Although astronomers cannot see dark matter, they can infer its existence in galaxy clusters by observing how its gravity bends the light of more distant background galaxies, a powerful effect called gravitational lensing. The blue streaks near the center of another Hubble image of the cluster are the distorted shapes of more distant galaxies, whose light was bent and magnified by the powerful gravity of Cl 0024+17.This photo is a map of the dark matter that they found, superimposed on a photograph taken by the Hubble space telescope. What is dark matter?
[Dark matter] is an invisible substance composed of atoms that are far different from those that make up the universe’s normal matter, such as stars and galaxies.
In fact, if you drove into a wall made of dark matter, you wouldn’t crack a headlight or inflate an airbag. You wouldn’t even know it happened. But what happens to dark matter during a collision?
Astronomers using NASA’s Hubble Space Telescope got a first-hand view of how dark matter behaves during a titanic collision between two galaxy clusters. The wreck created a ripple of dark matter, which is somewhat similar to a ripple formed in a pond when a rock hits the water.
The ring's discovery is among the strongest evidence yet that dark matter exists. Astronomers have long suspected the existence of the invisible substance as the source of additional gravity that holds together galaxy clusters. Such clusters would fly apart if they relied only on the gravity from their visible stars. Although astronomers don't know what dark matter is made of, they hypothesize that it is a type of elementary particle that pervades the universe.