We know that spiral galaxies contain dark matter because the gas in the disk rotates with a velocity that decreases in a way that is similar to our Solar System.

Question

Quizplus · Accepted Answer

The velocity of gas in the disk of spiral galaxies remains relatively constant or even increases with distance from the center, unlike the Solar System where velocity decreases with distance. This discrepancy suggests the presence of dark matter.

We Know That Spiral Galaxies Contain Dark Matter Because the Gas