Wallace Sargent

Weart:

Interview with Wallace Sargent by Spencer Weart, June 10, 1975 California Institute of Technology. Nobody will use this recording without checking with you first. At least nobody will quote from it.

Sargent:

— Not even the CIA.

Weart:

That’s right, as a matter of fact, because they don’t know we have it.

Sargent:

That’s the safest way of keeping things.

Weart:

Well, the sort of thing I want to know is, for example, who are the deceased people whose papers we should know about? Also who are the people to be interviewed, or to know more about? What do people think are the most important developments in the postwar? Talk about things that happened while you are aware of them rather before you actually entered the field. So what do you think have been the most important developments? Who did them?

Sargent:

It’s a little difficult to say, who did them. Well, one can go back and read the literature of course. Well, as a generality, I would say that stellar evolution and stellar interiors is a major subject which has been essentially completed since the war. Of course, one says “completed” with a certain amount of trepidation, because often things turn out not to be that. For example, the solar neutrino controversy does cast doubt on whether, the accepted ideas of the interior of the sun and therefore on the interior of the stars are correct. After I read the new book on molecular biology by Albee “The Pact to the Double Helix”, it seemed to me that particular book is made good because there was a subject which was finished. Let’s say a synthesis was arrived at, on two fronts, first the discovery of DNA and then the possibility of replication, then the problem was solved. Also what Crick called the central dogma, the idea that — which is, that information can travel in only one direction, or a chain was put forward as a kind of synthetic idea. One of the problems of astrophysics is that this kind of synthesis, by and large, doesn’t exist. It strikes me that if you’re thinking about historical methods; you either have to tackle those subjects in which there does seem to be some kind of theoretical completeness— for example stellar evolution— or, you can deal with the discovery of as yet unexplained phenomena. One must start with a discovery.

Weart:

Well, part of my job, you see, is to store up material for future historians’ use. It seems like it makes sense to do something while it’s in process, and put it away in the archives. How nice it would be if someone had gone around and interviewed people while they were discovering the double helix, or whatever.

Sargent:

Yes, indeed. Of course Albee made attempts to talk with people who made contributions even if they are not retired like Pauling and that was successful to some extent. But, of the major subjects, it looks like stellar evolution, stellar interiors, and nuclear synthesis are fairly complete subjects, although by no means have every end been wrapped up.

Weart:

But you see a big step.

Sargent:

You can see — yes, you can see an enormous step forward for example in the case of stellar evolution. I think that everybody believes now that stars are made out of interstellar gas, and that they eject material back into the remaining gas, enriching it in the heavy elements and succeeding generations of stars are more and more enriched in heavier elements. I think that’s a view which everybody would subscribe to, and one which was first proposed just after the war. That’s the kind of dogma which looks as if it is here to stay. If anybody found an exception to that, for example, a pre-galactic sun, some kind of object that had apparently been condensed before the formation of the galaxy that would be an extraordinary revelation. Of course, such objects might exist.

Weart:

But probably not.

Sargent:

Probably not. That general kind of synthetic idea has been arrived at.

Weart:

Are there any names that come to mind for the whole development of nuclear synthesis and stellar interiors, stellar evolution?

Sargent:

Well, the main people which come to mind on the theoretical side are Fowler, Salpeter, and Schwarzchild. Those are the main names that come to mind. On the observational side, Greenstein, E.M. Burbidge, Unsold come immediately to mind.

Weart:

Do you think observation played an important part in this?

Sargent:

To my mind, it is one of the few subjects in astrophysics where observation played about the same role as theory. It is usually the other way around. Marvelous things are discovered or explained later — there’s very seldom prediction. But in this particular subject, there was a fair amount of theoretical work which might lead to observational consequences being followed out.

Weart:

Unlike the usual case.

