Seth Shostak

De Swart:

Hi, this is Jaco de Swart. Is this Seth I'm speaking with?

Shostak:

It is.

De Swart:

Oh, look at that. I'm Jaco. I'm calling you all the way from Amsterdam. We've exchanged a couple of emails.

Shostak:

Yeah, that's right. Hang on, let me shut the door here.

De Swart:

Yeah, of course.

Shostak:

Okay, still there?

De Swart:

Yes.

Shostak:

Okay.

De Swart:

I guess there's a bit of a delay, but it's great to speak to you. It's an honor, actually. [Laughs] It's great that Gianfranco brought us into contact. I of course knew about your early work. I'm a PhD student at the University of Amsterdam and I'm working on the history of the dark matter problem.

Shostak:

Why?!

De Swart:

[Laughs] 

Shostak:

So, you're in Amsterdam, right?

De Swart:

Yeah.

Shostak:

How's your Dutch?

De Swart:

[Pretty good.]

Shostak:

[Laughs] [Yes, sounds pretty good.]

De Swart:

No, I'm native. Ik ben Nederlands.

Shostak:

Oh, yeah? That so? Okay, okay. Were you born in Amsterdam?

De Swart:

No, in Nijmegen.

Shostak:

Nijmegen? Okay.

De Swart:

Yeah. [Laughs] But apparently you do have some Dutch skills?

Shostak:

Yeah, very few, we kept in touch in Groningen.

De Swart:

Ah yeah, Groningen. [Laughs]

Shostak:

Yeah, I would stay in the sterrenkunde afdeling [astronomy department] in Groningen.

De Swart:

In Kapteyn.

Shostak:

Anyhow, but my Dutch is gone. I left there in 1988.

De Swart:

1988, ah. And okay, and on whose invitation was that, or was that a visitorship, or?

Shostak:

Well, I don't even remember. I was just a wetenschappelijk medewerker [research assistant/worker] at the university, and so I was there mostly using the Westerbork telescope.

De Swart:

Ah yeah of course.

Shostak:

Research galaxies, yeah.

De Swart:

And so that was still the moment you were studying galaxies with radio?

Shostak:

Yes, 21cm.

De Swart:

21cm. Indeed.

Shostak:

Yeah, rotation curves mostly.

De Swart:

Yes, oh, look at that. So, and when did you start your study? Like when did you start to study at all?

Shostak:

Well, you know, I was a grad student at Caltech beginning in 1965. '65. And it was possible then, Caltech had an interferometer, not like Westerbork. Westerbork has 14 antennas that are a decent width. But Caltech had two at that point. But, you know, if you studied galaxies, they don't move very fast, so you can use the antenna for months making observations and come up with a detailed map. So, I was doing that for my thesis, and my thesis advisor was helping me. And we studied I think seven different galaxies, and many of them were late type spiral galaxies. And I remember reducing the data for these things, making maps, and getting rotation curves. So, that would have been about 1968.

De Swart:

Ah yes.

Shostak:

And you know, everybody expected that the rotation curves would be kept in the area, that in the outer regions of the galaxies, the spinning would slow down. And I assume that you know all this kind of stuff. But they weren't, the rotation curves were flat. And I remember walking back and forth to the Rankin Center, the computer center at Caltech, trying to think of ‘where was the error in my software?’

De Swart:

[Laughs] So, what kind of software were you using?

Shostak:

Well, we wrote it ourselves. It was, you know, a scheme that had been cooked up actually in Leiden, eventually, but that's a different story about the software. But, so you know, in my thesis, you'll see these flat rotation curves. Now when I took a postdoc at the National Radio Astronomy Observatory in Charlottesville, VA, I was still interested in this stuff because it was so bizarre. And they offered a summer student, and I took a summer student. I didn't know anything about her. Her name was Judy Rubin. Rubin. And I had her working on these flat rotation curves. Now that was in 1972. 

De Swart:

Yeah.

Shostak:

And so, she was doing something about it, and then she left. She was only there for a couple of months, and then she left. But two years later, her mother starting publishing flat rotation curves, actually. Her mother is Vera Rubin, or was.

De Swart:

Yeah.

Shostak:

Both dead now.

De Swart:

Yeah.

Shostak:

And so today, you pick up any textbook, they'll tell you that Vera Rubin was the one that found the flat rotation curves for galaxies, dark matter, and all that. But in fact, this was the story as I saw it. We had found it in our work at Caltech in 1968 and then I put Judy Rubin to work on it in 1972. So, I don't know, I assume that Judy Rubin talked to her mother and said, "Hey, by the way, this is what I'm working on and it's kind of interesting and whatever." But I wasn't there for that, so you can't ask Judy anymore and you can't ask Vera Rubin anymore.

De Swart:

No, no, definitely. Oh, that's fascinating.

Shostak:

That's fun. Yeah, and in fact, Albert Bosman, have you talked to Bosman?

