Rubin, who was 88, had been a favorite among her peers not only for her role in redefining the ingredients of the universe as we know it—a discovery that made her a perennial favorite for the vaunted Nobel Prize in physics—but also for her unrelenting graciousness and her desire to improve the position of women and minorities in astronomy.
She was, by all accounts, a gifted scientist as well as a nurturing mentor and an inspiration to those still working their way up the academic ladder. After all, this was a woman who trail-blazed her way through an academic system that perpetually slammed doors in her face and ignored her results.
“Science progresses best when observations force us to alter our preconceptions,” Rubin has said.
Perhaps that statement is as much about the sociology of science as it is about the results.
Born July 23, 1928, Rubin became fascinated with astronomy when she was a kid growing up in Washington, D.C. There, she would watch the stars from her bedroom window, marveling at the precise paths they followed across the sky, tethered to an invisible point at Earth’s celestial pole.
It’s an epic bit of foreshadowing, because nearly five decades later, Rubin’s most spectacular contribution to astronomy would also be based on the motions of stars: in this case, the whirling dance of far-away pinpricks of light orbiting the cores of glittering spiral galaxies.
But first, Rubin needed to barnstorm the world of astronomy.
After earning a bachelor’s degree in astronomy from Vassar College in 1948, Rubin attempted to pursue graduate work at Princeton University and was met with a resolute “no”—the school’s graduate program didn’t admit women until 1975. (Read about the female astronomers who broke the glass ceiling at the Harvard Observatory in the 19th century.)
Undeterred from her passion for the cosmos, Rubin instead went to Cornell University, where she worked with luminaries such as Philip Morrison, Hans Bethe, and Richard Feynman. She left with a master’s degree and returned to Washington, D.C. to complete her Ph.D. at Georgetown University.
There, her 1954 doctoral thesis revealed that galaxies tended to clump together in space rather than being haphazardly sprinkled throughout the universe. Today astronomers acknowledge that the large-scale structure of the universe involves clumps of galaxies strung together like beads on a web. But Rubin’s observations of this structure were mostly ignored for the better part of two decades.
In the late 1960s, Rubin and collaborator Kent Ford took a close look at the Andromeda Galaxy, the closest spiral galaxy to our own Milky Way. Then on staff at the Carnegie Institution for Science in Washington, D.C., Rubin was studying the rotation rates of stars whirling around the cosmic spiral, expecting to find that—as Isaac Newton had predicted—the stars nearest the galactic core would be moving more quickly than those on the fringe.
But that’s not what Rubin saw. In fact, the stars at Andromeda’s edge were zooming around so fast that all calculations suggested they should be flying off into space. The astronomers couldn’t see anything in the edges of the galaxy that contained enough mass, and therefore gravity, to keep those stars tethered.
And yet Andromeda was somehow holding itself together.
Intrigued, Rubin and Ford measured the rotation rates of stars in another 60 galaxies. Over the next several years, the results were all the same, suggesting that something fundamental was missing from our understanding of how the universe is put together.
That’s the point at which Rubin remembered the 1933 observations of Fritz Zwicky. The Caltech astronomer had been studying the motions of galaxies swirling around the Coma cluster, a giant swarm of galaxies bound together by gravity.
His observations revealed that the cluster’s galaxies were moving so quickly they should be escaping into the cosmos—like the stars Rubin had seen. Zwicky had concluded that some type of massive, unobservable substance was lending gravitational heft to the cluster and helping to keep the thing intact.
Rubin realized that her observations also pointed to the existence of this cosmic glue. Without it, there would be no galaxies, and no galaxy clusters.
Today, this invisible substance is called dark matter, and it is an accepted, if enduringly mysterious, ingredient of the cosmos. Dark matter is currently thought to make up some 90 percent of the mass of the universe—we just can’t see it.
That’s because dark matter doesn’t interact with normal matter except via gravity. Over decades, numerous experiments have tried to find and identify the dark matter particle, but it’s proving to be a slippery, elusive beast.
Still, thanks to Rubin and her colleagues, we know that dark matter must exist—either that, or we need to revise our basic understanding of the way gravity works.
“In a spiral galaxy, the ratio of dark-to-light matter is about a factor of ten,” Rubin has said. “That's probably a good number for the ratio of our ignorance-to-knowledge. We're out of kindergarten, but only in about third grade."
On Equal Ground
In addition to her scientific advances, Rubin fought hard for the equality of women in astronomy. She would call conference organizers and point out their lack of diverse speakers. She fought for women to be accepted at Washington’s exclusive Cosmos Club.
And when she became the first woman to observe at the Palomar Observatory outside San Diego in 1965, she taped a paper skirt to one of the exclusively male bathroom signs.
“She said, ‘There you go; now you have a ladies’ room,’” recalled Princeton physicist Neta Bahcall in an interview with Astronomy magazine.
Over her career, Rubin collected a number of illustrious prizes for her work. She was elected to the National Academy of Sciences in 1981. She was the first woman to receive the Royal Astronomical Society’s gold medal since Caroline Herschel in 1828. She was awarded the National Medal of Science in 1993. And she occasionally met with then First Lady Hillary Clinton to talk about science.
Most astronomers agree that Rubin’s evidence for dark matter is a fundamental cosmic discovery. That’s why her colleagues continually expected her to also be awarded the Nobel Prize, which for many scientists still represents the pinnacle of academic achievement.
But Rubin was continually passed over, and with the Nobel rules prohibiting posthumous awards, her chances are now as invisible as the stuff she discovered—despite the fact that few of her peers would argue about the quality of her work.
“From now on I'm not going to engage in arguments about Nobel Prizes,” tweeted planetary scientist Sarah Hörst. “I'll just say ‘Vera Rubin’ and walk away.”