Interview with E. Margaret Burbidge
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The interview listed below was conducted as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009), and was transcribed for the NRAO/AUI Archives by TranscribeMe in 2020. The transcript was reviewed and edited/corrected by Ellen N. Bouton and Kenneth I. Kellermann. Places where we are uncertain about what was said are indicated with parentheses and question mark (?).
We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of the original cassette tapes, and for a 2012 grant from American Institute of Physics, Center for the History of Physics, which funded the work of posting these interviews to the Web. Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event.
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Transcribed by TranscribeMe (2020), reviewed and corrected by Ellen N. Bouton and Kenneth I. Kellermann(2020)
Sullivan
So this is talking with Margaret Burbidge on 14th April 1988 at Paris, at the de Vaucouleurs meeting. And can you tell me, when you first came into contact with radio astronomy, what was the first thing that you did?
Burbidge
The first thing was working with my former professor, Clive Gregory, who was director of the University of London Observatory, and I was a junior assistant there. And he was provided with a position by the radio astronomers of a strong radio source, and asked if we could take a photograph of that place where the error box was.
Sullivan
This was Ryle's group that gave it?
Burbidge
This was Ryle's group, yes. And so we had by then, I’d got the 24-inch refractor, which was used for parallax and proper motion work. It had been reassembled after the end of World War II. And it was operating, and we were carrying on parallax observations. And with Clive Gregory's direction, myself assisting, we took a plate of the position of this radio source, and examined it, in the measuring microscope. We didn't see in the error-box anything other than a fairly rich star field. However, we transmitted the data to the radio astronomy group, and we heard nothing more for several months. And then we received a message from the radio astronomy group with a different position, that was not only well outside of the error box of the first position, but was indeed off -
Sullivan
And this was Cygnus A. We haven't said that yet. This was Cygnus A.
Burbidge
Oh, this was Cygnus A. Yes.
Sullivan
Yes, right. And did you take any others? Did you take Cas A perhaps?
Burbidge
No, we only took Cygnus A. We were discouraged by the discrepancy that there appeared to be in radio positions at the time. And Clive Gregory determined to find out why there was this discrepancy. Of course, he'd taught spherical astronomy for decades. The explanation turned out to be that in deriving the positions of radio sources from the lobes provided by the antennae, you needed to know the speed at which the object was transiting across and what had been fed into the calculations by the radio astronomer. They'd not been used to spherical astronomy, had been the solar rate, not the sidereal rate. And this difference, 1 in 365, made -
Sullivan
Made several degrees error difference.
Burbidge
Yes. So we never did take - and we intended to take a picture that might have shown Cygnus A, but we did not.
Sullivan
Then I think you said the Sun was too close to do anything.
Burbidge
Yes, it was months later -
Sullivan
When you got the new position.
Burbidge
Cygnus was no longer there.
Sullivan
So when was the next time you came in to contact with radio astronomy? You and Geoffrey took up a position, well, I guess Geoffrey would be more accurate, took up a position at the Cavendish. In '53 would that be?
Burbidge
Yes, in '53.
Sullivan
And so you must have then had some pretty close contact.
Burbidge
Yes. He was working with the group. They were doing the 3C catalog at the time.
Sullivan
Well, 2C actually.
Burbidge
2C was it then?
Sullivan
The one that had all the problems was being observed at that time but -
Burbidge
They were arguing that the mechanism was plasma oscillations -
Sullivan
That's right.
Burbidge
- from experience with the Sun. And he was on the side of synchrotron radiation.
Sullivan
Now, were you directly involved yourself or -
Burbidge
No. I wasn't involved.
Sullivan
What kind of work were you doing at that time?
Burbidge
I had no paid job at that time. But I had a lot of spectroscopic data from McDonald Observatory on magnetic stars.
Sullivan
I see.
Burbidge
That was measuring and identifying lines and measuring intensities and deriving abundancies.
Sullivan
Right. But were you attending, for instance, seminars that the radio astronomers’ group would have?
Burbidge
Yeah, I would listen to them, but I wasn't -
Sullivan
Right. What was your impression of the group at that time?