De Swart:

Yes, I did talk with him. That's some years ago, but yes.

Shostak:

Yeah, yeah, he was in Groningen when I was there, as a student. And we actually did a few things together. He certainly was very helpful to me. He showed me how to use the equipment there to reduce data from Westerbork and so he was very methodical. And then he did a bunch, because this was so interesting that people started measuring the rotation curves using Westerbork. And he did a lot of that work. He wasn't the only one. Kor Begeman did it and there were others. Renzo Sancisi. But it had all been established by then, so.

De Swart:

Yeah. And so, going back, how did it start to establish? So, was it something that people generally did when you were doing your graduate? Like making rotation curves?

Shostak:

No! Nobody had ever done it before. Well, that's not quite true. That's not quite true. People had, there had been two kinds of efforts before we did what we did. We were able to do the rotation curve because we were doing radiosynthesis, right? We were able to have resolution of either two or four minutes of arc, depending on which galaxy you're talking about. It was all a matter of how much time you wanted to spend at the telescope.

De Swart:

And was that the—

Shostak:

Now the two or four minutes—

De Swart:

Sorry, go ahead.

Shostak:

Sorry.

De Swart:

Oh yeah, I was wondering, the resolution, was that top of the bill or the newest, the best you could get at the time?

Shostak:

Yes, it was. Because two minutes of arc corresponded to an 800-foot…so what is that, it's like 250 meters or something. 800-foot baseline and that was the farthest you could get the antennas from one and another at the Owens Valley at the time. So, two minutes of arc—you know, with a 21cm, you couldn't go up in frequency because you wouldn't have the hydrogen line. So, that was the best you could do, and so we did that and most of the data I have is two minutes of arc. But it was good enough because these galaxies were like 30 minutes or even 60 minutes across, right? So, you had enough pixels to really get a rotation curve that was pretty good, actually, all the way out to the hydrogen, which was farther out than you would see in the optical, actually. So that was okay, you could do that. But nobody else had been doing it except there had been some optical rotation curves published by… what's his name? He was down at UC San Diego. Burbidge.

De Swart:

Yes.

Shostak:

Burbidge and his wife, Margaret. And they had done a whole bunch of galaxies' rotation curves. But the rotation curves only went out, you know, to the bulge or a little farther. Right? So, they never got to the part where the rotation curve becomes flat. They published probably a dozen papers of these rotation curves, but it was all the inner part of the galaxy. [Laughs] So, this was the first time you could go much farther than that. Now, when we showed some of these preliminary results to a guy by the name of Morton Roberts, at the National Radio Astronomy Observatory. I remember my advisor, a guy by the name of Dave Rogstad.

De Swart:

Yes, whom you published with.

Shostak:

We went to Charlottesville, and we showed them this stuff, and so he tried to get a rotation curve for Andromeda, M31, and he used the 300-foot telescope, which was still operational then, and the 300-foot telescope had a beam of 10 arc minutes. So, not very small, but you know, that's all it was, a single dish. So, that was the best he could do, but Andromeda on the other hand is a couple of degrees across.

De Swart:

Yeah.

Shostak:

So, you know, he could get something, and his results were kind of... not definitive, but it didn't matter. I mean, we'd already done these flat rotation curves, so he knew that it was probably a flat rotation curve there. But he had been doing it as well. So, he was also involved in the radio mapping of rotation curves. That was after we'd done it at Caltech, I have to say, but still.

De Swart:

Yeah, and so how did this program get started? So, was the Owens Valley already running when you started your PhD? Your graduate?

Shostak:

What was already running?

De Swart:

Owens Valley. The radio...?

Shostak:

Oh yeah, no, Owens Valley was definitely already running. Owens Valley, the interferometer there was built in the 1950s.

De Swart:

Yes.

Shostak:

‘50s. And so, it was running, but what happened when I was there was that they bought some new receivers, they were called para-amps. So, they're parametric amplifiers. And they were much better than the ones they had had up until that time. They were much more sensitive. That allowed you to really do this, to actually map out galaxies, yeah.

De Swart:

And so that's where the research program started? Like the mapping out of galaxies started with…?

Shostak:

Yeah. Yeah, yeah, I think that's fair to say. Certainly, in the 21cm line, yes. Now, again, there have been single dish efforts. The Australians in particular used their antenna, the Parkes antenna. And they mapped some big galaxies in the Southern Hemisphere. But you know the big ones in the Southern Hemisphere tend to be the Magellanic Clouds. And those are irregular galaxies, actually. So, their rotation curves are kind of unclear. The motions are very messy. And in fact, we even analyzed the mapping they had done of two southern galaxies, NGC-300 and NGC-5236. They had published their data and Dave Rogstad had me look at it. And also, one of my thesis advisors was Maarten Schmidt, actually. Yeah. A Nederlander.

De Swart:

Yeah.

