Page "Dark matter" Paragraph 18

After Zwicky's initial observations, the first indication that the mass to light ratio was anything other than unity came from measurements made by Horace Babcock.

In 1939, Babcock reported in his PhD thesis measurements of the rotation curve for Andromeda which suggested that the mass-to-luminosity ratio increases radially.

He, however, attributed it to either absorption of light within the galaxy or modified dynamics in the outer portions of the spiral and not to any form of missing matter.

Then, in the late 1960s and early 1970s, Vera Rubin, a young astronomer at the Department of Terrestrial Magnetism at the Carnegie Institution of Washington, presented findings based on a new sensitive spectrograph that could measure the velocity curve of edge-on spiral galaxies to a greater degree of accuracy than had ever before been achieved.

Together with fellow staff-member Kent Ford, Rubin announced at a 1975 meeting of the American Astronomical Society the discovery that most stars in spiral galaxies orbit at roughly the same speed, which implied that their mass densities were uniform well beyond the locations with most of the stars ( the galactic bulge ), a result independently found in 1978.

An influential paper presented these results in 1980.

Rubin's observations and calculations showed that most galaxies must contain about ten times as much “ dark ” mass as can be accounted for by the visible stars.

Eventually other astronomers began to corroborate her work and it soon became well-established that most galaxies were in fact dominated by " dark matter ":