The observation that outer parts of galaxies rotate faster than the observable mass within their orbit can pull them implies that _____________.
A) galaxies are unstable
B) all galaxies will eventually develop a bulge
C) In time, galaxies will develop spiral arms
D) the masses of galaxies are larger than their luminous mass
E) None of these choices is correct.

Question

Quizplus · Accepted Answer

The faster rotation of the outer parts of galaxies suggests the presence of additional, unseen mass, indicating that galaxies have more mass than what is visible, often attributed to dark matter.

The Observation That Outer Parts of Galaxies Rotate Faster Than