The evidence for dark matter

Dark matter is matter that does not give off, absorb, or reflect light, and is detected only through its gravity. Several independent lines of indirect evidence point to it. In the 1930s Fritz Zwicky found that galaxies in the Coma Cluster move too fast to be held together by the gravity of the visible matter alone. In the 1970s Vera Rubin and others found that stars and gas in the outer parts of spiral galaxies orbit about as fast as those closer in, when they should orbit more slowly if most of the mass were in the visible stars; this suggests each galaxy sits inside a much larger halo of unseen mass. Gravitational lensing, the bending of light from distant galaxies by the gravity of foreground clusters, reveals far more mass than the clusters' visible stars and gas, and in colliding clusters like the Bullet Cluster the lensing mass is found separated from most of the ordinary gas. Patterns in the cosmic microwave background also require it. Dark matter makes up about 85 percent of all the matter in the universe, but what it actually is remains unknown, and it has not yet been detected directly.

This explanation is AI-generated and can occasionally be wrong. 🚩 Report