact in shape and size. So the question was, how we were going to do that, and we had to do it before the next evening. So I remember we spent the whole day with some kitchen tinfoil from the kitchen, trying to make a tiny little hole in this thing 1/10 of a millimeter square.
We finally succeeded in doing this, to everyone’s amazement. We had a — I can remember all four of us working on it, John, Don, Bob McAllister and myself, and we had a microscope which we’d found somewhere in the building, and we were working looking through the microscope on this tiny piece of kitchen tinfoil, with pairs of tweezers and razor blades and so on, and when the guy who was making the actual cuts, I think John was the actually doing the brain surgery, everybody held their breath tight after he drew a line, cut a line in his tinfoil. But anyway, round about 5 o’clock, we finally had a diaphragm, which we gingerly placed into the telescope. And by this time, we’d had several phone calls from people, either congratulating us or asking questions about it. We had a pretty shrewd idea that several big telescopes would be working on the pulsar that night, and were rather determined to see if we couldn’t make the first, identify which of these two stars it was ourselves. We were in a big rush because we knew that everybody else would be working on this and they’d presumably be sending out telegrams, because it was pretty important.
As soon as it got dark, we set everything else, and Don Taylor had a clever idea. In order to find the pulsar exactly, to do it by ear, which was listening to his photometer. He could push it, the telescope, guide the telescope across the center of the quadrant(?), and when it got to one of the two stars, we’d hear the photomultiplier going “brrrrrrrrr” and then it would go “brrrrr” — and so this is what we did, and Don would be sitting there with his ear against the microscope while John and I were watching the screen, and he’d drive it about blindly, and when it got in the right position, with this very very tiny diaphragm, until suddenly, “Brrrrrr” and we’d watch the screen to see if it was a pulsing source as well. And just about half past 8, 9 o’clock, we finally picked up one of the stars with a pulse. We were pretty sure it was the South Receding Star, because when we drove it off to the north and picked up the other, we could hear the other star when we drove off to the north and it wasn’t pulsing. Just at that moment we had a telegram call from the wife of the other astronomer at Kitt Peak, who was now working quite avidly, saying that they had established that it was the South Receding Star, as well. I think that really covers most of the observation. We continued observing for another couple of nights, but —
About Clare and myself?
Oh yes, that’s right. There was pandemonium up on the mountain because Clare and Inge, that’s my wife, insisted on coming up the mountain. I don’t think anything had been seen like it. We were having great big dinner parties with lots of wine and everything else, and then going up to observe, and every now and then wives climbing up the stairs and peering between our shoulders to watch the screen, and Inge saying, “Clare, come have a look – there’s a lovely pulse here — hold it, John, hold it Mike —” All very unprofessional. But anyway, it was exciting and I wouldn’t have missed it. I don’t think science should become too solemn. In fact, I think there were a lot of disapproving eyes on the whole situation. Subsequent to that there was a general, what’s the word, a general circular went round to the effect that under no circumstances would wives be taken observing in future.
It was strictly limited to sweethearts, fiancees and mistresses.
That’s right. That’s right… I must say — I’ve never seen any wives observing since. After we’d been on the mountain about ten days, we were all pretty well exhausted I think from the excitement, lack of sleep, one thing and another, and I don’t think we were doing anything useful any longer. So we all packed up, went down the mountain, and as I remember, went to sleep for about two or three days. The hardest thing to do was assemble our wits and our data together and try and write a paper about it all. And it was while we were writing the paper — we decided we’d have to give a colloquium too, and while we were writing the paper and getting the things together for the colloquium, Don had a rather clever idea — playing the original tape back into the CAT, so that people could see the pulse building up in front of them in the colloquium. And he was doing this in his office, with all the electronic gear there, when of course instead of the photon pulses, which of course he did hear, he got our voices coming through, and the whole of that first night, when everything was going on and all the excitement, the whole thing was recorded on tape. And we didn’t even know about it. This was about ten days afterwards. I remember, we had a hell of a laugh after it. We used to go along and listen to it over in John’s office, Don’s office.
So, we got off the paper, and then there was a colloquium, and it was packed out and people came from all over the various astronomical institutes which were in Arizona, and the high point of it was playing this tape over, you know — and hearing us all swearing and blinding(?) and actually seeing the pulse going on the screen at the same time. I think it was rather effective. And then there was quite a lot of publicity. We were interviewed by TIME MAGAZINE. I think it was, and they took photographs of us, which subsequently appeared in the journal. It was also interesting because a number of other observatories immediately, having received the telegram, had gone and observed the pulsar, and thank God had confirmed virtually everything that we’d done, and added some more information as well. One was at University of Texas, and at Kitt Peak itself. They all came over to the colloquium and showed their results as well, so it was really very exciting.
