[In honor of Women's History Month, 13.7 Billion Years remembers 22 female scientists throughout history who may be a bit overlooked today.]
"Dark matter" is the term that physicists use to describe the hypothesized and currently unknown type of matter that is believed to account for a large part of the total mass of the Universe. And one of the best pieces of evidence we have thus far for the existence of dark matter comes from a discovery about the rotation of spiral galaxies made by American astronomer Vera Rubin.
Known as the galaxy rotation problem, the phenomenon describes the discrepancy between the predicted angular motion of galaxies and their observed motion. In our solar system, the further a planet is from the Sun, the slower it travels along its orbit. This fits squarely within the theory of gravity. Similarly, the stars in a spiral galaxy rotate around the center of that galaxy. So it had been expected that the stars further from the center would, like the planets around the Sun, move slower than those nearer to the center.
But what Rubin noticed was that when it comes to spiral galaxies, the speed of stars doesn't change, no matter how far they are from the galactic center. This observation suggests that there is some invisible matter exerting an additional gravitational pull on the more distant stars, causing them to move faster than we would expect them to. Thus, Rubin's discovery stands as the best evidence that "dark matter" does exist. Today, physicists believe that dark matter constitutes 83 percent of all the matter in the universe.
Born in 1928, Rubin was the first female allowed to observe at the Palomar Observatory in San Diego. Today, the 83-year-old astronomer is a researcher in the Department of Terrestrial Magnetism at Carnegie Institution of Washington. The co-author of over 100 peer-reviewed research papers and the author of Bright Galaxies Dark Matters, Rubin is also a member of the US National Academy of Sciences. She is also a member of the Pontifical Academy of Sciences, a scientific academy of the Vatican, founded in 1603 and re-established in 1936 by Pope Pius XI.
"In my own life, my science and my religion are separate," said Rubin in an interview with the National Catholic Register. "I'm Jewish, and so religion to me is a kind of moral code and a kind of history. I try to do my science in a moral way, and, I believe that, ideally, science should be looked upon as something that helps us understand our role in the universe."
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image: Vera Rubin (source: American Institute of Physics, Emilio Segrè Visual Archives, (Wikimedia Commons)