Dark Matter: It exists!

A remarkable new image was revealed yesterday that constitutes strong new evidence for dark matter:


Dark matter is matter which makes up the bulk of the mass of the universe, but which has escaped detection by conventional means. It's required because observations of things like the rotational speeds of galaxies and orbital velocities of galaxies in clusters, Gravitational lensing of background objects by galaxy clusters and the temperature distribution of hot gas in galaxies and clusters of galaxies don't make sense unless there is additional, undetected mass. Dark matter also plays a central role in galaxy evolution and has measurable effects on the anisotropy of the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation.

Unfortunately, because it doesn't interact with electromagnetic radiation, it's hard for us to see directly - we can only infer its presence via gravitational effects. That's what the new study, to be published in Astrophysics Journal, has done.

Astronomers using NASA's Hubble Space Telescope have discovered a ghostly ring of dark matter that formed long ago during a titanic collision between two massive galaxy clusters. 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.

This Hubble composite image shows the ring of dark matter in the galaxy cluster Cl 0024+17. The ring-like structure is evident in the blue map of the cluster's dark matter distribution. The map was derived from Hubble observations of how the gravity of the cluster Cl 0024+17 distorts the light of more distant galaxies, an optical illusion called gravitational lensing. Although astronomers cannot see dark matter, they can infer its existence by mapping the distorted shapes of the background galaxies. The map is superimposed on a Hubble Advanced Camera for Surveys image of the cluster taken in November 2004.

This ring will prove important to astronomers for many reasons. This is the first time a dark matter halo has been discovered that's different in shape from the other mass in a cluster, and it will allow researchers to make better predictions of how dark matter behaves, and how it can be shaped by normal matter. Plus, the image is just way cool!