Burbidge
A very close-knit group and they would keep things rather secret. In fact, they were doing, at the time, counts of -
Sullivan
That's right.
Burbidge
- what came to be called the log N - log S counts, but they kept their results very secret. Now, they were very opposed to the steady-state cosmology idea, and they were very anxious to disprove this. And the steady-state cosmology predicted a certain fall off of as you go faint, and the log N - log S curve that they derived was a set of three halves, negative three halves, was negative three
Sullivan
Right. Much, much steeper. Yes.
Burbidge
Yes. Much steeper. And so they said, "This is absolute proof against the steady-state theory."
Sullivan
But you knew nothing about this before - you may recall, it was a Halley lecture that Ryle gave in 1955.
Burbidge
That's right. That's right.
Sullivan
Even though you were - Geoffrey was part of the Cavendish and you were closely associated with, but you knew nothing about this until -
Burbidge
Nothing about it.
Sullivan
- until the public announcement?
Burbidge
In fact, I rode up to - it was up to Oxford, wasn't it, where the Halley's lecture was given.
Sullivan
That's right.
Burbidge
I rode in the van with the radio astronomers and they were telling me - at that point, they were telling me -
Sullivan
This is really going to be a good talk there [laughter].
Burbidge
Geoffrey did not come. He was rather irritated by having been kept -
Sullivan
Left out of it. Yeah.
Burbidge
- left out of all the discussions.
Sullivan
Did you go to the thing, this RAS meeting a few weeks later, in which Ryle gave essentially the same talk? I was just wondering if you had any recollections of that meeting.
Burbidge
No, but I do remember meeting - I do remember when it became clear that the radio sources were distributed more or less isotropically. That meant that they had to be something very close to the Sun or something very distant.
Sullivan
Right. This is now probably right back to the '51 or '52 when Ryle was arguing that they were radio stars.
Burbidge
Yes. Yes.
Sullivan
And go on. What were you -
Burbidge
Well, it's part of my recollection is that there was a bitter argument - I think it was - I don't know - held at somewhere in the University of London, the meeting.
Sullivan
Well, this is perhaps the one on Dynamics of Ionized Media that was held at University College in London.
Burbidge
Yeah. It probably was.
Sullivan
That was in '51. Yes. And Gold and Ryle, in the proceedings of this, there are some heated exchanges.
Burbidge
Yes. It was Gold.
Sullivan
You were at that meeting?
Burbidge
Well, listened to it. Yes. Not taking part, but listening. And the Cambridge astronomers' view was that these objects were radio stars. And the possibility was raised, I guess, by Gold and that they might be extragalactic. And this was ridiculed by Ryle colleagues on the grounds that the energies would have to be so large, incredibly large. Yeah, that was -
Sullivan
Yeah. That was 1951.
Burbidge
Therefore, that was before we spent our first two years in the United States. And then came back to the Cavendish and they were accepted by then, so.
Sullivan
But now the first papers that I find in which you actually coauthored - that were relevant to radio astronomy - were to do with some of the famous radio sources. And this in the period of 1955 to ‘60. What was your motivation for doing these? I mean, were you trying to understand the source of the radio emission? Did you want to see why these galaxies were peculiar? How did you get into that?
Burbidge
Yes, because just a radio source by itself is not much good unless you have an optical observation to go along with it. And to get a distance, you need to know redshift. And so the idea was to take what identifications - they were coming out, some better identifications and reasonable positions, and some nearer galaxies that had been identified. And we wanted to find out what it was that was peculiar about these galaxies. And Geoffrey was also working out the energies. And the energies required both in the particles, high energy particles and in the magnetic field and the fact that the minimum energy conditions when you had equal partition into two modes. And you had to consider whether you had only electrons to provide the particle energies or whether there was a component of protons.
Sullivan
On the synchrotron hypothesis.
Burbidge
On the synchrotron. Yes. So this was really his work, and I was just a partner in that. Let's see. When was it we took our first observations of radio galaxies? I guess it was after-- we got involved, of course, in the synthesis of the elements. And that took the whole second year that we spent in Cambridge, working mainly with Willy Fowler and Fred Hoyle. And our involvement in that started really through the spectra that I had been analyzing about the peculiar abundances in magnetic stars. And we needed to find out something about neutron capture processes. We didn't know very much. And we went to Fowler for help. And that started the whole of the collaboration going between the four of us.