Shostak:

And you know, so we looked at those data, and we thought that there was something funny with the rotation field even then. But the fact that the rotation curves were flat didn't really become clear until we had mapped them with our interferometer rig.

De Swart:

And is that the Freeman papers? Was he in Australia?

Shostak:

Freeman, you mean Ken Freeman?

De Swart:

Yeah.

Shostak:

Yeah, Ken Freeman was actually in Groningen for a while.

De Swart:

Oh.

Shostak:

Yeah, he was there for I think two years when I was there? I was there a long time. But here was there for I think two years, and he was sort of marginally interested in this stuff. I don't remember him getting very involved at the beginning, but I may have forgotten. What I recall him doing at the time was he was interested in these funny ring galaxies, I think. Circinus galaxy, whatever. And he had a theory about how these things were formed, but then along came this guy, Alar Toomre, and he said, "Well actually, the way they're formed is you have one galaxy barrel through another galaxy to collision." And you end up with a ring. I had met Toomre at Caltech and he was the one that suggested that maybe these galaxies aren't really funny rotation curves, maybe there are expanding motions there. So, I tried that and it kind of fit the data, actually. But it wasn't very physical. But Toomre had worked out that, he thought he understood the ring galaxies, and I do recall the colloquium he gave at Groningen. And Ken Freeman, who was sitting next to me, he said, "Well, that's the end of my idea." [Laughs] But that kind of ended his idea about what causes ring galaxies. But in any case.

De Swart:

Oh yeah, so I met Alar Toomre, and I interviewed him on the subject, which was fascinating also. He still has his own ideas of this. And specifically on the galactic dynamics in the ‘60s. It's very, very interesting. So, how would you call... if I understood correctly, within radio astronomy people knew a lot about who was doing what? Is that correct?

Shostak:

Well, I don't know. I mean that's kind of hard to say, because you only know what you know, right? You certainly don't know what the radio astronomers were doing that you didn't know, right? And so, I obviously knew what was going on at NRAO, and I knew what was going on in Groningen. And there weren't too many radio astronomers at the time in Leiden or Nijmegen or any of those. I mean, and I think I knew what was happening in the field that I was doing stuff in. I mean, clearly that. 

As far as Ken Freeman goes, he wasn't there forever. He left after a couple of years. And so, I didn't really know what he was doing after that. After he left. But that would have been the mid-‘70s, maybe the late ‘70s, somewhere in there.

De Swart:

Ah yeah. And so, for this flatness, you mentioned that already in the late ‘60s, this started to pop up in the things that you were studying. So, can you tell me maybe a little bit more about how this started to become problematic?

Shostak:

Well, it became problematic right away. Because one of my thesis advisors, and I think it was Maarten Schmidt, he was very... sort of pressing. He was trying to look ahead a little bit. And he said, "So, Seth, you're going to map these galaxies, and what do you expect to find? Do you have any idea, so you'll know if you find something that you don't expect to find?" [Laughs] And so you know, consider I made models of what the galaxy would look like, and in particular, I made models of what they would look like, given the kind of rotation curves that we expected. And they were what are called Brandt curves. Because it was this guy, Brandt… I've forgotten his first name. He had published papers about the sort of model rotation curves. But they all assumed... I mean, none of them thought that there was anything like dark matter. They just assumed that the galaxy had a certain matter distribution. They were more massive in the middle and less massive farther out. And so, the rotation curve would go up and then it would turn over and then it would go down as one over the square root of r. Right? The way you'd expect for Keplerian. Right? And so, all the curves were variations of that. So, I was making all these model galaxies assuming that rotation curve. That kind of rotation curve. Right? And in my thesis, I think there's quite a bit of mention of Brandt curves or something. But, of course, as we'd say, when I was reducing the data, they didn't fit the Brandt curves at all. So, clearly something was wrong. All you could say was that there's an awful lot of mass somehow in the outer regions of these galaxies. 

De Swart:

And with whom did you share that? Was that quite known amongst the other people at Caltech?

Shostak:

Well, I don't know. I certainly gave a colloquium about it. And it's in my thesis and all that stuff. We, Rogstad and I, started publishing papers beginning in 1972 or 1973, I don't remember exactly when they came out. In Astronomy & Astrophysics, I think. I think that was where we published…

De Swart:

Yeah, I've seen those, yes. Indeed.

Shostak:

Yeah. Anyhow, so I don't remember the dates. I probably should, but it was shortly after I left Caltech. Within two years, because that's how long I spent in Charlottesville. So, yeah, we began doing that, but as we say, it was still a puzzle in 1972, in the summer of 1972. Because that's when I had Judy Rubin work on this and see if she could understand anything more. I don't remember what she did. It wasn't anything very dramatic.

De Swart:

But that was your, so that was a summer student? She would have been a graduate or even an undergrad?

