September 23, 2023
The "problem" of spiral galaxy rotation and dark matter
When Vera Rubin used spectroscopy to measure the rotation speed of matter in spiral galaxies around their center of mass, it came as a surprise to many scientists of her time.
The angular velocity of the arms of a spiral galaxy was nearly the same at all distances from its center of mass. This sharply contrasted with the angular velocity of planets orbiting the Sun, where both angular and linear velocities decrease with increasing distance.
Is this a problem from a physics perspective? Let's explore it together.
Orbital velocity is the speed at which an object on a circular orbit experiences gravitational force equal to the centrifugal force pushing it away.