Sullivan
Now, of course, part of the motivation for doing that - wasn't that true? - came out of Hoyle's desire to show that there was another way to make the heavy elements besides in a hot big bang.
Burbidge
No, his original in 1946. His famous paper of 1946 where he showed how to make the iron peak elements in the interior of a star. And then he'd had time working with Fowler in Caltech in which they'd gone further than just the iron peak elements. And they looked at lighter elements.
Sullivan
But I bring up the cosmology because I was interested in how you viewed at that time, these source counts that you talked about or the steep slope that seemed to be quite inconsistent with the steady-state idea. First of all, what was your general feeling about steady-state versus an evolving universe, yourself, as an extra-galactic astronomer?
Burbidge
Well, by then, the scale of the universe had been expanded and the various areas of the original level had terminated. And many of them had been removed, and so the time scale -
Sullivan
That problem had gone away, yes.
Burbidge
So, there wasn't the bad discrepancy between the age of the solar system and the age of the universe.
Sullivan
Right.
Burbidge
So, I don't think - I particularly didn't have any strong leaning either way. Although, steady-state appealed to me more philosophically than the big bang cosmology. When we started - when we went to the University of Chicago and had access again to the McDonald telescope, we ceased at that point, really, to work on stellar spectra, which we'd been doing when we were at McDonald when we were in Chicago before, and started to work on galaxies. We had gotten interested in masses of galaxies from an early paper of one Martin Schwarzschild in the Astronomical Journal in 1954 that I described in the Journal Club in -
Sullivan
Well, that's the original motivation for that long series of papers?
Burbidge
It started it, yes. But so, we had two things to do. One was we wanted to look into getting a rotation curve in a more efficient way than just point by point as [Laurence] Aller and people had pioneered. And also to work on the nature of the radio galaxies. And one of the objects we particularly wanted to study was Centaurus A, a strong radio source. It was not even known at the time we started to work on it whether it was an external galaxy.
Sullivan
For sure, yeah. Right.
Burbidge
It had been a suggestion in the literature that it was a weird kind of planetary nebula. No, it was a declination minus 43 which could be reached from McDonald with difficulty [laughter]. And so, we tried. And that was where I had an accident on the telescope.
Sullivan
And what was that accident?
Burbidge
Well, we tried, first of all, to get it to the Cassegrain focus - the Cassegrain spectrograph, and we had all the lights out.
Sullivan
Yes, you were -
Burbidge
We had the Cassegrain platform therefore right up and the telescope low. And the Cassegrain platform came up in two halves and there was a gap in the middle. And to get the telescope spectrograph in, one took down - I had taken down the chains that guided you from stepping down low. The floor was high. I had all the lights out because it was difficult to see to set the slit on the right place on the galaxy. And in my excitement, I stepped down in the hole [laughter]. And luckily it was wintertime and I was well-padded up in wool clothes.
Sullivan
How many feet, roughly, are we talking about?
Burbidge
Oh, about 12 feet down onto a steel floor. And I must have fallen cat-like because I didn't break any bones. I carried the control panel with me that had the lights [laughter]. But what I did do is knock all wind out. It was like having a strong punch in the solar plexus and I could not speak. I could not draw a breath to speak. And I could hear the night assistant and Geoff shouting down from the Cassegrain platform, "Are you alright? Are you alright?” And I couldn't answer. And they had no light because I'd carried the panel with me. And I heard them fumbling to get to the steps to climb down. Eventually, I managed to draw a breath and said I'm all right. And then they came, picked me up and I was all right, but bruised all over.
Sullivan
So this Centaurus A data took a lot of effort, you're saying?
Burbidge
Yes. We then went to the prime focus later on, to do it properly. We decided we needed to go to the prime focus. And there with the telescope in the same nearly horizontal position, one could lie on the roof of the Coudé room and get into almost any position line of the spectrograph that you wanted. And so we did it that way, on the floor. Lying on the floor.