Shostak:

Yeah, I think she may have even been an undergrad, but you can look up, see what date she was born, and this was the summer of 1972, that's for sure. So, you can figure out how old she was and that'll tell you.

De Swart:

That's interesting.

Shostak:

I think I can find it right here; I don't know.

De Swart:

That's interesting. And then so when did this start to get picked up also? Like for you it was problematic. For how many more people was it problematic at that time? 

Shostak:

Yeah, I'm just thinking, in 1957, so in ‘58... that would make her 66. She would have been ‘61, and in ‘72 she was 25. So, 25 years old and I guess she must have been a grad student, I don't know.

De Swart:

Yeah, I guess. Yeah.

Shostak:

Anyhow. Yeah, I'm sorry, so your question was, did other people know about it? Were there other people doing it?

De Swart:

Yeah, so how did people get this, indeed, for whom was it also problematic and how did it start to spread, that people started to understand that something was going on? 

Shostak:

Well, I think it's fair enough to say that Vera Rubin certainly made a big deal out of it. And you have to give her credit for that. We didn't make such a big deal out of it. Yeah, so that would have been the early 1970s. I don't know when Vera Rubin published her papers, but I have the feeling it was like ‘74 or ‘75, something like that. And you know, that was 3-4 years after I had graduated, and 5 or 6 after we had done the data, made the observations. So, somewhere around there, but I don't really know, because then I took a job in a completely different field for a while.

De Swart:

And so how about the colloquiums you were giving? Were you showing the velocity curves? And...

Shostak:

Oh yeah.

De Swart:

Yeah. And was it a conclusion you were drawing that there should be extra mass?

Shostak:

Wait a minute, I got the wrong Judy Rubin. Hold it. I got an art therapist by the name of Judy Rubin. Wait. [Laughs] Hold on, I don't want to give you the wrong... maybe she was an undergraduate. Hold it. Judy Rubin, there are so many obituaries. Judy Rubin, born 1952. So, in '72 she would have been, yes, she would have been 20 years old. Okay. Sorry, she was an undergrad.

De Swart:

Yeah.

Shostak:

Yeah, I had the wrong Judy Rubin. Harvard, University of Minnesota. There you go.

De Swart:

Interesting, very fascinating. And so how actually was Caltech during your graduate? Were the radio astronomers speaking with all the other astronomers? How was this...

Shostak:

Yeah, we were all in one building. There weren't too many radio astronomers at that time, I mean there might have been five. [Laughs] I don't think there were that many. Maybe five. And of course we were in the building with the other astronomers, so we certainly saw one another all the time. The head of the department, when I was there, was a guy by the name of Jesse Greenstein.

De Swart:

Yes.

Shostak:

And I certainly talked with him a lot. And people like Fritz Zwicky was still alive, so he would be at parties. But I was just a dumb student. I mean, that's...

De Swart:

[Laughs] Fair enough. And what was the status of radio astronomy, more generally?

Shostak:

Well, radio astronomy was on the uprise. It was on the, what do we say? ‘Up the lift’ or something like that? Anyhow, or ‘in the lift’, I guess you'd say? I don't know. And I think the reason was that it was still early days. It was the 1960s when I got there, right? And you know, radio astronomy had only really begun 10 or 15 years earlier, so even though the instruments were not big, it was still the case that very little of the sky had been looked at with radio telescopes, and the consequence of that was every time you made an observation, you got something interesting. Something to publish. So, you know, there were people, most of them were working not on 21cm. I may have been the only one doing 21cm work aside from my advisor. But there were other people doing, you know, continuum observations of radio galaxies and things like that. That was the sexy topic, radio galaxies. 21cm gas, hydrogen gas, and galaxies was not considered very sexy.

De Swart:

[Laughs]

Shostak:

Even today, I kind of wonder if it's very sexy. [Laughs]

De Swart:

And Dave Rogstad, that was your supervisor? And was he doing the same?

Shostak:

Yes.

De Swart:

He was doing 21cm?

Shostak:

Yeah, yeah, yeah. After all, he was my thesis advisor, so he was doing the same thing. We were working together, and the other radio astronomer there was... well, Alan Moffet. Alan Moffet was a very, very clever guy, actually. Unfortunately, Alan Moffet died very young. And then there was also... Let's see, Alan Moffet and the head of the observatory was a guy by the name of Gordon Stanley. An Australian guy. Because the Australians were very instrumental, you might say, in getting the instrument to work. A lot of what was still in the Owens Valley was because of the work of the Australians. He was there. Who else was there? Let's see... Alan Moffet...Gordon Stanley. Marshall Cohen showed up there eventually, if you know Marshall Cohen. He's still at Caltech, I think.

De Swart:

Okay.

Shostak:

He's still busy. And I had three advisors. I had Rogstad, he's the guy I worked with all the time. But I also had Maarten Schmidt, and I saw him at least once a week. 

De Swart:

Oh.

Shostak:

And then the third guy was Alan Moffet.

