22 minute read
Vera Rubin, Pioneer
ASHLEY JEAN YEAGER: Astronomer Vera Rubin’s Galactic Vision
TOLD TIME AFTER TIME SHE NEEDED MORE DATA
to back up her bold ideas about the universe, pioneering astronomer Vera Rubin got the data that helped establish the reality that we live in a universe with more dark matter than luminous matter. From the August 26, 2021, Humanities Member-Led Forum program “Bright Galaxies, Dark Matter, and Beyond,” part of our Good Lit series, underwritten by the Bernard Osher Foundation. ASHLEY JEAN YEAGER, Associate News Editor, Science News; Author, Bright Galaxies, Dark Matter, and Beyond: The Life of Astronomer Vera Rubin In Conversation with GEORGE HAMMOND, Author, Conversations With Socrates
GEORGE HAMMOND: I’d like to welcome Ashley Jean Yeager, a science writer and the author of Bright Galaxies, Dark Matter, and Beyond. It’s the story of the life of astronomer Vera Rubin. Let’s talk to Ashley about this very interesting story about a female astronomer from the 20th century who was one of the first scientists who supported the idea of dark matter. Ashley, first, welcome to The Commonwealth Club. Great book. Wonderful job. ASHLEY JEAN YEAGER: Thank you so much for having me. I’m so excited and honored to be here. HAMMOND: Let’s start with a little bit of background about Vera. We have this woman fighting against the old boys club, basically, to make progress. Very successful at it. Let’s just give an idea about the span of her life. She only passed away a few years ago in her 80s, but really got active early on. Maybe we can set up how she did this. YEAGER: Yeah. Vera Rubin was born in the 1920s. She grew up mostly in Washington, D.C. At the age of about 10, I guess, she was sharing a room with her sister. There was [this] row of windows in their bedroom, and she just became fascinated by the stars. She would spend every night looking out the window, watching the stars, tracing their paths across the night sky. While she was doing this, she was trying to read about scientists, Benjamin Franklin, Isaac Newton, and she also came across the story of Maria Mitchell, who really put professional astronomy on the map for the United States. Maria Mitchell discovered a comet with a telescope, and because of that was awarded a medal from the king of Denmark, and then went on to found an observatory at Vassar College. Vera learned about all of these different stories, and then eventually ended up at Vassar to study astronomy.
Far left: Science journalist Ashley Jean Yeager, (Photo by Chris Johns.) Near left: Cover of Yeager’s biography of Vera Rubin. Top: George Hammond on the Club’s Taube Family Auditorium stage interviewing Yeager. Above: Yeager makes a point about the development of deep space science.
HAMMOND: One thing that’s important about [studying] astronomy at Vassar—how big was the department? YEAGER: She was the only student in the department. This is the 1940s, just after World War II had ended, and she was the only astronomy major at the time. HAMMOND: But they had a little observatory and a professor. That’s not too bad. YEAGER: They did. They had a little observatory, and that was actually where she got some of her first hands-on experience going out and making photographic plates of the night sky and different objects in the night sky. I think [that’s] where she really learned to love to do it and going through that process of making those observations. About the same time, she ended up meeting Robert Rubin, who became her husband. He was a graduate student at Cornell at the time, and as Vera was thinking about what her next steps were, she had applied to Harvard [and] several other universities to do her graduate work in astronomy, and ultimately decided to go to Cornell with Bob.
I think this is something that was a really fundamental decision that in some ways put her on the path to being this luminary in astronomy, because she was able to ask questions as a graduate student that maybe she wouldn’t have been encouraged to ask at a place like Harvard or Princeton. She had that intellectual or creative freedom to dig into something very different than a traditional question. Actually, the question she asked was, Does the universe rotate? Which is something that’s incredible to think about, and her logic made sense. It was something that George Gamow, one of the big name cosmologists at the time, had posited. The idea was [that] everything rotates, right? Planets rotate around, they orbit the sun, stars orbit a galaxy. Why wouldn’t galaxies orbit a center point in the universe? She really went after that question and tried to collect data to find an answer. She did find some unexplained— HAMMOND: It’s pretty bold to think that you can get any data to support an answer on that. Right? YEAGER: Right. Yes, exactly. Especially at that time. This is late 1940s now. You’re just starting to have these galaxy surveys, where you’re starting to see threads of long tendrils of galaxies, some of the beginnings of the large-scale structure of the universe starting to emerge. Yeah, she was trying to get the different velocities of galaxies as they move through the universe to look for this universal rotation. She did find some strange, unusual, unexplainable behavior, and she presented that at one of the big astronomy meetings and got the reaction that no one really believed her. They were like, “No, this can’t be right. You don’t have the data to make this claim. You need to go back and do more work.” I think that really stuck with her as a criticism. Like, okay, I constantly will need more data to confirm whatever conclusion I draw. You have to remember, at this time, she wasn’t able to go to the telescope herself. There were no facilities that were open to women in the late ’40s, early 1950s. HAMMOND: Just out of habit that they didn’t do it or were there so very few astronomers that were women? Is there anything in the basis for why that was true so late? Because it’s fairly late, in the ’40s and ’50s, to say women can go and look into that. Or was it just a habit, like in accounting or something like that, where there were so few women as well? YEAGER: I think you could say that, but then there are also arguments that there weren’t really facilities for women. One of the famous stories for Vera is about this bathroom at Palomar Observatory, and how, essentially, the application said women can’t apply because we don’t have the facilities
Above: At the NASA Sponsors Women in Astronomy and Space Science 2009 Conference, left to right are Anne Kinney of NASA Goddard Space Flight Center, Vera Rubin of the Department of Terrestrial Magnetism, Nancy Grace Roman of NASA Goddard, Kerri Cahoy of NASA Ames Research Center, and Randi Ludwig of the University of Texas, Austin. (Photo by NASA.) Right: Vera Rubin with John Glenn. (Photo by Jeremy Keith.)
