Pioneering astronomer Vera Rubin dies at 88

As a woman, astrophysicist Vera Rubin had to fight just to get access to a telescope. What she saw when she did further rattled conventions: galaxies that were rotating more quickly than predicted by the laws of physics.

This movement, she concluded, could be explained if the universe was filled with a type of mass that no one had ever seen, mysterious stuff that came to be known as dark matter.

Her once-startling theory is now an accepted part of the still-evolving story of the universe. Finding firm evidence of dark matter stands as the seminal achievement of a scientist known for breaking barriers and helping others to build on such work.

Rubin died Sunday at 88 in the Princeton, N.J., area after a long period of declining health, according to family and colleagues. She worked for decades at the Carnegie Institution for Science, headquartered in Washington, D.C.

Although dark matter hasn’t been directly observed, scientists widely accept that it makes up about 27 percent of the universe. That makes it far more abundant than the normal matter that makes up the stars, planets and everything else we can observe, which total 5 percent. (The bulk of the universe is thought to be made of another mysterious thing called dark energy.)

The concept of dark matter, though long proposed, had limited evidence behind it in the 1970s as Rubin and colleague Kent Ford were studying the subtleties of dim light reaching Earth from distant galaxies across nearly fathomless expanses of space.

They used spectroscopy to examine how quickly galaxies revolved: The light became bluer as one side of a galaxy rotated toward them (compressing the electromagnetic waves) and redder as the other side rotated away (causing the waves to stretch out). But the outer reaches of the galaxies were turning much too fast, according to the physics of gravity. Their rotation should have been much slower if they had only the small amount of mass that they appeared to contain.

This conundrum disappeared, however, if there was much, much more mass in these galaxies, mass that did not emit light and therefore was seemingly invisible, Rubin and Ford theorized in a 1978 paper. Other scientists were reaching similar conclusions through studies of radio waves.