Photo by Linda Davidson/The Washington Post via Getty Images
Vera Rubin didn’t “discover” dark matter, but she put it on the map.
Dark matter is a wild concept. It’s the idea that
some mind-boggling percentage of all the matter in the universe may be
invisible, and wholly unlike the matter that makes up Earth. Rubin is
celebrated because she forced much of the astronomy community to take it
seriously.
That reckoning moment came in 1985, when she stood
in front of the International Astronomical Union and walked the audience
through some of the data she had collected.
Her data showed that stars at the edges of multiple
galaxies were moving in ways that didn’t make sense, according to the
rules of physics. One possible explanation for this strange phenomenon,
Rubin suggested, was the existence of a mysterious “dark matter” at the
edges of the galaxy. In the decades since that talk, research into dark
matter has exploded, revolutionizing astronomy.
In Bright Galaxies, Dark Matter, and Beyond,
a 2021 biography of Rubin, science journalist Ashley Yeager explains
how Rubin, who died in 2016, grew from a young researcher whose bold
ideas were initially ignored into the kind of scientist who could change
an entire field. In 2020, we interviewed Yeager for an episode of the Unexplainable podcast about dark matter. A transcript of our conversation, lightly edited for length and clarity, follows.
Noam Hassenfeld
When did Vera Rubin first get interested in astronomy? What’s her origin story?
Ashley Yeager
About the age of 11 is when she started to look at
the stars. Vera and her sister, Ruth, shared a bedroom in their
Washington, DC, townhouse. And Ruth remembers Vera constantly crawling
over her at night to be able to open the windows and look out at the
night sky and start to track the stars. So clearly, Vera was captivated
by the night sky. And that stuck with her.
She then went to Vassar, where she studied
astronomy. [While at Vassar, she met a mathematician named Robert
Rubin.] They ended up getting married. And that drove one of
the biggest decisions in Vera’s life, because she wanted to go to
graduate school for astronomy.
She’d gotten into Harvard,
but Robert Rubin was at Cornell. He was well into his graduate studies.
They had to make a choice, and Vera said, “Let’s stay together. I’ll
come to Cornell with you and I’ll do my master’s in astronomy while you
finish your PhD in physics.”
Noam Hassenfeld
Isn’t that kind of a wild choice? To choose Cornell based on a husband?
Ashley Yeager
It’s the late 1940s. And Vera, in some ways, was
very traditional, even though she was nontraditional in other ways. She
felt that she was expected to get married by the end of her four years
at Vassar. That was still something that was societally kind of
expected.
And I actually think it set her up to be more
successful than maybe she would have been, had she gone to Harvard or
Princeton or somewhere else, just because of the exposure that she got.
There was intellectual freedom she had at Cornell, to be able to probe
into different questions in astronomy that she probably would have been
pushed away from, had she been in a more structured graduate program.
Noam Hassenfeld
So she’s at Cornell. She’s probing into questions.
She’s got a lot of intellectual freedom. What are the big questions that
are occupying her mind?
Ashley Yeager
The biggest one, which becomes her master’s thesis, is really the idea of “Does the universe rotate?”
Noam Hassenfeld
Wait, does the universe rotate?
Ashley Yeager
So, probably no.
This was a question posed by a very eccentric astronomer named George
Gamow. Vera’s husband actually showed Vera this paper that George Gamow
had written about this idea. And she thought, “Well, why would we not
try to answer that question?”
Noam Hassenfeld
The kind of question that, if she were at another
university, maybe she wouldn’t have had the freedom to dive into?
Ashley Yeager
I think so. I get the sense, reading through the
literature and looking through the history, that she probably would have
been guided to a more traditional question.
And as she started to look through the data, the
numbers started to suggest that there was this odd, sideways motion that
perhaps could be interpreted as a universal rotation. She presented her
idea to her master’s thesis adviser, William Shaw.
He says, “Your conclusion is really good. I want to
present it under my name at this upcoming astronomy conference.”
