WASHINGTON — Vera Rubin, an astronomer who helped prove the existence of dark matter, one of the fundamental principles in the study of the universe, but who battled sex discrimination throughout her career, died Dec. 25 at an assisted living facility in Princeton, N.J. She was 88.
She had dementia, said a son, Allan.
Dr. Rubin’s groundbreaking discoveries, made primarily with physicist W. Kent Ford, have revolutionized the way scientists observe, measure, and understand the universe.
The concept of ‘‘dark matter,’’ an undetermined substance among stars in distant galaxies, had existed since the 1930s, but it was not proved until Dr. Rubin’s studies with Ford in the 1970s. It is considered one of the most significant and fundamental advances in astronomy during the 20th century.
‘‘The existence of dark matter has utterly revolutionized our concept of the universe and our entire field,’’ University of Washington astronomer Emily Levesque told Astronomy magazine this year. ‘‘The ongoing effort to understand the role of dark matter has basically spawned entire subfields within astrophysics and particle physics.’’
Dr. Rubin, who spent most of her career at the Carnegie Institution of Washington, D.C., continued to make new discoveries — including of previously unknown galaxies — into the 21st century. For years she was considered a leading contender for the Nobel Prize, but the award never came. Many attributed the oversight to gender bias among male scientists and prize committees.
The last woman to win a Nobel Prize in physics was Maria Goeppert Mayer, who shared the 1963 prize for her work on atomic structure. The only other woman to win a Nobel in physics was Marie Curie in 1903.
‘‘Alfred Nobel’s will describes the physics prize as recognizing ‘the most important discovery’ within the field of physics,’’ Levesque told Astronomy magazine. ‘‘If dark matter doesn’t fit that description, I don’t know what does.’’
Growing up in Washington, Dr. Rubin built a rudimentary telescope out of a cardboard tube.
Early in her career, she made discoveries that challenged accepted theories in astronomy, but she was seldom taken seriously by other astronomers, most of them male. When she applied to graduate school at Princeton University in the late 1940s, she was flatly told, ‘‘Princeton does not accept women.’’
Dr. Rubin forged ahead, ultimately receiving a doctorate from Georgetown University while raising four children.
She struggled to gain admittance to leading observatories. In 1964, she became the first woman to receive formal approval to use the Palomar Observatory in Southern California.
When she arrived, she discovered that it did not have a women’s restroom.
‘‘She went to her room, she cut up paper into a skirt image, and she stuck it on the little person image on the door of the bathroom,’’ astrophysicist Neta Bahcall told Astronomy magazine. ‘‘She said, ‘There you go; now you have a ladies’ room.’’’
While fighting these battles on Earth, Dr. Rubin peered into the cosmos and examined the rotation of more than 200 galaxies. Among other findings, she determined that stars orbiting on the outer edges of galaxies moved at the same speed as those near the interior.
The discovery defied the accepted norms of astronomy, which held that the far-flung stars should move more slowly. To account for the uniform speeds, Dr. Rubin concluded that the distant regions of galaxies contained considerable amounts of a dense, unseen mass, or dark matter, which affected everything from gravitational pull to the shape of galaxies to how stars move in relation to one another.
Although its precise composition remains unknown, scientists think that about 84 percent of the cosmos is made up of dark matter.
‘‘So important is this dark matter to our understanding of the size, shape, and ultimate fate of the universe,’’ Dr. Rubin wrote in Scientific American in 1998, ‘‘that the search for it will very likely dominate astronomy for the next few decades.’’
Vera Florence Cooper was born July 23, 1928, in Philadelphia. She moved with her family to Washington when she was 10. Her father was an electrical engineer.
She was the only astronomy major to graduate from Vassar College in 1948. When she sought to enroll as a graduate student at Princeton, she learned women were not allowed in the university’s graduate astronomy program, so she instead earned her master’s degree from Cornell University.
She taught at Montgomery College and later at Georgetown before joining the Carnegie Institution, a Washington-based research center, in 1965.
Dr. Rubin published more than 100 scientific papers and was on the editorial boards of professional journals and Science magazine. She published a collection of essays, ‘‘Bright Galaxies, Dark Matters,’’ in 1997. In 1993, she received the nation’s highest scientific award, the National Medal of Science.
Her husband of 59 years, Robert Rubin, a physical chemist, died in 2008. All four of their children received doctorates in science or mathematics. A daughter, astronomer Judy Young, died in 2014.
Dr. Rubin leaves three sons, David, a geologist, of Santa Cruz, Calif., Karl, a mathematician, of Irvine, Calif., and Allan, a geologist, of Princeton; a sister, Ruth Burg of Washington; five grandchildren; and a great-granddaughter.