Sargent:

Unlike the usual case, yes. But it’s a perfectly beautiful subject, to me, because of the close interaction between theory and observation. For example, Royle, predicted that because red giants exist, these had to be given by the Triple Alpha process. And in turn, this meant that there had to be a particular excited state of carbon, carbon-12, which was then found by nuclear physicists. There are similar thoughtless spectacular examples of actual observations of stars, all the time, in that particular subject. I got into that subject actually myself toward the end of it. And all processes of stellar evolution are still not even finished. The end points of stellar evolution are not understood. It was not known whether massive stars become black holes, and less massive stars become neutron stars, and less massive stars become white dwarfs, or where the boundaries between these possibilities were, but at least I think we now believe that those are the three end points of stellar evolution. It’s only a question of working out the details. It is unlikely there are other possibilities. So in that sense, it’s a complete subject. As compared with other matters, it’s just a question of working out the details, although that is quite incredibly complex. But generally, in that whole business, there’s enormous interplay between theory and observation, which you don’t normally get, with modern astrophysics.

Weart:

What other issues then?

Sargent:

There’s the general problem of the structure of the galaxy, which I think has been cleaned up since the war, with the help of the 21 centimeter observation. The idea of stellar populations and the kinematic difference between the halo of the galaxy and the disk of the galaxy’s another.

Weart:

What names would you associate with that?

Sargent:

Oort in particular and Baade, who is now dead.

Weart:

Where’s his papers, do you know?

Sargent:

I believe that they’re in Gottingen. His wife took them. I don’t know what she did with them.

Weart:

I believe they’re back here. I think they’re in the attic, and I think they’re wrapped up. Somebody told me they’re wrapped up in parcels in the attic over at Santa Barbara St.

Sargent:

Well they should certainly be looked at, because Baade published very little in those years, on the work he did.

Weart:

I think that’s right. Many of the papers at Santa Barbara St., are locked away right now. I must see if I can somehow get a look at them.

Sargent:

Baade usually communicated by conversation rather than by writing.

Weart:

Perhaps more by letters.

Sargent:

— but I think every afternoon, he would go to his office and talk to anybody who would come around, lots of astronomers knew that. You’d just drop in, to get his opinions on subjects. He had a very wide influence. Although I never met him, I understand he had a very wide influence, without publishing a great deal.

Weart:

His papers would be very interesting to look at.

Sargent:

Yes. There was a conference in 1958 on stellar populations, run by the Vatican, in which a few people attended. I should think the major participants would be the major contributors to galactic structures. In addition to stellar interiors, there is the general structure of the galaxies. Then there was the problem of the evolution of our galaxy and other galaxies, which is the subject now, in my opinion, making the most progress in astrophysics, among the general subjects. This is based on the idea that we discussed before, that the galaxy was born as pure hydrogen and helium, and then stars, were made and those stars contaminated the remaining stars with heavy elements and then succeeding generations of stars were born, more and more enriched. There are attempts now to see why one galaxy differs from another, and the rate at which it uses its gas up, and why some galaxies have only used up 50 percent of their initial gas, and others have used up all of it, essentially, and how this correlates with the appearance of the galaxy, a regulars lying at one end of the sequence, and the elliptical at the other end. The essential problem in this whole business understands the details of star formation, and in particular understanding what determines the mass spectrum of which stars are formed, and how many 10 mass stars there are, relative to how many mass stars. Empirically this is another subject which is more typical of astrophysics, in that observation leads theory. Empirically, it appears that galaxies don’t differ all that much, in the relative proportions of stars of different mass. There seems to be a more or less magic distribution of the mass at which stars are born. That’s been discovered fairly recently the evidence is fairly indirect. It is something I’ve worked on myself. I have perhaps made what turns out to be a fairly important contribution.

Weart:

It sounds very interesting.

Sargent:

It does imply that there’s a kind of fundamental theory that would determine distribution of stars over mass, which in turn determines the efficiency with which a given generation of stars can make heavy elements. Because the low mass ones don’t make heavy elements, the high mass ones do, and if there’s a constant ratio of high mass stars to low mass stars per generation, then they would always make heavy elements with the same efficiency.

