Let's start with a definition. Gravity, or gravitational attraction, is the tendency of mass to gather toward itself, drifting together even across great distances due to curvature in spacetime.

Gravity is a force that exists everywhere. It pulls all things with mass or energy toward one another. We commonly experience gravity by being pulled downwards by the Earth. Gravity keeps all of ...

According to the theory of general relativity, a galaxy must have a certain amount of mass to be held together by gravity. However, scientists don’t see enough visible mass in many galaxies in ...