How do you see the invisible? By looking for its effects on the visible. Astronomers have put this method to use in looking for Dark Matter. Earlier this year, they found strong evidence of Dark Matter in a remarkable cosmic structure called the ‘bullet cluster’.
The bullet cluster’ is actually two clusters of galaxies are actually passing through one another. As the two clusters cross at a speed of 10 million miles per hour, the luminous matter in each cluster interacts with the luminous matter in the other cluster and slows down. But the dark matter in each cluster does not interact at all, passing right through without disruption. This difference in interaction causes the dark matter to sail ahead of the luminous matter, separating each cluster into two components: dark matter in the lead and luminous matter lagging behind.
The image above is a composite of visual imagery, x-ray imagry, and the mass of the structure as calculated by gravitational lensing.
“This is the most energetic cosmic event, besides the Big Bang, which we know about,” said team member Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.