Weart:

Right.

Sargent:

And that efficiency turns out to be about 1 percent, a fairly easy number to remember. For every amount of mass that’s condensed into stars, roughly 1 percent gets made into heavy elements. And that seems to be a universal thing, which is the same overall from one galaxy to another. And therefore there must be some underlying theory.

Weart:

Although so far there isn’t.

Sargent:

So far, there isn’t concerning that whole business, understanding then why some galaxies make stars faster than others.

Weart:

Are there some other names you would associate with this, whole galactic evolution problem?

Sargent:

Schmidt has made fundamental contributions, though not for ten years or so. Oort again. Among the younger people, working actively in the field now, Searle.

Weart:

Is that Searle?

Sargent:

Searle. Arnett, Beartice, Tinsley who’s now at Yale, Richard Larsen, who’s now at Yale. Of course, there’s something chauvinistic about this. There are people in other countries too. But you asked me, off the top of my head.

Weart:

Right.

Sargent:

OK, so that’s a subject which is now making rapid progress. As far as we can see, it doesn’t involve any unknown physics. It involves the physics of stellar interiors, which is hopefully pretty well wrapped up. The details involve knowing what is the ultimate fate of massive stars, whether they become black holes or not? Because if a star makes all of its interior into say iron, and then that collapses into something that never gets chucked out into the interstellar gas, that makes a big difference to enrichment, than if it chucks out nine of the ten stellar masses. So, now there are problems like still to be resolved, but because it’s unlikely that exotic physics plays a role, it’s making rapid progress.

Weart:

I see. Yes.

Sargent:

The general question of the evolution of galaxies is also terribly important for understanding the cosmological problem, because people try to determine the overall structure of the universe by looking at distant galaxies, measuring the brightness, etc. If the brightness’s in the past were different from what they are now, you have a problem, unless you can actually calculate what they were. That’s a really important part of the subject which some people are working on very seriously, particularly Cunn and Beartice Tinsley.

Weart:

And of course no one knows exactly where a galaxy comes from in the first place.

Sargent:

Yes. When I said that the question of galactic evolution was making rapid progress, it is indeed except for the beginning. Nobody understands how galaxies arise as you say. So as far as I can see, that particular part of it is making no progress whatsoever. But once Seyfert galaxies one can make some sense about how they evolve and die, you can look too.

Weart:

Ok.

Sargent:

I think that’s a particularly interesting subject that you might keep an eye on, just because something’s happening in it. Now, the other major field is of course that of violent events in galaxies, which was discovered through radio astronomy sources. I think by and large, in the quasar, Seyfert galaxy, radio galaxy matter they are all manifestations of some, I think, common underlying phenomenon that we don’t understand. There, observation has dominated completely. There’s essentially no theoretical understanding in the field, no predictions of any kind.

Weart:

No one has any idea what’s happening.

Sargent:

No. I think the only theoretical idea which is almost certainly right is that the radio emission is synchrotron radiation, in radio galaxies, quasars and so forth. But, what the optical emission really is, and what excites the optical emission lines and things optically, I think is not understood. What produces the optical continuum is not understood. It may be optical synchrotron radiation, but it might be other things, even things that we haven’t yet thought of. And that’s a subject in which theory is way, way behind. Observation has completely dominated. So I think any kind of historical analysis of that subject couldn’t possibly be like the path to the double helix. Because essentially you need a theoretical synthesis, I think, to make a complete story. If all you’ve got is some random observations, which you vaguely recognize to be manifestation of the same unknown phenomena, it’s not so interesting.

Weart:

I understand your point.

Sargent:

But of course, understanding how the observational stuff arose, and why it was, for example, that radio astronomers discovered these phenomena and not optical astronomers, is an interesting, sociological question. Where were we?

Weart:

You mentioned some of the main events. I wondered whether there might be some people who may not be well known for any discoveries they made, but perhaps more important as teachers?

Sargent:

Probably.

