Oral History Transcript — Dr. Wallace Leslie William Sargent
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Wallace Leslie William Sargent; June 10, 1975
ABSTRACT: Preliminary discussions of some important developments in astronomy, from stellar evolution and stellar interiors to the evolution and structure of galaxies and their importance for understanding the cosmological problem. Comments on optical astronomy, television finding and image tubes. The Palomar Sky Survey; comments on Zwicky. Changes in the social environment, competition and publication. Thoughts on the future of astronomy: research.
WeartInterview 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.
WeartThatís right, as a matter of fact, because they donít know we have it.
SargentThatís the safest way of keeping things.
WeartWell, 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?
Itís 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 ďcompletedĒ 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 ďThe Pact to the Double HelixĒ, it seemed to me that particular book is made good because there was a subject which was finished. Letís 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, doesnít exist. It strikes me that if youíre 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.
WeartWell, part of my job, you see, is to store up material for future historiansí use. It seems like it makes sense to do something while itís 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.
SargentYes, 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.
WeartBut you see a big step.
SargentYou 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 thatís a view which everybody would subscribe to, and one which was first proposed just after the war. Thatís 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.
WeartBut probably not.
SargentProbably not. That general kind of synthetic idea has been arrived at.
WeartAre there any names that come to mind for the whole development of nuclear synthesis and stellar interiors, stellar evolution?
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.
WeartDo you think observation played an important part in this?
SargentTo 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 — thereís 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.
WeartUnlike the usual case.
Unlike the usual case, yes. But itís 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. Itís only a question of working out the details. It is unlikely there are other possibilities. So in that sense, itís a complete subject. As compared with other matters, itís just a question of working out the details, although that is quite incredibly complex.
But generally, in that whole business, thereís enormous interplay between theory and observation, which you donít normally get, with modern astrophysics.
WeartWhat other issues then?
SargentThereís 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 galaxyís another.
WeartWhat names would you associate with that?
Oort in particular and Baade, who is now dead.
WeartWhereís his papers, do you know?
SargentI believe that theyíre in Gottingen. His wife took them. I donít know what she did with them.
WeartI believe theyíre back here. I think theyíre in the attic, and I think theyíre wrapped up. Somebody told me theyíre wrapped up in parcels in the attic over at Santa Barbara St.
SargentWell they should certainly be looked at, because Baade published very little in those years, on the work he did.
I think thatís 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.
SargentBaade usually communicated by conversation rather than by writing.
WeartPerhaps 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. Youíd 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.
WeartHis papers would be very interesting to look at.
SargentYes. 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 donít 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. Thatís been discovered fairly recently the evidence is fairly indirect. It is something Iíve worked on myself. I have perhaps made what turns out to be a fairly important contribution.
WeartIt sounds very interesting.
SargentIt does imply that thereís 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 donít make heavy elements, the high mass ones do, and if thereís a constant ratio of high mass stars to low mass stars per generation, then they would always make heavy elements with the same efficiency.
SargentAnd that efficiency turns out to be about 1 percent, a fairly easy number to remember. For every amount of mass thatís 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.
WeartAlthough so far there isnít.
SargentSo far, there isnít concerning that whole business,
understanding then why some galaxies make stars faster than others.
WeartAre there some other names you would associate with this, whole galactic evolution problem?
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.
Is that Searle?
Searle. Arnett, Beartice, Tinsley whoís now at Yale, Richard Larsen, whoís now at Yale. Of course, thereís something chauvinistic about this. There are people in other countries too. But you asked me, off the top of my head.
SargentOK, so thatís a subject which is now making rapid progress. As far as we can see, it doesnít 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 itís unlikely that exotic physics plays a role, itís making rapid progress.
WeartI see. Yes.
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 brightnessís in the past were different from what they are now, you have a problem, unless you can actually calculate what they were. Thatís a really important part of the subject which some people are working on very seriously, particularly Cunn and Beartice Tinsley.
WeartAnd of course no one knows exactly where a galaxy comes from in the first place.
SargentYes. 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.
SargentI think thatís a particularly interesting subject that you might keep an eye on, just because somethingís 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 donít understand. There, observation has dominated completely. Thereís essentially no theoretical understanding in the field, no predictions of any kind.
WeartNo one has any idea whatís happening.
SargentNo. 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 havenít yet thought of.
And thatís a subject in which theory is way, way behind. Observation has completely dominated.
