From Lake Afton Public Observatory:

Vera Rubin's Dark Universe

by Katrina Thompson


In Washington, D.C. in 1938, ten-year-old Vera Cooper began watching the night sky from her north-facing bedroom window. She has been stargazing ever since, but she could not have foreseen the impact her studies have made on our perceptions of the universe. She earned her B.S. in astronomy from Vassar in 1948 and her M.S. from Cornell in 1950. (She naively wrote to Princeton for their graduate catalog, but never received it: Women were not allowed in its graduate astronomy program until 1975.) At Cornell she met and married Robert Rubin. She took quantum mechanics from Hans Bethe and quantum physics from Richard Feynman. During graduate school, she began to develop a knack for questioning assumptions.

She produced a controversial master's thesis, presented her findings in 1950 at a meeting of the American Astronomical Society, and promptly received a huge amount of publicity--all negative.

Her ambition led her to Georgetown, the nearest university with a Ph.D. astronomy program. For two years, her husband drove her to classes at night and ate supper in their car while her parents watched the children. Her 1954 doctoral thesis asked whether galaxies were distributed in clumps or at random. She concluded that there was a noticeable clumpiness in the spread of galaxies. These results were confirmed 15 years later, but at the time, no one seemed interested.

She taught and did a little research at Georgetown in the 1950's, but is especially proud of what else she was doing then. She lists the following accomplishments ahead of all her awards and honors: David (1950), Ph.D. geology; Judith (1952), Ph.D. cosmic-ray physics; Karl (1956), Ph.D. mathematics; and Allan (1960), Ph.D. geology.

Rubin spent 1963 working with Margaret and Geoffrey Burbidge. This year was very significant to her, because they listened to her ideas and thus made her feel, at last, like an astronomer. Upon her return to Washington, she got a job at the Carnegie Institute's Department of Terrestrial Magnetism, a place she had visited years earlier and fallen in love with. David Burstein, who worked with Rubin as a postdoc, said, "Vera established an atmosphere where it was a joy to do astronomy...she often told me, 'You don't do astronomy for money or publicity; you do it for your own satisfaction.'"

Rubin began working with Kent Ford and returned to the topic of her master's thesis. They reached the same conclusion Rubin had years earlier, and again the results were questioned. Heated debates about the their work ensued in the astronomical community and some astronomers even pleaded with Rubin for her to stop doing this research. The confrontational atmosphere was more than Rubin wanted, and she and Ford opted to pursue a quieter area of research. She decided to learn why spirals vary in their brightness and their structures, and guessed it had something to do with the galaxies' rotations. The Burbidges had measured rotation rates for galactic centers, but Rubin wanted to know what happens farther out. She and Ford began using a spectrograph to study rotations of galaxies. The spectra of the first galaxy (Andromeda) they examined did not appear as either one of them thought it should. At that time, it was thought that the distribution of mass in a galaxy followed the same pattern as the distribution of light. Thus the brighter area in the center should have more mass, and a greater velocity, than the less luminous outer reaches of the arms. Just like our solar system, the mass closer to the center was supposed to rotate faster than the outer edges of the galaxy. If the mass near the center moved faster and that near the edges moved slower, a graph of the velocities should be a curve showing that the velocities would decrease greatly far from the center of the galaxy.

Instead, what Rubin saw was a straight line as far out as the galaxy seemed to go. That meant that the stars at the edges were travelling around the center just as fast as those near the center. How could this galaxy keep from flying apart? Rubin thought at first that the Andromeda galaxy was just peculiar, so she didn't make a big deal about it. She and Ford continued to measure more spectra of other spiral galaxies and the results were the same. Then Rubin remembered an exercise in graduate school that every student had to work through. It was based on measurements of galaxies in clusters made by Fritz Zwicky in the 1930's. He said that galaxies in clusters moved so fast that they must have some unknown matter (which he called "missing mass") that was gluing them together.

Rubin realized that the dark matter she and her colleagues had observed could be the missing mass Zwicky had predicted. Since 1978, Rubin and a team of Carnegie postdocs have analyzed more than 200 galaxies. They estimate that 90% or more of the universe is made of this mysterious dark matter. In other words, everything astronomers had studied until the discovery of dark matter was only one tenth of the universe.

Today, Rubin continues research on the velocities of galaxies and is sought after to give lectures and interviews. When Rubin was elected to the National Academy of Sciences in 1981, she commented that "Fame is fleeting. My numbers mean more to me than my name. If astronomers are still using my data years from now, that's my greatest compliment." She has opened the door to a great mystery of the universe for future astronomers to unravel. She said, "In a very real sense, astronomy begins anew. The joy and fun of understanding the universe we bequeath to our grandchildren--and to their grandchildren. With over 90% of the matter in the universe still to play with, even the sky will not be the limit." [Quotes are from Discover. October, 1990.]

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