NEW YORK — E. Margaret Burbidge, an astrophysicist who made pathbreaking findings about the state of the cosmos, not the least of which was discovering precisely what it entailed to succeed as a woman in a male-dominated universe at midcentury, died Sunday at her home in San Francisco. She was 100.

Her daughter, Sarah Burbidge, said the cause was complications from a fall.

A native of England who worked largely in the United States, Ms. Burbidge built a career that was stellar in both senses. She was considered one of the foremost astronomers in the world, long regarded as a trailblazer for women in the field.

Ms. Burbidge was the first woman to serve as director of the Royal Observatory, the storied British institution. She was also a contributor to the design of instruments carried aboard the Hubble Space Telescope and a recipient of the National Medal of Science, bestowed in 1985 by President Ronald Reagan.

“She has a huge imprint on the history of modern astronomy and cosmology and nuclear astrophysics,’’ George Fuller, a theoretical astrophysicist at the University of California San Diego, where Ms. Burbidge taught for many years, said in an interview for this obituary in 2017.

Ms. Burbidge had made her reputation by studying stars, often in collaboration with her husband, astronomer Geoffrey Burbidge. Their research included a landmark article describing the formation within stars of nearly all the chemical elements — those incumbents of the periodic table that are the stuff of life in the universe.

She also studied the properties of galaxies and the nature of quasars and in later years came to question the Big Bang Theory, the cornerstone of modern cosmology.

Her achievements were all the more noteworthy for having been made in a discipline that was a time-honored bastion of swaggering masculinity. It was a field in which, early in her career, she was denied access to the very instrument an observational astronomer needs most: a telescope.

Eleanor Margaret Peachey was born in Davenport, in northwest England.

“I was born on Aug. 12, 1919, a date which, at age 11 or 12, when I had been given a much bowdlerized account of the ‘facts of life’ by my mother, struck me as a weird and wonderful coincidence: The beginning of my existence as a few-celled creature must have coincided with the World War I armistice, Nov. 11, 1918,’’ Ms. Burbidge wrote in a 1994 autobiographical essay in The Annual Review of Astronomy and Astrophysics.

She added, “My excitement in telling my mother this deduction was not greeted with enthusiasm nor with any further explanation.’’

But her family encouraged scientific curiosity in other respects. Her father, Stanley Peachey, was a chemistry lecturer; her mother, Marjorie (Stott) Peachey, had been his student.

When Margaret was a small child, the family moved to London, where Stanley Peachey pursued a career in industrial chemistry. He earned several lucrative patents, including one for a process that streamlined the vulcanization of rubber.

At 4, crossing the English Channel with her family at night for a holiday in France, Margaret looked heavenward and was smitten.

“It’s the first time I really noticed the stars,’’ Ms. Burbidge recalled in a 1978 oral history interview. “A small child brought up in London doesn’t get to see much of the sky, because it’s so often cloudy.’’

She entered University College London in 1936 and studied astronomy, physics, and mathematics, graduating with first-class honors in 1939. She stayed on for graduate work at its parent institution, the University of London, earning a PhD there in 1943.

During the war, she worked as the caretaker of the telescope at the university’s observatory, a job normally done by men. She used the opportunity to carry out her own observational research: London’s wartime blackouts made the stars more accessible than they had been in years.

She married Geoffrey Burbidge, a University of London graduate student, in 1948. Inspired by her, he switched from physics to astronomy.

In the late 1940s, seeking better telescopes and clearer skies, Margaret Burbidge applied for a fellowship from the Carnegie Institution for Science. The award would have let her work at Mount Wilson Observatory, near Pasadena, Calif.

Her application was declined. Women, she was informed, were not permitted to use Mount Wilson’s telescopes.

“The situation for women in astronomy has changed dramatically in my lifetime,’’ she told The San Francisco Chronicle in 2005. “Young women now are very surprised to learn that women were once not allowed on Mount Wilson and that men making the rules somehow developed the idea that the wives of the astronomers would not like the thought of their men working with women ‘during the night!’ ’’

She managed to gain access to Mount Wilson some years later but only by posing as her husband’s assistant. The couple was obliged to live in a rustic, unheated cottage on the mountain, a far cry from the heated accommodations, complete with resident chef, in which the male astronomers were housed.

Over the years, Ms. Burbidge also worked at the California Institute of Technology; the Harvard College Observatory; Yerkes Observatory, the University of Chicago’s facility in Williams Bay, Wis.; and the McDonald Observatory, near Fort Davis, Texas, now operated by the University of Texas Austin.

She joined the University of California San Diego in the early 1960s and went on to become the first director of its Center for Astrophysics and Space Sciences. At her death, she was university professor emeritus there.

With her husband, American physicist William Fowler, and English astronomer Fred Hoyle, Ms. Burbidge wrote a 1957 article that is considered one of the most influential scientific papers of its era. Titled “Synthesis of the Elements in Stars,’’ but known in astronomical circles simply as B2FH, it was published in the journal Reviews of Modern Physics.

In it, the authors argued that nearly all of the chemical elements, from aluminum to zinc, are forged in the bodies of stars, a process now called stellar nucleosynthesis.

It was already known that the lightest elements, like hydrogen and helium, had been created amid the Big Bang. But the origin of the heavier elements, including the carbon that makes up plants and animals, the oxygen in the atmosphere, and the gold and silver mined from the ground — in sum, the very matter of the universe — was the subject of longstanding debate.

The thesis of B2FH, now widely accepted, is that the heavier elements are synthesized from the lighter ones by thermonuclear reactions within stars. Loosed into space, these elements can also recombine to form new stars, beginning the cycle once more.

As the article describes it, we are all, in essence, made from stars.

“That work laid the foundations for all of modern nuclear astrophysics, and particle astrophysics as well,’’ Fowler said. “It gave a blueprint for how the elements were formed in the cosmos.’’

Ms. Burbidge, a naturalized American citizen, was the first woman to serve as president of the American Astronomical Society, a post she held from 1976 to 1978. She was also a past president of the American Association for the Advancement of Science.

Her other laurels include the Helen B. Warner Prize from the American Astronomical Society, shared with her husband, and the Catherine Wolfe Bruce Gold Medal from the Astronomical Society of the Pacific.

She had an asteroid named for her, Minor Planet 5490 Burbidge.

Geoffrey Burbidge died in 2010. In addition to her daughter, Margaret Burbidge leaves a grandson.