So I think any kind of historical analysis of that subject couldnít 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 youíve got is some random observations, which you vaguely recognize to be manifestation of the same unknown phenomena, itís not so interesting.
WeartI understand your point.
SargentBut 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?
WeartYou 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?
WeartPerhaps there were people who played an important role in building instruments?
Well, itís 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. Itís only been in the late 1960ís I guess, or mid 1960ís and after, that all the telescopes that were made since the war made important contributions. Thatís very peculiar itís 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.
WeartHave 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.
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.
WeartHowís that spelled?
Eggen, and Sandage, in the early 1950ís. 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 donít think Johnson, for example understands the astronomical implications of what heís doing. Eggen and Sandage and Arp made important contribution.
The photographic plate has been pretty much the same over time, and there hasnít been much improvement in it.
Oh, thereís 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.
WeartYou know youíre the first person to mention that. Who would you say was responsible for that?
SargentI donít know who had the idea of doing it. It was actually carried out by Minkowski, whoís 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.
WeartOh, I didnít know that. Was that a long time ago?
SargentYes, 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 couldnít 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.
WeartThatís exactly the kind of thing that I find interesting, because itís something that even I take completely for granted.
SargentIíve 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 itís been put to, or whether they had some other idea in mind. I just donít 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. Itís very hard to predict, I would thing, whether that sort of thing is going to be useful.
WeartHas there been any great job of tables done since the war?
SargentNo. 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.
WeartI was thinking of tables of galaxies, I suppose.
SargentWell, Zwicky catalogue of galaxies has been very important. But thatís about the only thing.
WeartThatís Zwicky back there, isnít it?
SargentYes. Zwickyís my great hero. He should certainly be mentioned in any history of modern astronomy.
WeartRight. So far everybodyís mentioned his name.
SargentI 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 donít get many telephone calls at all. Iím not given to either getting or making telephone calls.
WeartTo 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?
SargentThere is now. In the last few years, two things have happened for optical astronomers. One is the television finding.
Yeah, we donít 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 canít 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 1960ís, are now being replaced by other television devices, for actually measuring spectra. Iíve been using one that was designed in England, which technically superior to anything else thatís existed spectroscopically.
WeartWhatís the English firm?
SargentEMI makes them. But the actual design of instruments has been done by Boksenberg.
Well, that is still in the development stage. But weíve 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.
SargentYes. Itís made an enormous difference.
WeartWell, Iím 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?
SargentThe one thing thatís 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 wouldnít usually build their own equipment. They would usually do things by themselves.
Now things are getting more complicated. Itís common at least in the things Iím 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. Itís 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 werenít 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. Itís 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 peopleís toes.
WeartWas that only true here, do you think or was it true in general?
SargentIn 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 didnít 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 1950ís 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 didnít compete.
WeartThis would not be so likely to happen today at all.
WeartThereís 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 donít understand the old astronomical traditional conventions, are not inhibited by them.
WeartHave there been any changes in the way one publishes things or the way one hears about things?
SargentNot 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 itís not a very marked trend. Thatís my opinion. Other people might differ. There are some things in astronomy where itís 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, thereís fantastic rivalry, lots of hatreds built up, lots of competition.
The pace, at which the journals come out, as you know, has gotten ridiculous. Itís 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. Itís a waste of time. But I donít 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
WeartRather than —?
Sargent — rather than the quality of work, yes.
WeartYou feel that the pace of discovery has picked up, though? Over letís say 20 years ago?
SargentI find that very hard to say, because the pace of things that are announced as discoveries has picked up. Thatís because of competition. I just donít know.
WeartDo you have the same sort of feeling about the field now that you had 20 years ago in terms of how exciting it is?
SargentYes. 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 thatís true. Thereís a big difference among astronomers who work on extra-galactic things — a big difference of opinion and Sandagethinks that after cfį (qį?) and Hį 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 canít say in what respect things —
Weart — you canít say what surprising things will happen.
SargentOf course not. But I think that in some way, itís 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 Newtonís laws explained everything, and that understanding the atomic structure was only a question of detail.
WeartActually, modern historical research indicates that thatís not what they really thought.
SargentReally? OK. I hope not anyway. But there are certainly people around who follow what is popularly supposed that 19th century physicists thought.
WeartNamely, that they donít think that the thing is finished, but they think that it can be finished fairly soon?
WeartThey feel theyíre arriving at a time when some great synthesis will be reached, some important plateau.
SargentYes. 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 donít 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 donít think that the determination of qį and Hį 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.