And Vera is like, “No! I might not be a member of
this society yet. But you’re not presenting my data for me. I’m going to
present it under my own name, come hell or high water.”
Noam Hassenfeld
So does she?
Ashley Yeager
Yes. She goes to this meeting. Apparently, the drive
from New York to Pennsylvania, where the meeting was, was harrowing. It
was the winter, snowy. They had a newborn in the car. Her dad was
actually driving because he was the only one with a car at the time.
But she gives the presentation, and the reaction is
less than great. There are some heavy critics in the room. A lot of
scoffing. She does have one person, Martin Schwarzschild, who encourages her. He says, “This is really interesting. But we need more data to be able to make this conclusion.”
And that’s a criticism that really sticks with her
throughout her career. Later on, she really tries to have or collect as
much data as possible to support her conclusions, just because of that
experience.
Noam Hassenfeld
What happens next?
Ashley Yeager
She takes a little bit of a break, because she
really has this strong sense of wanting to set up a home and start a
family. There’s this moment in the early 1950s, when she’s at the
playground with her son. She had been reading astrophysical journals to
stay connected with what was going on in astronomy.
So her son’s playing in the sandbox and she’s
reading the journal, and she just breaks into tears because she misses
doing research so much. She misses that curiosity of asking questions
and searching for data, and really trying to figure out the answers to
how the universe works.
It’s at that point that her husband says, “You need
to go back to school. It’s time. We’ll figure out child care. We’ll
figure out how to get dinners made. But let’s do it.”
Noam Hassenfeld
So she goes back into astronomy. And eventually she starts doing research at Kitt Peak National Observatory, right? What’s that like?
Ashley Yeager
We’re talking late 1960s. This is a 84-inch
telescope, very large. Vera is at the telescope with Kent Ford, her
collaborator. They’re looking at this galaxy called Andromeda, which is
our nearest neighbor. They’re looking at these really young, hot stars
on the edge of the galaxy, and they’re trying to get the speeds of these
stars — how fast are these stars going around Andromeda?
So they’re looking at the data, and they’re going,
“Oh my gosh, this is not what we expected.” The assumption was that the
stars closer in would fly around the sun fast, and the stars farther out
would go super slow. But these stars were moving faster than they
expected.
The only way for those stars far out in the galaxy
to move that fast is [that] there’s got to be something happening out
there that we don’t understand.
Noam Hassenfeld
What does she think is going on?
Ashley Yeager
Well, she’s not really sure. And again, she doesn’t
like to make assumptions or speak without data. So she and Kent Ford,
and a couple other people, they really start to do a systematic study of
galaxies.
She does 20 galaxies, and then 40, and then 60. And
they all show this bizarre behavior of stars, these stars out far in the
galaxy, moving way, way too fast. So at that point, you know, the
astronomy community is like, “Okay, we have to deal with this.”
In 1985, Vera Rubin gives this talk at the IAU.
She says, “Nature has played a trick on us. That we have been studying
matter that makes up only a small fraction of the universe. The rest of
the universe is stuff that we don’t understand, and we can’t see it.”
And I think because she did this in so many galaxies
— we’re talking 60 galaxies — there was really no denying it. It was
really her work that pushed the community over the edge, to say we have
to accept the idea that dark matter exists.
Noam Hassenfeld
It sounds like if you really want to upend our
entire conception of the universe, you have to come with some data.
Ashley Yeager
Yeah, absolutely. Because she held onto that
criticism of her master’s and PhD work — she would just go after the
data, and really make sure that the story she told from that data rang
true.
One of the things that made her a remarkable
scientist is her perseverance. She did face a lot of roadblocks,
especially because she was a woman in science in the 1940s, 1950s,
1960s. She had to really persevere. Unfortunately, she will never get to
see or know what dark matter is. But I don’t know that she had a
problem with that. She would take pride in the fact that she opened a
whole new realm of astronomy and physics.
She basically created more questions than answers,
and I think that’s the mark of a remarkable scientist: when you open up
these questions that no one ever thought of before. When you create a
whole new generation of scientists who can go and answer them.