De Swart:

And once a week? So, what would you discuss with Maarten Schmidt?

Shostak:

Well, mostly, we would talk about my thesis. They weren't long meetings. They were like 15-minute meetings. But he was, let's just say, quite keen to make sure that I had thought about what the data might mean. You know, that I might predict what we might find. I remember that, I thought that was very good of him.

De Swart:

Mm, yeah. And given that Fritz Zwicky was there, I would be interested, were you aware also of the problem that was going on in clusters of galaxies, like in this whole other field of extra-galactic astronomy?

Shostak:

Well, it was true that, I mean, see, that was Fritz Zwicky, best I could figure. And when I was a first-year graduate student, they gave me a desk down in the basement. In fact, it wasn't even the first basement, I think it was the second basement of the astronomy building itself. And I shared that with Zwicky’s medewerkers [assistants], right? [Laughs] Okay. And occasionally, you'd see Zwicky at the colloquia too. He didn't come in every day. And so, we knew about this, and I should say that Zwicky had the habit of... At every colloquium, when we finally got to the question and answer part of a colloquium, he would raise his hand and say, "Actually, I showed this in 1934." Right? So, all the other astronomers at the time, they were all kind of chuckling and, "Ah yeah, Fritz, we know you discovered everything." I have to say, you know, the facts of the matter are that he probably did do all that. I mean, Zwicky was a very big, clever guy. It may be that all of that was true that he was saying. But in any case, the fact that he had noticed that there was a problem with the virial theorem not working in clusters of galaxies, we knew that. We knew that. But you know, it was just an interesting result. I don't know that anybody was spending a lot of time talking about it.

De Swart:

Yeah. And so, when, for you, did these problems start to get connected?

Shostak:

Well, I don't know exactly when they got connected. I think that, you know, I don't trust my own memory on this. It was certainly the case that by the time I got to NRAO, you know, before I had Judy Rubin as a student, that it was clear that something was wrong. But we already knew that. And so, I'd spent quite a bit of time studying lots of late-type galaxies, but there was no instrument at NRAO that had high resolution, so it was on the basis of what are called the single-dish hydrogen profiles, if you will. So, you just get one spectrum for the whole galaxy. And I look at more than 100 galaxies in this way. And that was a lot of work back then. It wouldn't be so much work today, but it was then. And you could tell by looking at these profiles that all the hydrogen was powered up in the streams of the profile, and you know, I knew from making models, thanks to Maarten Schmidt, I have to say. I knew from making models that that was because they had flat rotation curves. So, knew even then that they all have flat rotation curves.

De Swart:

Okay.

Shostak:

And that was ‘73, ‘74, that's when we were doing that.

De Swart:

Okay, and then so if you see papers now, people often quote work by Ostriker and Peebles and Jaan Einasto in Estonia, connecting these things up. So, were you aware of these things when they came out?

Shostak:

No. Peebles, did you say? James Peebles?

De Swart:

Yeah.

Shostak:

No, I didn't know. You know, I went to Princeton as an undergrad, so I've met Peebles, but I never knew that he was involved in this. That I have to say. And as far as Einasto goes, my roommate in grad school was from Estonia, so he would talk about Einasto [Laughs]

De Swart:

Oh really?

Shostak:

But I don't remember him being involved either. I mean, all of that may have been later. Remember, this went to about 1974, ‘75 after that, I didn't do too much on flat rotation curves. I mean, by that point, everybody knew about it, and Bosman was mapping these things in many galaxies, Kor Begeman was doing something similar. and Renzo Sancisi. All these were people in Groningen. I think they were more involved than anybody else in the Netherlands. You know, but by then, I mapped a couple of more galaxies, the NGC 6503 and so forth and so on. M101 we did. Well, M101 we'd done at Caltech, actually. But I did some stuff with Pieter van der Kruit.

De Swart:

Oh, that's very interesting. Yeah, he's still in Groningen, right?

Shostak:

Yes, he is. And in fact, I think he was the dean or something. But in any case, yeah, Pieter and I did a bunch of face-on galaxies, NGC 628 and on. But Pieter was not interested in the rotation curves. They were all known that, flat rotation curves, so by this point everybody knew that. But he was interested in seeing if we could measure the dispersion, in other words, the vertical motions. Where that's what you would be, you know, by taking the rotation out, by looking at a face-on galaxy, then you could just see what is the dispersion, if you will. The 10-15km per second dispersion of the gas in the disk. It'd give you some idea of the thickness or in fact the densities, stellar density, in the disk of these galaxies. So, that was a different problem. But we used the Westerbork and did it. And then I did a bunch of stuff with Woody Allen. Woody Allen? Woody Sullivan. I didn't do much with Woody Allen.

De Swart:

[Laughs]

Shostak:

Like to have worked with Woody Allen. But Woody Sullivan and I synthesized Stephan's Quintet, because there was a big controversy then about whether all the red shifts were really red shifts, or whether they were due to some strange cosmological phenomenon. This was the idea of a guy by the name of Chip Arp.