Weart:

Perhaps there were people who played an important role in building instruments?

Sargent:

Well, it’s been a peculiar business, in optical astronomy, because for the several years after the war, Hale and the old timers still dominated because the main discoveries were made with the 200 inch, the 100 inch and the small telescope at Lick. It’s only been in the late 1960’s I guess, or mid 1960’s and after, that all the telescopes that were made since the war made important contributions. That’s very peculiar it’s not true of other subjects. In radio astronomy, the things that Ryle made just after the war were immediately important, and everywhere the radio telescopes were built, just a few years before they made productive discoveries.

Weart:

Have there been any important advances in instrumentation? These are the kinds of things that often tend to get overlooked, when someone invents a new way.

Sargent:

Yeah. Well, just after the war, photomultipliers were used for the first time in astronomy, and photocells of various kinds had been used, but they were very insensitive, and the photomultiplier — of first revolutionized photometry. That had an enormous impact on stellar evolution, and was not used by the people who made the technical advances at all. I think Eggen was one of the first really to make photoelectric color magnitude diagrams.

Weart:

How’s that spelled?

Sargent:

Eggen, and Sandage, in the early 1950’s. But Eggen was one of the very first people, who really understood the relationship of what he was doing to stellar evolution. There were other people who made color magnitude diagrams of clusters, who did it; because other people said it was a good thing to do. I don’t think Johnson, for example understands the astronomical implications of what he’s doing. Eggen and Sandage and Arp made important contribution. The photographic plate has been pretty much the same over time, and there hasn’t been much improvement in it. Oh, there’s one technical thing which has had enormous influence, which is often overlooked, the Palomar sky survey. Practically no faint objects in astronomy have been done without the use of the Palomar sky survey.

Weart:

You know you’re the first person to mention that. Who would you say was responsible for that?

Sargent:

I don’t know who had the idea of doing it. It was actually carried out by Minkowski, who’s still alive, and around 80 years old, at Berkeley. And George Abell over at UCLA did a lot of the work as an assistant, when he was a student.

Weart:

Oh, I didn’t know that. Was that a long time ago?

Sargent:

Yes, that was some time back. But once I went to the Southern Hemisphere a few years ago to work on. It was tremendously more difficult, because no survey existed down there. You just couldn’t get findings on these very precisely things. For example, a radio astronomer that located a source you just had no idea what it could be from, because there was no photograph of that part of the sky that he could refer to. I think that the existence of the survey has been one of the main factors in successful identification of radio sources and x-ray sources. It would have been tremendously more difficult without that.

Weart:

That’s exactly the kind of thing that I find interesting, because it’s something that even I take completely for granted.

Sargent:

I’ve often thought about how important the sky survey was, but I never reflected on, whether whoever thought of it, thought of it for the kind of use that it’s been put to, or whether they had some other idea in mind. I just don’t know. Because before there have been huge cataloguing jobs done in astronomy, like tables of things, and sometimes these have been enormous successes, and others failed miserably. It’s very hard to predict, I would thing, whether that sort of thing is going to be useful.

Weart:

Has there been any great job of tables done since the war?

Sargent:

No. Only radio sorts. But there have been improvements, on accurate positions of stars, things of that sort, international collaborations, setting up frameworks of accurately known positions of stars, which can be used in turn for determining accurately the position of newly discovered things.

Weart:

I was thinking of tables of galaxies, I suppose.

Sargent:

Well, Zwicky catalogue of galaxies has been very important. But that’s about the only thing.

Weart:

That’s Zwicky back there, isn’t it?

Sargent:

Yes. Zwicky’s my great hero. He should certainly be mentioned in any history of modern astronomy.

Weart:

Right. So far everybody’s mentioned his name.

Sargent:

I was reflecting the other day whether or not Zwicky was the first who can be considered the father of high energy astrophysics, the first to realize that there were very high energy things going on. (Interruption) By the way, usually I don’t get many telephone calls at all. I’m not given to either getting or making telephone calls.

