The direct measurement of Dark Matter makes it to #8 on Discovery News’ list of the Top 10 Discoveries of the Decade (slideshow). Marusa Bradac, now an assistant professor of physics at UC Davis but then at the Kavli Institute for Particle Astrophysics and Cosmology at the Stanford Linear Accelerator Center, is part of the team that made the discovery back in 2006.
Dark matter is thought to make up about one-fifth of the universe, far more than “ordinary” matter. It is invisible and appears only to interact with other matter through gravity.
Using several light and X-ray telescopes, the team looked at an object called the bullet cluster which is actually made up of two galaxies passing through each other. As they do so, the normal, visible matter gets slowed down, while the invisible dark matter that normally hangs around galaxies goes ahead and can be found by looking for distortions in the light from galaxies in the background.