Vera Cooper Rubin

Although her ideas on the nature of the universe were at first largely discounted, astronomer Vera Cooper Rubin (born 1928) has gained recognition for her research leading to the discovery of "dark matter."

Vera Cooper Rubin's measurement of the speed of spinning galaxies suggests that science has only scratched the surface of the true nature of the heavens. Dark matter is believed to make up 90 percent of the universe. It is material that is thought to exert gravitational force on stars to keep them spinning inside their galaxies.

Watched the Stars

Rubin was born on July 23, 1928, in Philadelphia, Pennsylvania. At age 10, she was already fascinated by the stars. From her home in Washington, D.C., she searched the skies and watched the constellations until late at night. Despite warnings from her mother not to overdo her star gazing, Rubin continued to pursue her passion in the night skies. At age 14 she built her first telescope with the help of her father. Her early fascination for astronomy followed her into adulthood; now she scans the stars with some of the world's largest and most powerful telescopes.

Even though a high school physics teacher warned Rubin away from science, and an admissions officer at Swarthmore College in Pennsylvania advised her to major in something more suitable than astronomy, Rubin went her own way. She was determined to investigate the universe's secrets for herself. She earned her bachelor's degree in astronomy at Vassar College in 1948 and went on to earn a master's degree from Cornell University in 1951. At Cornell she studied quantum mechanics with Hans Bethe, who later won a Nobel Prize for his research on fusion reactions in the sun, and attended lectures on quantum electrodynamics given by Richard Feynman, who later won a Nobel Prize for his research on particle interactions. Rubin's thesis challenged the big bang theory which postulates that the universe is expanding out from an original central explosion of matter. Instead, she argued, the galaxies themselves are actually rotating around a central point, not just expanding out from it. "My first paper got an enormous amount of publicity, almost all negative," Rubin told Discover. "But, at least, from then on, astronomers knew who I was."

Rubin, then a young woman of only 22 years, had no intention of stirring up controversy with her work. But her findings were unorthodox and continued to be so. In 1954, while working toward a doctorate from Georgetown University at night, Rubin completed research that showed galaxies were not evenly spaced throughout the universe. This was another controversial finding, since the big bang theory suggested that galaxies are evenly distributed. For years Rubin carefully measured the speed of spiral galaxies. She found that they spin so fast that their stars ought to spin away from them, rather than stay in orbit. Perhaps, she thought, galaxies remain intact due to gravitational forces exerted by matter that human technology cannot detect: so- called "dark matter."

Astronomers knew that the universe was expanding because of the shift toward red exhibited by light waves emanating from distance galaxies. This red shift indicates movement away from Earth at speeds so high that astronomers found it hard to believe that stars within these galaxies were not actually spinning out of them. (Blue light, on the other hand, would indicate a movement toward Earth.) An accepted explanation for star movement within galaxies was that, much like planets in orbit around the sun, stars on the edge of a galaxy moved more slowly than those closer in. Prior to Rubin's discovery that stars on the edge of a galaxy moved just as quickly as others, many astronomers believed that the laws of physics dictated that stars would behave more like planets. Rubin's research changed all that.

Discovered "Dark Matter"

The gravitational pull of large bodies such as the Sun lessens as distance increases; therefore, if stars on the edge of a galaxy were moving just as swiftly as the rest of the stars in their galaxy, what was keeping them from spinning away? The answer seemed to be another gravitational force, a cosmic force that was at work although not visible through a telescope.

In the 1970s, while other astronomers pursued quasars (blue specks of light thought to be the birthing place of galaxies), Rubin and her colleague W. Kent Ford investigated galactic movement. They looked into the possibility that galaxies did not just expand in a predictable manner toward a region called the Great Attractor, but rather moved on their own. The idea was not received well, so Rubin turned her attention to the rotation of spiral galaxies. After she discovered that the Andromeda Galaxy was actually moving at a fast rate but that stars were not spiraling away from it, she went on to investigate other galaxies. She found that, far from being the exception to the rule, Andromeda was behaving much the same as other galaxies. Stars on the edge of the galaxy moved with the same speed as those on the interior. Some kind of matter must be exerting a force on those stars to keep them from out of the galaxy.

Rubin began to hypothesize that the mass of the galaxy was spread out rather than concentrated in one central spot. If the velocities of clouds farther out from the "central bulge" of a galaxy were not less than the velocities of clouds closer in, as Keplerian motion predicts, then all mass in the galaxy must not be at its center. Could it be that there were heavenly bodies generating mass as yet unknown to astronomers?

