Vera Rubin

"In a spiral galaxy, the ratio of dark-to-light matter is about a factor of ten. 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." — Vera Rubin

Vera (Cooper) Rubin (born July 23, 1928 (age 85)) is an American astronomer who pioneered work on galaxy rotation rates. She is famous for uncovering the discrepancy between the predicted angular motion of galaxies and the observed motion, by studying galactic rotation curves. This phenomenon became known as the galaxy rotation problem.

In the 1970s, Rubin found evidence of a hypothetical type of invisible matter now called dark matter. Her calculations showed that galaxies must contain about ten times as much “dark” mass as can be accounted for by the visible stars. In short, at least ninety percent of the mass in galaxies, and therefore in the observable universe, is invisible and unidentified. Then Rubin remembered something she learned as a graduate student about earlier evidence for unseen mass in the universe. In 1933, Fritz Zwicky had analyzed the Doppler velocities of whole galaxies within the Coma cluster. He found that the individual galaxies within the cluster are moving so fast that they would escape if the cluster were held together only by the gravity of its visible mass. Since the cluster shows no signs of flying apart, it must contain a preponderance of “dark matter”—about ten times more than the visible matter—to bind it together. Zwicky’s conclusion was correct, but his colleagues had been skeptical. Rubin realized that she had discovered compelling evidence for Zwicky’s dark matter. Most of the mass of the universe is indeed hidden from our view.

Many astronomers were initially reluctant to accept this conclusion. But the observations were so unambiguous and the interpretation so straightforward that they soon realized Rubin had to be right. The luminous stars 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. Perhaps there are even major accumulations of dark matter in the vast spaces between galaxies, without any visible stars to trace their presence. But if so, they would be very difficult to observe.

Vera Rubin continues to explore the galaxies. 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! Perhaps this resulted from the merging of two galaxies rotating in opposite directions. Rubin has since found several other cases of similarly bizarre behavior. 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. But throughout her career, Rubin has not sought status or acclaim. Rather, her goal has been the personal satisfaction of scientific discovery. “We have peered into a new world,” she wrote, “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.”

Posted 6 months ago with 328 notes
Tagged:women in stemsciencevera rubinastronomerscientistastronomy

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