Vera Rubin sent ripples throughout the scientific community, as her work proposed a novel recipe for our universe. While we once believed our universe to be full of matter, Rubin led us to see a universe dominated by dark matter and dark energy. Today, we understand the universe to be made up of nearly 95% dark energy and dark matter, leaving only 5% of baryonic matter (protons, neutrons, tables, chairs, humans, dogs, etc.). Despite its dominating presence, dark matter properties remain mysterious! For example, dark matter does not emit light or energy. Though difficult to detect, Vera Rubin guided the field of cosmology to determine this mysterious source of matter must dominate in our universe. This is the story of Dr. Rubin’s journey from astronomer to queen of the cosmos.
A Star in Motion
Vera Cooper Rubin was born July 23rd of 1928 in Philadelphia, Pennsylvania to two Jewish immigrant parents. Rubin wasted no time in exploring the cosmos. Her father, an electrical engineer, gifted her a telescope which she would use to explore the sky, far past her bedtime. But she wasn’t just looking at constellations; she sought to understand the motions of the stars. By high school, Rubin had made up her mind: she would be an astronomer. “I didn’t know a single astronomer, but I just knew that was what I wanted to do,” she said in an interview with the American Institute of Physics.
One of Rubin’s role models, astronomer Maria Mitchell, was the first astronomy professor at Vasaar College, an all-women’s college in New York. This, and a scholarship, led Rubin to attend Vasaar College where she would study astronomy and earn her bachelor’s degree in 1948. She hoped to continue her studies at Princeton University, though the Astronomy Department did not accept women. Unfazed, Vera continued her education in astronomy at Cornell where she received her Master’s of Science in 1951. Rubin earned her PhD from Georgetown University in 1954, with a focus on the “fluctuations in the space distribution of galaxies.”
Rubin joined the Carnegie Institution’s Department of Terrestrial Magnetism in 1965. She teamed up with astronomer W. Kent Ford Jr. and set out to map the mass distribution in spiral galaxies. To do this, they would create “rotation curves”, measuring how fast stars were rotating in a galaxy versus their radial distance from the galaxy’s center. The Newtonian law (first published by Isaac Newton in 1687) relates the force acting on a mass to the mass’s distance from the center of its orbit:
For example, the force acting on any star rotating around a galaxy’s center is expected to decrease as we travel from the galaxy’s center. Rubin and W. Kent Ford Jr.’s measurements told a very different story.
In 1978, they published the rotation curves of 10 galaxies (Fig. 2). To their surprise, the stars on the outskirts of the galaxies were not slowing down… in fact they sped up! This suggested there was some extra mass responsible for speeding up the stars. This extra mass is what we now understand to be dark matter. Rubin continued measuring the rotation curves of galaxies, reinforcing the theory that galaxies are surrounded by dark matter, pushing stars on the outskirts to zoom around their center.
Though overlooked by the Nobel Prize Committee (often cited as a major oversight), Dr. Vera Rubin was elected to the National Academy of Science in 1981 and was awarded the National Medal of Science by President Bill Clinton in 1993 (to name a few of her many accolades). When Vassar College awarded her the Distinguished Achievement Award in 2007, she said her education had given her “the confidence that I could learn anything I wanted to know.” Rubin continued to study the cosmos and lead an active research life until final years of her life, publishing the rotation curves of dozens more universes.
Rubin passed away December 25th of 2016 in Princeton, New Jersey at 88 years old. Her love for astronomy continues to inspire those who follow. The upcoming Large Synoptic Survey Telescope in Chile, a decade-long survey with the mission to study dark matter, will be named The Vera C. Rubin Observatory. This is the first national observatory named after a woman.
Her work pushed astronomers to probe the composition of galaxies, modelling mass distribution throughout the universe. Rubin’s spirit shines throughout her career, as she unearthed fundamental truths of the universe while inspiring those who follow. We stand on the shoulders of giants and are lifted to the cosmos by Vera.
Grace E. Chesmore is an experimental cosmologist and graduate student at the University of Chicago in the Department of Physics. She received her B.A. in physics at Santa Clara University in 2017 and her M.S. in physics at the University of Michigan in 2019. She researches the cosmic microwave background, optimizing optical properties for the Simons Observatory. You can follow her on twitter @gracechesmore1 .