to accommodate women. That segmented everything just for men. HAMMOND: All they needed was an allgender bathroom, and everything would have been fine? YEAGER: Exactly. Vera would later make that point. HAMMOND: It’s just a funny thing that people use as a block to stop something from happening, basically. YEAGER: Yes, yes. Absolutely. HAMMOND: Sorry to interrupt the story, but [what stopped her is] a very interesting part of the story. Apparently, tiny little things. YEAGER: Yeah. She actually had this memory of going to Lowell Observatory when she was a graduate student, and she saw these male astronomers making observations and publishing all these papers, and it made her feel inadequate. It made her really question, They’re so far ahead of me, can I actually do this given the limitations that I have? That was always a question in the back of her mind, and for some reason, she pushed forward and kept trying to challenge it. I think a lot of that was from support from her husband. He very much wanted her to have a career and made a lot of decisions to make that possible for her. HAMMOND: She breaks through eventually. Each step of the way, it’s basically that she does something fairly outstanding and makes a presentation, and each time there’s more data, it’s more convincing, it’s a little bit more reliable. People are going to use the fact she’s a woman doing this, right? YEAGER: Yeah. HAMMOND: Eventually, she breaks through. But it takes how long before she actually gets time on [telescopes]? YEAGER: She really wasn’t able to go and observe until the early 1960s. I think that was the beginning, and I think she really coveted being at the telescope, because it was so sacred, almost. What happens is that Kitt Peak National Observatory in Arizona opens. When it does open, it’s open to women, so she applies for time there. Around the same time, her husband has the opportunity to go on sabbatical and picks to go to La Jolla, California. Margaret and Geoffrey Burbidge are there, and they’re world-renowned astronomers at this point, mainly for their contribution to understanding how stars make their energy. Vera asks them if she can work with them, and that’s another opportunity to go to the telescope with them.
She gains more skills, and that’s when she really starts working on the question that will become her central thesis that gets us to the point of understanding that the universe is made of stuff that we still don’t understand. What happens is Geoffrey and Margaret Burbidge are looking at galaxies and how stars orbit the galaxy, what speed they have going around the center of the galaxy. They’re looking mainly at stars close in to the center of the galaxy and recording those speeds. The assumption is, at that time, that they’re only going to look at stars a certain distance from the center of the galaxy because, just like in the solar system, the speeds of stars farther out will drop off, and that is just what everyone assumed, it was written in papers over and over again, and no one really said, “Hey, let’s try to find stars farther out from the center of the galaxy.” HAMMOND: The example was that the solar system, the planets, due to the speeds, do drop off. YEAGER: Yes. HAMMOND: It’s a really big issue. Why don’t you describe what it is? In the case of the solar system, there’s a central sun, and then there’s the planets going around it. Everyone’s familiar with crack the whip, for example, this game. Of course, the outside person ends up going faster than they possibly can and goes flying off. There is something like that going on in a solar system, and they assumed it would be true for galaxies. That’s the basis for their assumption, and it’s easier to do the stars closer, and so that’s all they did. But Vera said, “Let’s look at this differently.”
Go ahead. I’m sorry. YEAGER: Oh, no, no. That was a great explanation. HAMMOND: Why is it that in the solar system, not live, but in the solar system, when the planets go around, they go at different speeds? YEAGER: Yeah. Pluto is very, very far from the sun, and so the gravity on it is not as great, and so it just plods along. While if you look at Mercury, Mercury’s very close in, and it’s just whipping around the sun super fast. It’s basically what’s pulling on those planets and just the difference in the amount of gravity that you have to affect those speeds. HAMMOND: But in the galaxies, the central core—whatever it is, some people think black holes, some people think other things—of a spinning galaxy is only a small percentage of all the mass in the galaxy. Whereas in the solar system, our sun is something like over 99 percent of the mass in the solar system, and therefore, that might be part of the picture too. YEAGER: Yes. Absolutely. HAMMOND: Everyone made this assumption, that the galaxies would behave the way the solar system did, and Vera wasn’t so sure. This is her big contribution into the dark matter thing. YEAGER: Yes.
