Vera Rubin — Astronomer
Often called one of the most gifted but underrated astronomers today, her work confirmed the presence of dark matter in the universe, and since 1978, she has researched and analyzed over 200 galaxies
Born in 1928 in Philadelphia, Vera Rubin was 10 years old and living in Washington, DC when she first fell in love with the night sky, peering up at the heavens from her bedroom window. It was rare for a woman to study science at the time, but she was determined to make her mark. Vera earned a B.S. in astronomy from the prestigious women’s institution of Vassar College in 1948 — the only astronomy degree awarded there that year. She tried to get into grad school at Princeton University, but no women were allowed in the astronomy program (that didn’t change until 1975). Two years later, she wound up earning a master’s degree from Cornell, where she studied physics under such luminaries as Philip Morrison, Richard Feynman, and Hans Bethe. She was later accepted into the Ph.D. program at Georgetown University.
That’s where she met her husband, Robert Rubin, who supported her desire to earn a Ph.D. So much so, that when she attended night classes at Georgetown, he drove her to classes and ate his dinner in the car until class was finished and he could drive her home. (Her parents babysat their young children.)
The hard work paid off: she got her Ph.D. in 1954, with a thesis on the unusual “clumping” of galaxies in the universe — results that were largely dismissed at the time, but were confirmed some 15 years later.
Why She’s Important: After joining the Carnegie Institution in Washington as a research astronomer, she began her focus on observing the dynamics of galaxies, including their velocities and clumping — endeavors which would lead her to confirm the existence of “dark matter” in the universe, a theory which had been proposed by researcher Fritz Zwicky years earlier. Vera teamed up with Kent Ford, an astronomer who had developed an extremely sensitive spectrometer. She and Ford used the spectrometer to spread out the spectrum of light coming from the stars in different parts of spiral galaxies.
In these pursuits, Vera expected to see that the stars were orbiting the center of the galaxy more slowly the further they were from the center, much like the larger outer planets in our solar system take longer to complete an orbit around the Sun than the planets closer in. That’s because the visible mass of a given galaxy — and hence, its gravitational pull — is concentrated at the center.
Instead, Rubin and Ford found that the outer stars were orbiting just as quickly as those at the center. The visible matter wasn’t sufficient to account for this; the spiral galaxy should be flying apart! Clearly, there had to be some kind of hidden “dark” mass adding to the galaxy’s gravitational influence.
And that’s when Rubin remembered encountering as a grad student a 1933 paper by Fritz Zwicky analyzing the velocities of galaxies in the Coma cluster. Zwicky’s paper concluded that the individual galaxies were moving so quickly that they should be able to escape from the cluster if visible mass was the only thing contributing to the cluster’s gravitational pull. Since the cluster hadn’t flown apart, he proposed the existence of “dark matter” (from the German Dunkle Materie) — about ten times more abundant than the visible matter — to account for the observational data.
Rubin and Ford had made a direct observation of Zwicky’s predicted dark matter. Vera soon realized that they had discovered compelling evidence for Zwicky’s dark matter. Many astronomers were initially reluctant to accept this conclusion. But the observations were so unambiguous and the interpretation so straightforward that they soon realized Vera had to be right. The luminous stars, she found, are only the visible tracers of a much larger mass that makes up a galaxy. The stars occupy only the inner regions of an enormous spherical “halo” of unseen dark matter that comprises most of a galaxy’s mass.
Other Achievements: After her momentous discovery, Vera Rubin continued to explore the galaxies. For instance, in 1992, she discovered a galaxy (NGC 4550) in which half the stars in the disk are orbiting in one direction and half in the opposite direction, with both systems intermingled! More recently, she and her colleagues found that half the galaxies in the great Virgo cluster show signs of disturbances due to close gravitational encounters with other galaxies. In recognition of her achievements, Vera Rubin was elected to the National Academy of Sciences and in 1993 was awarded the National Medal of Science.
In Her Own Words: Throughout her career, Vera, who is currently 84 years of age, has not sought status or acclaim, even though a growing number of scientists believe she is long overdue for receiving the Nobel Prize for her work. Rather, her goal has been the personal satisfaction of scientific discovery. After her dark matter discovery, she wrote: “We have peered into a new world and have seen that it is more mysterious and more complex than we had imagined. Still more mysteries of the universe remain hidden. Their discovery awaits the adventurous scientists of the future. I like it this way.”
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