Although Rubin's work was not easily accepted in the 1970s, she was not the first astronomer to notice galaxies were moving too fast to stay together. In the 1930s astronomers Fritz Zwicky and Sinclair Smith had realized that galaxies were speeding along at higher rates than expected, and they wondered if some kind of matter was keeping galaxies together through gravitational pull. Their idea about "missing mass" influencing galactic movement seemed to agree with Rubin's findings.

It took some time, but after studying more than 200 galaxies, Rubin and her colleagues documented enough data to convince other astronomers that the universe was virtually 90 percent undiscovered matter. Thanks to Rubin's efforts, the possible existence of dark matter became scientifically accepted.

"So important is this dark matter to our understanding of the size, shape, and ultimate fate of the universe that the search for it will very likely dominate astronomy for the next few decades," Rubin wrote in an article published in the Scientific American. The findings from Rubin's research opened new vistas for exploration. "With over ninety percent of the matter in the universe still to play with, even the sky will not be the limit," she explained to Discover.

The possible existence of dark matter set the scientific world agog with curiosity. Some astronomers, such as Rubin, believe the dark matter was ordinary in make-up--just defunct stars or planets--but others believe it was an entirely different substance, made of particles that weighed 100 times more than visible matter. While the truth of the matter as yet remains a mystery, Rubin's research gained considerable respect within the scientific community. For all the attention her work received, Rubin remained more interested in the work itself. "Fame is fleeting," she told Discover. "My numbers mean more to me than my name. If astronomers are still using my data years from now, that's my greatest compliment."

Shared Passion for Astronomy with Others

Years before she asked for a job at the Department of Terrestrial Magnetism (DTM) at the Carnegie Institution of Washington in 1965, Rubin already had an interest in DTM. After she became a staff member there, she enjoyed the freedom to pursue her interests without the pressure to publish. The family-like atmosphere at DTM included daily staff lunches and scientific discussions. It was the right place for Rubin to thrive. David Burstein, who worked with Rubin from 1977 to 1979, noted that she always found personal satisfaction in her work that had nothing to do with money or publicity.

As Rubin changed modern understanding of the universe, she shared her vision with the younger generation through teaching. From 1954 to 1955 she served as an instructor of mathematics and physics at Montgomery County Junior College. From 1955 to 1965 she was a research associate astronomer at Georgetown University and from 1959 to 1965 was a lecturer then assistant professor of astronomy at Georgetown University. Even after she accepted a research position, Rubin taught astronomy courses at her children's high school and served on an advisory board for an inner-city youth science program. She also worked with the National Academy's Committee on Human Rights.

Despite her years of teaching, it was not until 1963 that Rubin began to feel like an astronomer. She worked at the University of California at San Diego with Margaret and Geoffrey Burbidge, who had done notable research indicating that chemical elements are made in stars. Rubin felt she was finally working with people who were interested in what she had to say and that her ideas had credibility. Rubin became a professional observer at Kitt Peak in Arizona before she settled on her career at DTM and was the first woman allowed to observe at Palomar Observatory.

Personal

Rubin is married to Robert Rubin, whom she met while he was a fellow graduate student at Cornell University majoring in physical chemistry. Robert chauffeured Rubin, who does not drive, back and forth to class while she was working on her Ph.D. At the time, Rubin's parents helped her take care of her first two children. All four of her children have since earned doctorates in scientific fields. David (born 1950) has a Ph.D. in geology, Judy (born 1952) has a Ph.D. in cosmic-ray physics, Karl (born 1956) has a Ph.D. in mathematics, and Allan (born 1960) has a Ph.D. in geology.

Because of her struggles to gain credibility as a woman astronomer, Rubin continued to encourage young girls to pursue their dreams of investigating the universe. She wrote a children's book titled My Grandmother Is an Astronomer in the hopes that other children will experience some of the joy she feels watching the night skies.

Further Reading

• Discover, October 1990.
• Scientific American, March 1998.
• Biography.com, http://search.biography.com/ (October 15, 2001).
• "Vera Rubin and Dark Matter," CWP at Physics, UCLA, http://www.physics.ucla.edu/~cwp/ (October 15, 2001).
• "Vera Rubin's Dark Universe," Lake Afton Public Observatory Web site, http://web.physics.twsu.edu/lapo/ (October 15, 2001).