After that, after asking that question about whether the universe spins, she really got into how an individual galaxy spins. That’s how she gets to this point of looking at these different stars to understand how are galaxies put together. She starts to question this assumption, and really with her students at Georgetown, because she did her Ph.D. at Georgetown and then ended up staying on as faculty there and took on some students, and they actually helped her first start to ask this question about the Milky Way, our own galaxy. Really trying to find stars very, very far from the center of the galaxy, and much farther than where the sun sits from the center of the galaxy, and try to understand, Do these stars move quickly? Do they move more slowly? Do they plod along? Our galaxy’s hard to work with, because we’re inside of it. It makes it very hard to get a sense of what’s going on. HAMMOND: I thought that was a very interesting part of your story, that people were much more confused about the Milky Way and trying to figure out what’s going on, than [a galaxy that’s] much more distant because you can look at it from the outside. They learned much more about galaxies from the further-away galaxies, and then applied it to the Milky Way and tried to figure out if it’s true here. YEAGER: Yeah, absolutely. She’s asking this question, she’s working with our students, and also had been influenced by the Burbidges. She gets to this point where she’s juggling a lot of different things. She’s juggling teaching, she’s juggling going to the observatory and doing her research, her family, trying to figure out how to navigate departmental politics. She gets to a point that she feels like, okay, something’s got to give here. She decides that the thing that she would want to give up is teaching. She goes and asks for a job at the Department of Terrestrial Magnetism, which is part of the Carnegie Institute. There are researchers there who are asking the same question about galaxies, and they’re working in radio astronomy, radio wavelengths. Obviously, she’s working in the visible wavelengths, what we can see.
After some deliberation, they finally do decide to hire her. She’s the first female staff scientist at the department, and that leads for some interesting onboarding practices which happened to happen on April Fool’s Day, April 1st. She shows up, and they have no paperwork for her. At first, they think she’s a secretary, and she has to claim, “No, I’m a staff scientist.” What was really interesting, and I think, again, a crucial moment in her career, is the director at the time had set up two offices for her. He had set up one office with one of the radio astronomers, and then he had set up another office for her with this very gifted instrumentalist, Kent Ford, who was creating this device that essentially would take photons from very faint objects and magnify them so that you could see stars very, very far away, which became key to Vera’s work.
She moved in with Kent Ford. He told me, many decades later, that she just never moved out. This started the beginning of their collaboration. What she did with him is she used this instrument that he had to look for very faint stars in our neighboring galaxy, Andromeda, and start to track the speeds of those stars as they orbited the galaxy. This was late 1960s. She starts to notice something very odd, even in some of the first observations that they make, that those stars far out aren’t doing what they’re supposed to be doing. They’re moving way too fast, if you were using the assumption that the galaxy would work like a solar system.
This starts to get into the meat of Vera’s work. . . . If you were following that solar system assumption, what you would think that you would see is . . . the stars really far out going really, really slow around the center of the galaxy. But what Vera started to observe is that that didn’t happen. The speeds didn’t drop off. Those stars really far out are zooming around the galaxy at roughly the same speeds as stars much closer in. HAMMOND: You talk about in your book, when we think about galaxies, we’re thinking about the central thing with the cloud of stars around it. But you’re saying that every galaxy is actually a big spherical halo that goes this far out. Galaxies, in addition to solar systems, have a central core, and at the core of the galaxy is even a deeper core, but then all the stars that we see, that’s still pretty much the center of the galaxy, and that the galaxy is surrounded by stuff for hundreds of millions of light years around it, or whatever, that are still in its orbit. YEAGER: Yes, absolutely.
This starts to get to this question that she and others were stumbling on in the late 1960s, early 1970s, that you have these objects really, really far out, farther than where you can see the galaxy, and they are moving way faster than astronomers would have expected. People start to question, “What’s going on here? Why are these objects super far out moving so fast?” What they’re starting to think about is, Okay, if this data is true, if these numbers are true, then something out there has to be pulling on those stars, something has to be revving them up, just pulling them along, making them go super, super fast. Otherwise, they wouldn’t be able to stay in the galaxy. They would just be flying off into space. At about this time, you have theorists [who] see these observations, they see some other observations about galaxies and clusters also moving rather quickly.
