COMMENT OBITUARY Vera Rubin (1928–2016) Observational astronomer who confirmed the existence of dark matter.

era Cooper Rubin was a which was not recognized until many pioneering astronomer, an years later. admired role model and a After teaching at Georgetown, Vera Vpassionate champion of female scien- accepted a research position in 1965 at tists. Her groundbreaking work con- the Carnegie Institution’s Department firmed the existence of dark matter of Terrestrial Magnetism in Washing- and demonstrated that galaxies are ton DC, where she remained for the rest embedded in dark-matter halos, which of her career. There she conducted her we now know contain most of the mass groundbreaking research with Ford, in the Universe. and mentored generations of young OF WASHINGTON INSTITUTION CARNEGIE In the 1970s, Rubin showed that the astronomers in the investigation of speed at which stars orbit around the galaxy dynamics and dark matter. She centres of spiral galaxies remains high was deeply loved and admired by all even at the outskirts. This contradicts who knew her. the Newtonian theory of gravitation, In spite of the numerous obstacles which predicts that the speeds of dis- she faced as a female scientist, Rubin tant stars should fall off as the pull of triumphed. She was always cheerful, gravity declines, just as the farthest passionate and persistent. She had planets in the Solar System orbit more wanted to attend graduate school at slowly around the Sun than do closer Princeton University in New Jersey, ones. The discrepancy is striking — if but was denied because the univer- Jupiter moved at the same rate as Earth, sity did not accept women at the time for instance, it would orbit the Sun (Princeton awarded Rubin an honorary every 5 years, rather than every 12. degree in 2005). She wanted to use the The only plausible explanation for these wavelengths. This avoided the difficulties of Hale telescope at the Palomar Observatory galactic ‘flat rotation curves’ (named interpreting gas dynamics that might affect in California, but was denied because the for their shape on a graph) was that the other studies. Their confirmation in 1978 of facility did not allow women to do so until mass of the galaxies must extend invis- flat rotation curves in a large sample of ten the 1960s. She paved a path for women not ibly beyond the most distant stars and gas spiral galaxies confirmed the existence of only by encouraging and inspiring them, but clouds. That excess mass is known as dark dark matter (V. C. Rubin et al. Astrophys. J. also by pressing for them to be hired for fac- matter. Its existence was first suggested Lett. 225, L107–L111; 1978). ulty positions, to be awarded honours and to in 1933 by astronomer Fritz Zwicky, who Vera Rubin passed away on 25 December be invited to speak at conferences. If too few saw that galaxies in clusters moved more 2016, aged 88. She was born in Philadelphia, women were listed as speakers, she would quickly than would be predicted from Pennsylvania, in 1928 and moved with her demand that organizers add more. As Vera observable mass. family to Washington DC when she was liked to say, “Worldwide, half of all brains Dark matter, which neither emits nor 10. Her fascination with the night sky was are in women.” absorbs light, makes up 85% of the mass- evident at an early age. She would peer out Vera’s accomplishments have been rec- density of the Universe. We don’t know of her bedroom window and wonder what ognized by numerous honours, including what it is for sure, but most astrophysicists caused the stars to move across the sky, or the US National Medal of Science, the Gold think that it must be a new kind of particle, why the Moon seemed to follow her as she Medal of the Royal Astronomical Society in different from the familiar baryons (such as rode in the back seat of her parents’ car. London, the Gruber Foundation Cosmol- protons and neutrons) in stars, planets and Her insatiable desire to understand the ogy Prize, the James Craig Watson Medal of people. The nature of dark matter is one Universe led her to study at Vassar College the US National Academy of Sciences and of science’s great unsolved mysteries. The in New York state, which she chose because many honorary degrees. She was widely seen answer will change how we think about the the first professional female astronomer as deserving of a Nobel prize for her pivotal Universe. in the United States, Maria Mitchell, had observations. Vera’s legacy as the ‘mother’ Rubin made her discovery by working taught there in 1865–88. Rubin graduated of flat rotation curves and dark matter will closely with her colleague Kent Ford, who in 1948 as the only astronomy major in her be forever remembered, as will her role in built the sophisticated optical spectrograph class, and was married the same year. She mentoring and inspiring generations of needed for such accurate measurements. In earned her master’s degree at Cornell Uni- scientists, male and female. ■ 1970, they published their first rotation curve versity in Ithaca, New York, then moved for the nearby Andromeda galaxy (V. C. with her husband to Washington DC, where Neta A. Bahcall is a professor of astrophysics Rubin and K. Ford Astrophys. J. 159, 379; she received her PhD from Georgetown at Princeton University, New Jersey, and chair 1970). Instead of observing hydrogen gas in University in 1954. Her PhD thesis demon- of the astronomy section of the US National galactic disks at 21-centimetre radio wave- strated that galaxies are clumped rather than Academy of Sciences. She was Vera Rubin’s lengths, as others had done, Rubin and Ford evenly distributed in space — a surprising close friend and colleague for many years. chose to use spectral signatures at optical and crucial finding, the importance of e-mail: [email protected]

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