Cosmic Perspectives from Amid the Stars:
Astronomy Blog

Everything you can see and touch is made up of matter. Matter is a fundamental building block of the universe. But, somehow, 85% of it is missing. When we look at all the stars, planets, asteroids, and more in a galaxy, we can calculate its total mass. But mass is the source of gravity. And when we measure the gravitational effects of that same galaxy, we get an entirely different mass. The two methods of determining the mass of a galaxy are at odds with one another.