De Swart:

Oh yes.

Shostak:

Halton Arp was his name. You may know about Arp. 

De Swart:

Yeah.

Shostak:

And I had known him at Caltech. He was a real snazzy dresser, Chip Arp was. Anyhow, so we were trying to find out whether these galaxies were really at great distances, or whether they were very close with high red shifts, because of something that, you know, some physics that we didn't know about. And different people were getting different results, but the results we got suggested that the Hubble law was right. So, we were doing that.

De Swart:

And so, you're saying this flatness at one point, people were aware that these rotation curves turned out flat, so then when did people start to be convinced that it should be mass that we're actually not seeing? And then what kind of mass should it be?

Shostak:

Yeah, I don't know the answer to that. I mean it was clear that there was mass. Nobody explained the rotation curves as doing anything other than mass. I remember in my colloquium in 1972, saying, "Yeah, there's something out there, but mass to luminosity ratio is very, very high. But you know, since it's not luminous, whatever this mass is, we don't know what it is." And I remember Jim Gunn asked a question too about that. You know, so it was clear that there was something going on, but we didn't know what it was. I don't know when people started saying "dark matter." I don't know about that, and I honestly don't know.

De Swart:

[over-emphasizing] "Dark Matter." Indeed. [Laughs]

Shostak:

Right.

De Swart:

So, that's interesting. And so how would you now reflect on how dark matter's history gets portrayed?

Shostak:

Yeah, I don't know, the only thing that I know is that, okay, if you pick up any astronomy textbook, they talk about dark matter of course. And so, part of it is the discovery of dark matter, and that's always, the credit is always given to Vera Rubin for that, you'll notice. That's always the case. But as you've heard here, that wasn't actually quite right. [Laughs] But what am I going to do? And you know, or what is Rogstad going to do? Rogstad's well aware of this too. And I think Bosman actually knew about it too. He said something about it. But anyhow, so there's that. But the other thing is, what is it? And that's the question that most people seem to be interested in primarily. Of course, they are. And so, just about every week, there's a story in the science literature about a new experiment—

De Swart:

[Laughs] Tell me about it.

Shostak:

Yeah, I haven't found this particle, I found that particle. [Laughs] Or you could talk to Bob Sanders, who's also still in Groningen.

De Swart:

Yes. Mm.

Shostak:

Maybe you already have, have you talked to—

De Swart:

No, I have not yet, and I'm very much, I would love to talk to him, and I will make sure that this will happen soon.

Shostak:

Well, he's great.

De Swart:

Yeah?

Shostak:

He's one of my best buddies ever. I knew him in Charlottesville. He was from Texas originally, by the way. He might try speaking Dutch to you, but he never spoke any Dutch when I was there.

De Swart:

[Laughs]

Shostak:

But yeah, Bob Sanders. But you know as you're, I'm sure, aware, Bob Sanders is very much into this idea that there is no dark matter, it's just that Newtonian physics doesn't work when you have…

De Swart:

Doesn't work, yeah. Indeed.

Shostak:

100,000 light years. And so, you know, Milgrom's ideas and so forth. And I think that almost everybody else in his department is skeptical that this is right, but that only makes me admire Bob more because he's willing to gamble the last, I don't know, at least 20 years on this idea. So, he's definitely worth talking to, and he's definitely worth talking to even if all you're talking about is women and wine. Because he's worth talking to.

De Swart:

[Laughs] Which I'm also good at, I guess. I should be. I'm still a graduate student, so. [Laughs]

Shostak:

Yeah, you can talk to Bob about anything and he's witty, he's clever. And he's a nice guy.

De Swart:

Amazing. Well, no, it's been fascinating. So, I also talked with Jim Gunn. I talked with Neta Bahcall. Was she still there when you were doing your graduate?

Shostak:

Neta Bahcall?

De Swart:

Yeah.

Shostak:

Well, I never knew really Neta Bahcall. I met her. But when I was a grad student, her husband, right, John Bahcall was at Caltech.

De Swart:

Oh yes.

Shostak:

So, I would see him in the computer room occasionally. We would talk a little bit. He would ask me questions that I didn't know the answers to. But at that point, he was working on, you know, I don't know if he was doing the neutrino stuff and he was doing something with high energy radio galaxies, stuff like that. So, it wasn't my field, and John Bahcall was a very, very bright guy, so even if he had been in my field, I don't think I could have answered his questions. [Laughs]

De Swart:

Yeah. And so, I also talked with Mort Roberts, I went to visit him in... Jacksonville? Is that correct?

Shostak:

I don't know where he is now. He was in Charlottesville when I knew him. 

De Swart:

Yeah, yeah, but he's not too far from NRAO still, I believe. But so, you were a postdoc, right, at NRAO when he was there?

