A rotation curve is a plot of the rotational velocity of a galaxy as a function of the distance away from the galactic center. Predictions for rotation curves for spiral galaxies suggest that the curve should decline beyond the galactic bulge. Actual measurements, however, show that the rotation curve is flat beyond the bulge. What does this deviation from prediction state about spiral galaxies, including the Milky Way?

Question

Quizplus · Accepted Answer

The flat rotation curves of spiral galaxies, contrary to the expected decline, indicate the presence of a significant amount of unseen mass, or dark matter, surrounding the visible parts of these galaxies. This unseen mass exerts gravitational force, affecting the rotation speeds of stars and gas clouds at the outer edges of galaxies, keeping them higher than would be expected if only visible matter were present.

A Rotation Curve Is a Plot of the Rotational Velocity