Weart:

To get back to instruments, is there anything radically different about what you use in your observation now from what you would have done 20 years ago?

Sargent:

There is now. In the last few years, two things have happened for optical astronomers. One is the television finding. Yeah, we don’t look at the sky with our eyes any more. We have a television screen, and look at it in a brightly lit room, and you can see much fainter than you can with your eye. Also, you can look at your charts and your pictures without ruining your dark adaptation. You can make measurements on the screen, to figure out exactly where a thing you can’t see ought to be. And then, just recently in spectroscopy, various kinds of more sensitive devices have come into existence. First of all, image tubes, which have been used since perhaps the middle 1960’s, are now being replaced by other television devices, for actually measuring spectra. I’ve been using one that was designed in England, which technically superior to anything else that’s existed spectroscopically.

Weart:

What’s the English firm?

Sargent:

EMI makes them. But the actual design of instruments has been done by Boksenberg. Well, that is still in the development stage. But we’ve got a lot of good results out of it already. We can work on with a focus on objects of the 17th magnitude, quasars, where previously, 12th magnitude stars would be difficult.

Weart:

17th magnitude?

Sargent:

Yes. It’s made an enormous difference.

Weart:

Well, I’m curious also about how things may have changed, not just in strict science but in terms of the social environment that is the kind of life you lead, in terms of administration or traveling, publications and so forth. Is it very different from what is with your professors when you were a student?

Sargent:

The one thing that’s changed I think is that teamwork is creeping into astronomy. It was always practically a lone occupation. The typical state of affairs for an observer would be that there would be several standard pieces of observatory equipment, like a photo meter, a spectrograph, a direct plate holder and the astronomer would use those things, and they wouldn’t usually build their own equipment. They would usually do things by themselves. Now things are getting more complicated. It’s common at least in the things I’m working on, three or four authors to work on a paper that would have taken one chap, 10 or 20 years ago. And the pace of technical development is increasing terrifically. It’s no longer possible, I think, to use the same piece of equipment year after year after year, on a big project like we used to do. You really have to keep up maybe if not keep up yourself with the technical developments at least know people who are keeping up and get their opinion on what is best to use. This has meant a lot of loosening up, I think, on the big telescopes, which used to be organized in a very rigid way, although I think it was not a sort of legal regimentation, more by tradition. But when I first came here as a post-doc, which was only about 15 years ago, some people in the Hale Observatory worked on stars, and they weren’t allowed to work on galaxies, and the ones who worked on galaxies were restricted in various ways. For example, when radio sources were first identified, in extragalactic objects Greenstein told me that he was allowed to work on the ones inside the Virgo cluster, and Minkowski had everything outside the Virgo cluster. It’s never been clear to me how rigid that really was, and how strongly it would have been enforced, in practice, if a guy stepped outside of his boundaries. But as a practical matter, people actually did observe the conventions that were set either by group hysteria or some other mechanism. Generally, there was always great reluctance to tread on other people’s toes.

Weart:

Was that only true here, do you think or was it true in general?

Sargent:

In general. Partly because astronomy was such a large subject, with very few large telescopes, and it was probably best for the subject, for people to spread themselves vary widely. And at the same time, it had the effect that results didn’t get checked on. For example, when the Stebbins-Whitford effect was discovered, it was a fairly technical matter, but Stebbins and Whitford in the early 1950’s found that distant galaxies were redder than nearby ones, by an amount which was not just due to the red shift. They were supposedly intrinsically redder. And this was used for several years as an argument against the steady state theory, which is almost certainly wrong for other reasons, but of course the very same theory would say that wherever you look in space, everything looks as though the same. It looks like an intrinsic difference, in large distances. This thing hung on for years, and was then quietly shown to be wrong. I think Stebbins and Whitford themselves found it was wrong, but never published a retraction. It was just passed around by word of mouth. This was no longer an argument against the steady state theory. And there were several instances of that kind, which were just due to, first, the lack of large telescopes, the lack of competitions but secondly, due to the convention that you didn’t compete.