Shostak:

That's correct.

De Swart:

Ah yes.

Shostak:

But I met him when I was still a grad student because we were showing him these rotation curves that we had mapped, yeah. I remember doing that with Dave Rogstad. We just showed him what we were doing, and we also, he was interpreting some of his data, mainly the 300-foot, in a very strange way. He thought that the galaxies, what was it? Yeah, oh I know what it was. He had these channel maps and he was interpreting these to tell him something about the distribution of hydrogen in the galaxy. And I remember he went to the bathroom or something and Dave Rogstad said to me, "He doesn't understand these maps because the fact that there's this funny dumbbell shape is because of the rotation, not because of the hydrogen distribution." Rogstad was right about that, of course. So, we did point that out to Mort, we did. Yeah.

De Swart:

Ah, that's interesting. And—

Shostak:

There are many interesting things I could I tell you about Mort Roberts, but they don't have much to do with rotation curves. [Laughs]

De Swart:

And so, for you, was it interesting to interpret these, the consequences of these rotation curves? You saw this extra mass, but did you do any guesses to what kind of stuff it would be? Or wasn't that part of the project?

Shostak:

No. No, well, I don't know, maybe you could say, you know, looking back that it should have been part of the project, but no, we didn't know what it was, and I didn't know enough to guess oh, maybe these are WIMPs and such like. But I just didn't know anything about that. So, we didn't, all we knew was that there was, you know, the galaxies are rotating in a completely different way than we thought they were going to.

De Swart:

Yeah. And the relation between the optical astronomers? How was that?

Shostak:

Yeah, well there, obviously, I had some dealings with optical astronomers, in terms of my thesis work, you know, they would take photos of the galaxies that we were studying. And in one case, the irregular galaxy I studied, IC 10. They even made a rotation curve, actually, because it was so small, they could do that. I think they used the... Oh no, wait a minute. They didn't have a rotation curve. What they did was they mapped the H alpha in that galaxy. So, they knew where the hot hydrogen was. And so, in my thesis, you could compare the hot hydrogen to the 21cm cold hydrogen. So, there was some collaboration there. Not a whole lot, and they weren't doing anything on rotation curves when I was there. That was, the only rotation curve work while I was a grad student was the Burbidges, down at UC San Diego. 

De Swart:

Oh yeah. And in terms of Vera Rubin, did you match before she started working on this?

Shostak:

I'm unsure of that. I certainly had met her more than once, because she was at, let's see, the Carnegie Mellon. Did I get this right?

De Swart:

Yeah.

Shostak:

The Carnegie—no, sorry, not Carnegie Mellon, Carnegie Institute of Washington.

De Swart:

Oh yes.

Shostak:

In fact. In D.C. And I grew up in the D.C. area, so I actually went up there and I think I was maybe auditioning for a job. I'm not sure anymore, but I had certainly met her more than once before. At least once before she published any of this stuff. But I don't remember exactly how often. I met her and I met her husband. I didn't meet her daughter until her daughter was suddenly my student.

De Swart:

Ah yes. [Laughs] Yeah that's an amazing story, actually. Okay very interesting, yeah, and so for how long were you yourself still doing these kind of things in radio astronomy?

Shostak:

Well, let's see. What happened to me after... So when I left Groningen, and that was 1988. I moved back to California... Well, not really "back," I moved to California. And then I was doing something, I was in a software startup with one of my brothers. We'd been doing computer animation in Groningen too using the astronomy department's computer. That was a whole ‘nother story. We were part of what was called Science Park, which was an initiative to turn part of Groningen into the Silicone Valley.

De Swart:

Ah, look at that.

Shostak:

But without the good restaurants, I've got to tell you. [Laughs] But in any case, when I left there, I think, to this part of California, was in a software startup, and when that bombed out, which it did, I did other things for a while, and it's very interesting to be unemployed in the United States. Because in Holland, if you lose your job, the government continues to pay you.

De Swart:

Yes.

Shostak:

Like 80% of what you were earning or something. You know, so it's not a problem. But if you move to California and lose your job, well, you might just be on the streets asking people for money. So, I tried to do anything I could to make money—but then, some people at the SETI Institute found out that I was here in the area, and they called me up one day and they said, "Do you want a job?" So, that's when I started working for SETI. It was about two years after I came back to California.

De Swart:

Awesome. And you were already doing outreach before that? They knew what you were doing?

Shostak:

Yeah, well, they hired me actually to do SETI stuff, which I also do, but mostly I do outreach stuff. And mostly writing. You know, a lot of writing. And radio show and all that stuff. But yeah, no, I was part of the SETI team because I knew interferometry, obviously, and that sort of thing. But yeah, no, I was doing outreach in Groningen, for that matter. I was on a lot of TV shows, and I did some of the special effects for Teleac, if that still exists. I don't know if Teleac—

De Swart:

Teleac! Oh yeah, I'm not sure, but I used to watch that as a kid, so I'm not sure if it still exists.

