On Dec. 25, 2016, astronomer and Vassar alumna Vera Rubin ’48 sadly passed away at the age of 88, a solemn yet graceful conclusion to a life rich with brilliant research and revolutionary ideas on both the universe and the role of women in the sciences. But upon the announcement of her death, countless news publications have fallen into the trap of over-dramatizing Rubin’s life and achievements by establishing her as the person who “discovered” dark matter.
An article by The Washington Post labeled her as a pioneer who “confirm[ed] the existence of dark matter,” while an article by NPR ran the headline, “Vera Rubin, Who Confirmed Existence of Dark Matter, Dies at 88.” Even Vassar’s own webpage on Vera Rubin stated that “Rubin is credited with proving the existence of ‘dark matter.’”
This is not true. Vera Rubin did not discover dark matter, nor did she confirm its existence. In fact, no one has. Dark matter remains an unproven theory, a hypothesis that researchers are still studying today. Vera Rubin herself has stated several times that she didn’t “prove” anything. What she actually did was uncover a strange oddity while studying galaxy rotation rates and postulate that the conventional understanding of our universe was flawed. In order to truly appreciate Rubin’s legacy without exaggerating her achievements, we need to understand the importance of what she noticed and why this anomaly remains a highly controversial topic among modern astronomers.
In the early 1970s, the entire world was embroiled in the matters of astronomy as the Space Race between the United States and the USSR reached its peak following Neil Armstrong’s first steps on the moon in 1969. At the time, Rubin was studying galaxy rotation curves with her colleague W. Kent Ford Jr. at the Carnegie Institute of Science. Her goal was to map the distribution of mass in spiral galaxies by measuring how fast the stars in those galaxies were rotating around the center.
According to Newton’s law of universal gravitation, the star closer to the center of the galaxy should orbit faster than the star that is farther away. This is because the closer the star is to the center, the more it feels the gravitational pull of the galaxy’s center, and the faster it moves. Prof. Colette Salyk, an assistant professor of Astronomy at Vassar, compares the rotation of the stars to swinging a ball tied to a string: “The harder you pull on the string, the faster the ball will travel…Gravity has everything to do with the speed of stars, since gravity provides the force that keeps the star in orbit.”
In other words, Vera Rubin was tracking how fast the stars were moving in order to determine the force of gravity they felt and thus how much mass they have. By this logic, the stars at the edge of the galaxy should be moving slower than those near the center. However, Rubin discovered a contradiction: The stars at the edge of the galaxy were not orbiting slower than those near the center.
In fact, they were moving so fast that the galaxy should have been flying apart. Given this discrepancy, Rubin proposed that some sort of unseen mass was holding their orbits together. This invisible mass that doesn’t radiate light is what people commonly refer to as dark matter.
To reiterate, Vera Rubin did not discover dark matter in this instance. The concept of invisible matter holding together galaxies has been around since Swiss astronomer Fritz Zwicky first suggested it in 1933. What Rubin’s discovery really did was provide detailed calculations regarding dark matter that swayed many astronomers to believe in its existence. By the time Rubin finished her investigation, she determined that each spiral galaxy possesses a “halo” of dark matter and that more than 90 percent of the universe is composed of this material. At that point, many astronomers were already convinced.
But as stated earlier, the dark matter hypothesis is still a hypothesis. Once the scientific community agreed on the concept of dark matter, they did everything they could to find decisive evidence for it. Unfortunately, even after three decades of intensive searching and developing expensive technology specifically designed to detect dark matter, astronomers have yet to find any signs of ever getting close. The latest blow to the dark matter hypothesis came in January 2017 when the promising XENON100 dark matter detector failed to offer any positive results.
Astronomer Stacy McGaugh at Case Western Reserve University aptly surmised the grim situation: “This generation of detectors should be the last. If we don’t find anything, we should accept we are stuck and need to find a different explanation, perhaps by modifying our theories of gravity, to explain the phenomena we attribute to dark matter.”
In truth, Vera Rubin herself began having doubts as early as 2006. In a 2011 interview, Rubin wondered whether the galaxy rotation problem that brought dark matter into fame was actually a flaw in our understanding of gravity. When asked if she really believed that dark matter wasn’t the solution, Rubin shrugged and asked “Why not?” And this response illuminates what science is really about: The willingness to broaden our understanding of the universe, even at the expense of one’s pride. The value of science stems from this pursuit of knowledge, not the fame and prestige that come with a scientific discovery.
However, it is not as if the theory of dark matter has been disproven. There are still countless astronomers who are hard at work in search of dark matter. But, one significant contribution that is not up for debate is Rubin’s role as a pioneering advocate of women in the sciences. All throughout her life, she faced brutal and humiliating opposition towards her position as a scientist.
Teachers and colleagues alike pushed the notion that science was a men-only field and Rubin was often chastised for intruding where she didn’t belong. Yet, she continued to break boundaries, becoming the only astronomy major to graduate from Vassar in 1948 and eventually receiving the National Medal of Science in 1993. As Rubin once stated, “There is no problem in science that can be solved by a man that cannot be solved by a woman.” That alone should be enough for us to honor her legacy as a truly brilliant scientist.
Originally published on February 1, 2017, in The Miscellany News: Public misconceptions of Vera Rubin’s career pervade news cycle