Weart:

This would not be so likely to happen today at all.

Sargent:

No.

Weart:

There’s more competition, which is partly the result of the new telescopes and partly because, though to a lesser extent, outsiders have been brought into the game, because of their technical competence. People, who don’t understand the old astronomical traditional conventions, are not inhibited by them.

Weart:

Have there been any changes in the way one publishes things or the way one hears about things?

Sargent:

Not around here. There might be a slightly greater tendency for people to publish marginal results, in case somebody discovers it someplace else. But I think it’s not a very marked trend. That’s my opinion. Other people might differ. There are some things in astronomy where it’s certainly not the case, where there is intense competition to publish. But optical astronomers seem to be slightly gentler than, for example, millimeter astronomers who, there’s fantastic rivalry, lots of hatreds built up, lots of competition. The pace, at which the journals come out, as you know, has gotten ridiculous. It’s impossible to keep up. I think it would be better for the work for people to spend more time refereeing to save the rest of the world the problem of having to read garbage. It should go through a filtering process. It would be better. Having everybody have to do the filtering is very stupid. It’s a waste of time. But I don’t think the pace of discovery has risen to the extent that the number of publications has gone up. The number of publications, or the number of pages published, keeps pace with the number of astronomers. I think somebody has shown that statistically

Weart:

Rather than —?

Sargent:

— rather than the quality of work, yes.

Weart:

You feel that the pace of discovery has picked up, though? Over let’s say 20 years ago?

Sargent:

I find that very hard to say, because the pace of things that are announced as discoveries has picked up. That’s because of competition. I just don’t know.

Weart:

Do you have the same sort of feeling about the field now that you had 20 years ago in terms of how exciting it is?

Sargent:

Yes. I think I was still in high school 20 years ago. Yes, 15. Zwicky taught that there would be no end that, first of all, any careful repetition of a piece of work already done would lead to new things, and also that there would always be new things to be discovered anyway, and I tried to think that’s true. There’s a big difference among astronomers who work on extra-galactic things — a big difference of opinion and Sandagethinks that after cf° (q°?) and H° had been accurately determined there would be nothing left. That would be it. There would be a least what he calls a plateau. With nothing more to be discovered. Well, I disagree with that very strongly... And of course, I can’t say in what respect things —

Weart:

— you can’t say what surprising things will happen.

Sargent:

Of course not. But I think that in some way, it’s foolish to extrapolate from the past, when there have always been new things turning up. It was the mistake made by 19th century physicists, to say that Newton’s laws explained everything, and that understanding the atomic structure was only a question of detail.

Weart:

Actually, modern historical research indicates that that’s not what they really thought.

Sargent:

Really? OK. I hope not anyway. But there are certainly people around who follow what is popularly supposed that 19th century physicists thought.

Weart:

Namely, that they don’t think that the thing is finished, but they think that it can be finished fairly soon?

Sargent:

Yes.

Weart:

They feel they’re arriving at a time when some great synthesis will be reached, some important plateau.

Sargent:

Yes. I disagree. I think that the question of the evolution of galaxies, given the existence of galaxies, might be solved in the next ten years, just like stellar evolution is in that sense a fairly well understood subject. But I don’t believe that these other things, like what makes quasars work, what is the overall structure of the universe, are questions which will be cleared up very soon at all. And I disagree with SANDY mainly because I don’t think that the determination of q° and H° is the main problem with extragalactic — I think the main problem is to understand the physical laws that govern the large scale structure of the universe. What these chappies do is to assume that general relativity applies to the universe at large, and then determine tow parameters which can be fitted into general relativity is theory. But usually with the kind of data that you have available, in actually you can always fit two parameters to any theory. Unless, you know, it would have to be wildly wrong??? And it must require much more completed effort to find out that the equations are wrong. And not whether your two parameters —

Weart:

— not whether the two parameters are — Well, I think this would be a good place to stop.