2002 Gruber Cosmology The Science

Dr. Vera Cooper Rubin has been a pioneering observer in three areas of modern physical cosmology: the existence and distribution of dark matter in galaxies, the nature and amount of large-scale streaming motions in the universe; and the processes by which the galaxies seen today were assembled.

Perhaps less well known is that several of these things were possible because she was among the very first to adopt a new technology — image tube intensification of spectra — as early as 1965, when the vast majority of astronomers were still using photographic plates.

The best way to measure the mass, hence the dark matter content and distribution of flat galaxies like the Milky Way is to determine how fast they are rotating at different distances from their centers. Rubin began making such measurements in 1964, in collaboration with more senior, photographically inclined, astronomers. A few years later, she was the senior partner using image tubes and later as they became available, CCD detectors. Her observations used the light from gas clouds and stars in galaxies as tracers of the total gravitating mass and showed, first that a large fraction of that mass does not emit or absorb its fair share of light, and second, that the ratio of dark to luminous material gets larger and larger as you look further into the outskirts of galaxies. A 2001 review article (Sofue & Rubin) shows that she is still one of the world's experts in this field.

Rubin has examined motions in the universe and how they deviate from smooth (Hubble) expansion twice. Her master's thesis looked for motions on the scale of the supercluster of galaxies to which we belong. Twenty years later, when she and colleagues announced (at a 1975 meeting) that they had found evidence for motion of our Galaxy and Local Group of galaxies at about 450 km/sec relative to still more distant galaxies, the community was not quite ready for it, and dubbed the result "the Rubin-Ford effect." But her carefully collected data had triumphed over the difficulties of seeing this sort of large scale behavior in the universe and the phenomenon is now called "large scale streaming" rather than "an effect," because it has been confirmed by other careful observations of different sets of galaxies and by a dipole anisotropy in the cosmic microwave background radiation, which reflects our motion relative to the average of the entire observable universe.

In addition, Rubin and a small group of researchers working with her found several of the early examples of galaxies with counter-rotating components, including the only example to date of a galaxy where the two components are of roughly equal mass. Such counter-rotating components are direct observational evidence that a galaxy has captured or merged with another entity (galaxy or gas cloud) with independent dynamics and therefore evidence for the current favored model of how galaxies form, from the assembly of smaller, separate, dwarf galaxies and gas clouds.

Rubin has also been on the front lines of the gradual incorporation of women into modern physical sciences. She was the first woman awarded observing time in her own right at Palomar Observatory, home of the famous 200-inch telescope, and the second woman to receive a Gold Medal from the Royal Astronomical Society (the first was Caroline Herschel, in 1828). Her efforts on behalf of women scientists in the generation following hers have been both untiring and very productive.

Rubin holds degrees from Vassar College (BA), Cornell University (MA), and Georgetown University (PhD), and honorary doctorates from another five institutions, including Harvard and Yale. She and her husband, retired chemical physicist Robert J. Rubin, have four PhD-holding children, including one astronomer, two geologists and a mathematician. Vera is a member of the U.S. National Academy of Sciences and of the Pontifical Academy of Sciences.

By Virginia Trimble
Professor of physics and astronomy
University of California at Irvine and University of Maryland