Looking back on it all now, Mike, as a fairly experienced astronomer, what do you feel about it now? Would you do it all over again?
Oh yes. I mean, we were incredibly fortunate, that the first time we went observing, we had a very exciting experience like this. I don’t think there could have been very moments in astronomy when the immediacy of a discovery was so apparent. I mean, there it happened in real time. You know, you were immediately aware of what was happening. There’s usually — I mean, many more important discoveries than this have been made, but usually it’s only after months of careful sifting through the data, and gradual realization of what’s going on, that you understand, you know, the significance of what you’ve done — whereas here, we could see it instantly at the time. And that was very very exciting. It was very exciting to work with other people, I think. It wouldn’t have been half so much — there wouldn’t have been half so much excitement if one had been working on one’s own. Just as much satisfaction but not the same excitement. And of course, it gave us a tremendous big flit(?) in learning to become observation astronomers, and we then had access to other telescopes, to do other experiments in connection with the pulsar, and I think spent the majority of the next two years, John and I did anyway, working on pulsars. But, it’s by no means typical of an average night in the observatory. By now I must have spent literally hundreds of nights observing, I suppose, in Arizona, mostly in Australia, and most of them are very different.
Would you be happy now for instance if Mathias became an astronomer?
I should say that Mathias is our son. Well, I guess it’s a bit like asking yourself whether you’d like one of your children to become a big game hunter. I mean, this is how I see astronomy. I think it’s true of science in general. It’s a form of big game hunting. You go off into some thicket or other, you think there’s something big in there, you’re not sure what it is, and you track it down. It’s a dangerous profession, in the sense that you don’t get — you don’t get your head bitten off, but you, what’s most likely to happen is that one day you find yourself without a job.
And it’s a bit difficult to think about paying bills sometimes when you’re —
It’s a bit difficult to pay them. Well, yes, it is, I think most astronomers would — It is fascinating, but it’s very competitive, and therefore very time consuming. Therefore it really leaves you not very much of yourself to do many other things with. And at the moment, as I say, there’s an awful lot of good guys who, just by misfortune, being in the wrong place at the wrong time, or being in the wrong branch of the subject and so on, are just dropping out, because there simply aren’t enough jobs. There’s three or four or five or six or seven or eight often very brilliant graduate students chasing after one job at a time.
Astronomy is so intellectual, how can you possibly equate it with big game hunting?
Well, I think you can say this — if it was a cerebral, primarily a cerebral activity, then people with first class brains would be the people who were best at science. But I think that’s very far from true. I think most scientists would agree that there’s something more to being a scientist than just having a first class brain. One knows, one comes across very clever people who know an awful lot of things and can do all sorts of things, but they don’t have that pure instinct I think you might call it, I think, that extra urge to follow a problem right into the darkest thicket, and bring it back on a stick, come what may.
I think that’s a very important thing, one has to have. Some people — I mean, it’s very obvious that the way scientists work is so different from each other — it’s more their way of work than their actual intellectual capacity, that seems to distinguish them, at least in my opinion. I think some guys collect data from here and there and so on, work a little bit on this one, then they work a little bit on that one. Others are fanatics about single subjects, devote their whole lifetime, their whole technique to doing one particular thing. But I don’t know, this is my feeling anyway — you’ve got to have this, this, a bit of this killer instinct; that is, you’ve really got to want to find out what the answer is, and push it and push it and push it and push it. And if you don’t have that, then it’s so easy to get the whole problem buried in all the — all the difficulties, or the distractions, all the other things you could be doing. It’s so easy to do teaching or think of a new problem or whatever it is.
If you don’t have this killer instinct, I think you tend to dissipate yourself a lot, and you don’t produce results. I think perhaps the analogy between the things helps to understand why brains by itself is not important. It’s rather like — having a good brain in science is rather like being a dead shot. You may be a first class shot on the shooting range, but it doesn’t mean to say that it’s going to help you all that much when you go hunting in the forest. It helps, but it’s not the most important thing. I think the most important thing, in my opinion at least, and I say this very humbly because — I mean, I think scientists are so different from one another, it’s difficult to generalize. But I think the important thing is to want to get the answer. To really want to get the answer. To really come back with that trophy, as it were. And that’s far more important. You occasionally come across — well, quite frequently, I’d say, you come across scientists where it would appear, you know, that their intellectual capacity is rather limited. But they make up for it by — by this dogged determination, or imagination, or some of the other qualities which are just as important. Here endeth the tape.