Sullivan
And so what did you make of Cen A?
Burbidge
Now when we got the rotation, we found that there was plenty of hydrogen gas, emitting H-alpha in the dust lane. And so we were able to - we got a rather definite rotation, that the dust lane was rotating. We made little attempt to do anything in the stellar component outside of the dust lane because the spectrograph was set to reach H-alpha, but you had very poor resolution as you went through -
Sullivan
I see.
Burbidge
- very poor polar transmission, as you worked through the region of the stellar lines passing H and K. So all we got was the rotation for the dust lane. And there was some irregularities in the rotation, suggesting what the dust itself looked to be suggesting. That it was a ragged kind of a very disturbed distribution.
Sullivan
But let me ask - we're running out of time over here, but let me ask more generally, how you viewed the effect that these radio sources had on extragalactic astronomy. I mean, did they bring in a new universe? Or did they just sort of modify the old one? Or what did it do to the way astronomy developed through the ‘50s and then the early ‘60s, set in the pre-quasar era?
Burbidge
The main problem was, what was the energy source? And that was a big puzzle. Because Geoff's earlier calculations had made it quite clear, that a big energy release was needed. And one suggestion that had been made by Minkowski in the observations of NGC 1275, he found two sets of velocities different by 3,000 km per second. And he suggested this energy could be provided by kinetic energy. Simply, collisional energy. Kinetic energy. Amplification by the collision of a pre-existing magnetic field and acceleration in the magnetic field of charged particles. Our calculation showed that you couldn't get sufficient amplification by collision. So that would not work and -
Sullivan
But what I was thinking is, is it a fair statement to say that radio astronomy was the means by which attention was drawn to the fact that it was not a quiet universe in terms of stars burning in galaxies.
Burbidge
Yes, it was the beginning of the era of the active universe as you know it.
Sullivan
Right. Although it wasn't clear that the nucleus really was the key, as we now think anyway.
Burbidge
Well it was -
Sullivan
Ambartsumian, of course, iwas pushing for that, but I don't think that was a general feeling at that time.
Burbidge
It was our feeling from our studies of NGC 1275, when we found that Minkowski's high velocity filament came into the nucleus, and the nucleus was a Seyfert nucleus after all, it was one of the original Seyfert galaxies, and we suggested that it was material being ejected from the nucleus.
Sullivan
Of course, Virgo A, M87, also was highly evocative -
Burbidge
Right. Yes.
Sullivan
- with this kind of thing. What did you make of Cygnus A, where the emission was coming from -
Burbidge
Oh, - Well, that clearly has been the objection, when nobody realized at that time though, how - they narrowly -
Sullivan
Blobs.
Burbidge
But you have two blobs. Where high energy particles must have originated at the center of the galaxy.
Sullivan
Well, but that's a big jump, to say that, isn't it? That they must have originated -
Burbidge
Well it, if you drew back the line, with galaxies in the center -
Sullivan
Well, that's true.
Burbidge
At least they’d come from the galaxy and the place where any activity from observations of nearer things like NGC 1275, there is activity in the nucleus.
Sullivan
So, you're saying anyway that you and your husband were working on the model that the nucleus really -
Burbidge
Yes.
Sullivan
- was the key to -
Burbidge
Yes.
Sullivan
- to how this developed.
Burbidge
Yes.
Sullivan
I'd like just to also ask about the very beginning of the quasar era. I think it's correct that you were not directly involved with the work the first few months at Caltech when the redshifts were identified and so forth.
Burbidge
No, but we were -
Sullivan
You got into it very quickly.
Burbidge
We still had some time at McDonald, and when I gave the Russell lecture, I decided to drag out this bit of history and reproduce some early spectra that we took at McDonald, at the prime focus of the 82 inch telescope of 3C 48. It was a good position of 3C 48.
Sullivan
Now, was this before the redshift was identified?
Burbidge
Yes.
Sullivan
Yes, okay.