Shostak:

Yeah, well, there was a series being produced at that time, called Moderne Sterrekunde [Modern Astronomy].

De Swart:

Moderne Sterrekunde. Oh yeah.

Shostak:

Yeah, Moderne Sterrekunde. And the host was Roel Gathier, that was his name.

De Swart:

Okay.

Shostak:

Roel Gathier, and he was a student. He was a student, I think a grad student actually. I think he worked on planetary nebulae or something. But he was a grad student in Groningen, and he was the presenter, but they asked me to do a lot of the special effects, so I made those in the basement of my flat in Groningen.

De Swart:

[Laughs] Okay wow. And was that the start, or were you earlier in this...?

Shostak:

Are you still there?

De Swart:

Yes, indeed. Was that the start of the kind of outreach things that you were doing?

Shostak:

I don't think so. I don't know. Even when I was in Groningen, even before I was in Groningen, I was you know writing articles, popular articles, giving a lot of, well not a lot, but giving talks. And in fact, when I was in Charlottesville at NRAO, we made the movie that was used for the visitors to Green Bank.

De Swart:

Oh.

Shostak:

It's called “The Invisible Universe”, yeah, with dancing telescopes and stuff like that. Yeah no, I made that with my roommates.

De Swart:

Very nice.

Shostak:

Yeah, I've made films since the age of 11, so that wasn't anything new.

De Swart:

And so, in Groningen, you were there for one year in 1988?

Shostak:

No, I was there for 13 years.

De Swart:

Oh yeah, yeah. 

Shostak:

I got there in 1975 and then left in 1988.

De Swart:

Oh yes, sorry, so I misunderstood that. 

Shostak:

By the way, have you talked to Marshall Cohen?

De Swart:

Nope.

Shostak:

Do you know of him?

De Swart:

Nope.

Shostak:

Okay. He's at Caltech, or at least was the last time I knew. He used to come up here actually and we'd have dinner. Marshall Cohen. Caltech hired him when I was a student there, so it was probably around 1968 or somewhere around there. I don't know exactly. A radio astronomer, really nice guy. And he wrote a history of the Caltech interferometer.

De Swart:

Oh, that's interesting.

Shostak:

Yeah, so that might be useful to you, if you can track him down. Marshall Cohen, yeah.

De Swart:

That's a very good advice, thank you very much.

Shostak:

Well, if you actually get ahold of him, say, "boo" from me. "Hoy" or something.

De Swart:

Hoy, yeah, I will say hoy. [Laughs] And I will do the same if I will meet Bob Sanders.

Shostak:

Yes, please. Sanders is, you know, just kick him in the shins or something for me.

De Swart:

[Laughs] I'm not sure, yeah, there's still a heated debate in the MOND/WIMP regime, so actually I have two supervisors here, one of them emailed you, he's Gianfranco Bertone. He's very fond of the WIMP and he's a hotshot in the dark matter physics. And I have a history super—

Shostak:

Sorry, what's his name again?

De Swart:

Gianfranco Bertone. Bertone.

Shostak:

Bertone. Sounds like I know him, but I can't... I don't know. There were numerous Italians, actually, in Groningen at the time.

De Swart:

Sancisi was one of them.

Shostak:

The astronomy department, the nationality with the fewest representatives was probably Dutch. [Laughs] They were all foreigners. You know, in those days, it was probably still true. If somebody came from Leiden to give a colloquium, you know, like Harry van der Laan or something, they wouldn't give it in Dutch. They gave it in English, always. There were so many foreigners in Groningen.

De Swart:

And oh yeah, so Sancisi was one of the Italians, right?

Shostak:

Yes.

De Swart:

So, oh yeah, I was telling, so I have the Italian supervisor, but another supervisor of me, so there are three, is Erik Verlinde, who is a theoretical physicist.

Shostak:

Yes.

De Swart:

And he actually has his own idea of, like, a MONDian idea of alternative gravity. So, they fight on Twitter about this.

Shostak:

I see.

De Swart:

[Laughs] Which is an interesting dynamic, having them as supervisors.

Shostak:

Well this is… American politics is fought on Twitter. 

De Swart:

Yeah. [Laughs] That's also fascinating. Which could also be a PhD thesis on that. [Laughs] 

Shostak:

It's terrible.

De Swart:

But okay, thank you very much. This has been very valuable.

Shostak:

Well listen, I don't know if it has been or not, but don't hesitate. You have my email address, of course, so don't hesitate to get in touch. Always happy to talk to somebody that's trying to [speaking in Dutch] or whatever they call it.

De Swart:

[speaking in Dutch] That sounds quite okay. Thank you very much for your time.

Shostak:

Okay, good luck.

De Swart:

Thanks, cheers.

Shostak:

Bye. Dag.

De Swart:

Dag. [Laughs]