Calculations of the expansion of the universe didn’t work. Calculations of the speed of stars in distant galaxies didn’t match what astronomers observed. Calculations of the age of the universe (based on the speed of its expansion) didn’t make sense.
Something had to be wrong with the methods used for these calculations. With these major question marks hanging over the calculations, no one could dependably calculate the history of, present mass of, or future of, the universe. Much of physics research ground to a halt.
Vera Rubin only meant to test a new piece of equipment. What she discovered was that the actual motion of stars and galaxies appeared to prove that Newton’s laws, the most fundamental principles of all of astronomy, were wrong. In trying to explain the difference between observations and Newtonian physics, Rubin discovered dark matter, matter that exists but gives off no light or other radiation that scientists could detect. Astronomers and physicists now believe that 90 percent of the mass of the universe is dark matter.
In 1970 Vera Rubin worked at the Department of Terrestrial Magnetism (DTM) at the Carnegie Institute of Washington. DTM’s director, astronomer Kent Ford, had just created a new high-speed, wide-band spectrograph that could complete eight to ten spectrographs (graphic images on chart paper of some spectrum, in this case of the energy emitted from distant stars at different frequencies along the frequency spectrum) in a single night while existing models were lucky to complete one in a day. Vera was itching to see what Ford’s invention could do.
During the night of March 27, 1970, Rubin focused the DTM telescope on Andromeda, the nearest galaxy to our own. She planned to see whether Andromeda’s millions of stars really moved as existing theory said they should.
When attached to powerful telescopes, spectrographs detect the presence of different elements in a distant star and display what they detect on chart paper. Rubin rigged a high-power microscope to read the charts created by Ford’s spectrograph.
Rubin knew that the marks astronomers measured on a spectrograph shift a tiny bit higher or lower on the frequency chart paper depending on whether the star is moving toward Earth or away from it. This frequency shift is called a Doppler shift. The same kind of shift happens with sound waves as a car passes and the sound of its engine seems to change to a lower frequency. The greater that shift, the greater the object’s speed. Rubin wanted to see if she could use Doppler shifts and Kent’s new spectrograph to measure the speed of stars in distant galaxies.
She found that the stars near the outer edge of Andromeda moved just as fast as the stars near the galaxy’s center. That wasn’t the way it was supposed to be.
Over a period of two months she completed 200 spectrographs. For every galaxy it was the same. The velocities of stars she measured were all wrong. According to every known law of physics, some of those stars were moving too fast for gravity to hold them in their galaxies, and they should fly off into space. But they didn’t.
Rubin was left with two possible explanations. Either Newton’s equations were wrong (something the scientific world would not accept) or the universe contained extra matter no astronomer had detected.
She chose the second explanation and named this extra matter “dark matter” since it could not be seen or detected. Rubin calculated how much dark matter would be needed and how it would have to be distributed throughout the universe in order to make Newton’s equations correct. She found that 90 percent of the universe had to be dark matter.
It took the rest of the scientific community a full decade to grudgingly accept Vera Rubin’s results and the reality that most of the matter in the universe could not be seen or detected by any means available to humans.
However, Vera Rubin’s work in that summer of 1970 changed every calculation and theory about the structure and origins of our universe. It vastly improved astronomers’ ability to correctly calculate the distribution and motion of matter. Meanwhile, luckily, Newton’s laws of motion still survive.
NASA has tried to take a photograph of dark matter (something no once can see or directly detect) by combining X-ray telescope images from the ROSAT satellite with other satellite imagery. It could be the first photo of dark matter.