Burbidge
Yes. And I think in the Russell lecture, I mentioned this is 20/20 hindsight and showed them the spectra, and you could actually see right in the red end H beta and the oxygen three line, but I only saw at the time, I only noticed one emission line, which I guess was the 5007 emission line, and one of the – of course we weren’t looking (?) to see anything else.
Sullivan
But going back to the data, you can see it there. Yeah.
Burbidge
Yeah. Yes, so I do have that reproduction somewhere.
Sullivan
What did you make of these stellar sources like 3C 48 at that time?
Burbidge
Didn't have enough data. It was about the limit of what you could get at the McDonald prime focus, and it was hard to set on and hard to guide on.
Sullivan
So, it really was almost confined to the 200 inch to do that kind of work.
Burbidge
And of course, the position with 3C 273 wasn't made generally public.
Sullivan
That's right.
Burbidge
[crosstalk] We could have observed that.
Sullivan
Yeah, right.
Burbidge
But, yeah, it was bright enough, but it was sent privately to Martin Schmidt and so (?) made the identification as soon as there became a reasonable number of identifications, and in 1962, when we went to Lick Observatory, went to the University of California and could use Lick Observatory, it was when I started working there, a prime focus was the 120 inch telescope, getting spectra of - just mainly collection redshifts. That was the idea to start with.
Sullivan
Right. And then you started a long program which is beyond my - I'm sort of cutting my study off in the late ‘60s. One last question, do you see any effects - and don't let me lead you in this question. If you say no, no is a perfectly good answer. Do you see any ways that radio astronomy through this era influenced the way optical astronomy was done, in its style or its content? Or is that -
Burbidge
Yes. Well, certainly it made one realize that something had to be done to improve methods of detection and spectrographs.
Sullivan
So you think that it pushed that along faster?
Burbidge
It pushed that along. It used to take me five hours sitting on one exposure at the prime focus cage of the 120 inch telescope. Well that doesn't compare with 10 days that Humason used to sit.
Sullivan
Right. It's sort of a long time.
Burbidge
It still felt a long time.
Sullivan
Right. So in the desire to do spectroscopic work on these faint sources, that was a driving force, you're saying?
Burbidge
It was certainly a driving force at Lick Observatory with Joe Wampler to develop -
Sullivan
In the ‘60s, yeah.
Burbidge
Yeah. Well he got his going in the early ‘70s.
Sullivan
And what about the aspect - by style I mean the way that the radio astronomers who were much more the kind of thinking of, "Let's put out a quick paper," and it's much more today's kind of science as opposed to the traditional observatory where you have lots of unpublished data and you eventually put out a complete study.
Burbidge
Well I used, in those days, to put out - as for our rotation curves, we used to put them out one by one as we got them. We'd put out - I'd put out like a dozen redshifts in the paper, whereas -
Sullivan
So did you feel yourself influenced at all by how things were going in various - it kind of sounds as though you didn't. You don't feel like the way that was happening in radio astronomy was influencing how you were doing, how you were doing optical astronomy.
Burbidge
Well, it made me gradually switch from working on galaxies, although it continued a little bit, to spending time working on quasars and the discovery of the first absorption lines in the 1960s -
Sullivan
Right. But I was thinking of more the style of how you did things rather than the actual scientific content. In other words, in terms of -
Burbidge
Well I was working with, instead of working with nice white stars and getting Coudé spectra that would take -
Sullivan
Yes. Well that's right. Right.
Burbidge
- forever to analyze, it was working with the little spectra of half an inch or so long.
Sullivan
It gave you the motivation to do this incredibly difficult work with very faint things, which had only been brought to the fore because of the radio -
Burbidge
Yeah. And we had no TV guidance, of course. It was all setting on the spectrograph, so it had to be done by eye. And I used to have ways of - my eyes in that time were pretty good at seeing faint light sources. People used to laugh that I used to keep a black patch over my guiding eye, so had to get into any light to keep the dark adaptation of that eye. And I could set 19.5 magnitude at the prime focus of the three-meter telescope - remember, the sky was much less bright in those days. But that was my limit that I could set on.
Sullivan
That's damn good. Well thank you very much. That ends the interview with Margaret Burbidge on 14th April 1988.