There comes this point where researchers start talking about dark matter. In reality, dark matter the term was really coined in the early 20th century as researchers were looking at individual galaxies and also these clusters of galaxies. They had this sense that things weren’t operating the way astronomers had assumed. That there might be something else out there, whether it’s stars that we can’t yet detect, whether it’s something unknown that we don’t know, but there might be this stuff that’s pulling everything along, making things move fast, or making galaxies interact in ways that we don’t understand. HAMMOND: At the beginning, it sounded like from what you wrote, the assumption was that it was more like the matter of dead stars, old planets, the equivalent of asteroid belts. That kind of thing. But you don’t really see these things, because what you see is the light. Luminous matter is one thing, [and there’s] non-luminous matter.
It got more mysterious as time went on? YEAGER: It got more mysterious as time went on. That’s right. You had these rumblings about dark matter in the 1920s, 1930s, but no one who really took it seriously, unfortunately. People just thought, Oh, how can the universe be made of stuff we can’t see? Those observations must be wrong. Really, when we returned to this question in the 1970s, she got the same reaction. There were some theorists who were starting to piece together that maybe galaxies had more matter, that maybe they had this spherical halo that encompass them. But it wasn’t a mainstream idea yet. You had all these different pieces to suggest that the universe was playing these tricks on us, but not everyone was on solid ground that this was really happening. What happens is Vera publishes these results, she gets some pushback from people saying, “Oh, well, that’s just Andromeda. That’s just our neighbor. Maybe it’s an outlier.”
—ASHLEY JEAN YEAGER
HAMMOND: You need more data. YEAGER: Yeah, you need more data. You really have to do this in other galaxies. To which she says, “Fine, I will go do that,” and she does. [In the] late 1970s, she’s starting to put this observing program together. You have to remember, this is really hard. You’re looking for stars and galaxies very, very far away. You’re trying to measure how quickly they move around that galaxy, and you can’t use one or two stars. You have to have several stars in that galaxy. It’s a tall order, but she just becomes determined that she will do it. She starts to do this in galaxy after galaxy. At first, she has five galaxies where she sees the same pattern.
Essentially, you see the same thing. The speed starts to go up, and then in the most part, they level off. Meaning those stars, again, very far out are traveling much faster than what you would expect if you’re using that assumption of Newtonian gravity and the idea of the model of the solar system. What she’s showing is there are smaller galaxies, there are mid-sized galaxies. Then [there’s] one called UGC 2885, and that is one of the largest spiral galaxies in the universe, and you have that same pattern. [UGC 2885] is massively wide, and even very, very far out at the edge of that galaxy, those stars are still moving super fast. This paper with this data came out in early 1980. At this point, there had been the theoretical work, there had been two astronomers who had written a review article saying we need to take the idea of dark matter seriously. Then I think with Vera coming along and saying this isn’t just something that we see in one or two galaxies, this is something that we see in 20, 30, 40, maybe even 100 galaxies. I think the astronomy community had to take a step back and say, “Okay, we really need to take this issue seriously. We really need to start thinking about what these data are telling us and how it’s going to reshape what we think about the universe.”
Because essentially what all of this is telling us is that most of the matter that we’ve been looking at, this luminous matter, really only makes up a small portion of the matter that’s in the universe. Essentially, the universe has played a trick on us, that we’ve been looking at this one thing and the rest has been hidden, and we really don’t know what it is yet. That opened the floodgates for researchers to really start thinking about “Is dark matter made of dead stars and planets and some of these other objects that we know about, that we can’t see, or is there something else?” In the 1980s, you get to this point where there’s two camps and they’re starting to collect all this different data to try to understand what is it that’s tugging on these stars? What is this dark matter? Because now we have to accept that it exists. HAMMOND: She’s making this contribution in the 1980s. She’s in her 60s or getting into that area. That’s another unusual thing. Scientists usually make the great contributions a little earlier than that. She just kept being productive. YEAGER: Yes, absolutely. Absolutely.
Even the galaxy UGC 2885—this is [also known as] Rubin’s Galaxy. It’s actually named after her. Even into the early 2000s, Vera was still looking at this galaxy, still looking for the farthest stars that she could find, because she wanted to check that her data were correct, and she wanted to know how far out do you have to go before stars’ speeds around the galaxy might drop off? Is there a point where you get that curve that’s flat, and then it starts to level off, and then it starts to get back down? Right? Because then if that’s true in how the galaxy is put together, you might get to the point where you’re running low on dark matter. There’s not that matter to tug on the stars.
Or the other thing that she proposed that I thought was really fascinating is maybe the dark matter halos continue and they actually touch other galaxies. Our dark matter halo could be touching Andromeda’s dark matter halo. There’s been evidence. NASA suggests that that’s not the case. But the fact that she was still curious well into her 70s, to ask those questions and try to find those answers, I thought really just spoke to how curious she was about the universe and about the world around her and really trying to understand what’s going on, and just not ever losing that kind of childhood curiosity.
