Bullet Cluster

The Bullet Cluster is a pair of galaxy clusters that collided, providing key evidence for dark matter. During the collision, the hot gas in the clusters interacted and slowed down, while the majority of the mass, thought to be dark matter, passed through without much interaction. Observations from X-ray emissions and gravitational lensing showed that the visible matter (gas) and the mass (including dark matter) were separated. This separation supports the idea that most of the universe's mass is dark matter, which does not emit light, unlike normal matter such as stars and gas.