In the 1970s, Vera Cooper Rubin started what seemed like an innocent experiment with another American astronomer, Kent Ford.
Rubin wanted to determine why spiral galaxies differ in structure.
She decided to compare the movements of stars near the center of a galaxy with those in the outer reaches of the galaxy.
Rubin chose the Andromeda galaxy for her first experiment and conducted spectrum analysis of different parts of the galaxy.
Most astronomers assumed that the mass or matter of a galaxy was concentrated in the center of the galaxy because that’s where most of the light appears.
According to Newton’s laws of gravity, the stars near the inside of the galaxy should therefore move much faster due to the extra gravitational pull of the extra matter.
Much to their surprise, Rubin and Ford found that the stars in the outer reaches of Andromeda were moving at the same speed as the inner stars.
They immediately tested other galaxies and found the same results. In some cases, the speed of the outer stars was actually higher. They were moving fast enough to escape the galaxy’s gravity, but that was not occurring.
Rubin knew that there was only one possible conclusion, and it also explained her earlier findings on the additional movements of some galaxies.
The distribution of light in a galaxy has nothing to do with the distribution of matter. Instead, there are large amounts of mass in the universe that we cannot see.
It is called dark matter, and it is the gravity from this dark matter that affects the outer stars of the galaxies.
Rubin has analyzed over 200 galaxies. She estimates that 90 percent of the universe might be made up of this invisible matter. What is this dark matter? It remains a mystery for future astronomers to solve.
Kent Ford built a spectrograph that could photograph a galaxy’s spectrum 10 times faster than the previous spectrographs.