Page 10, Cosmology: [Previous Page] [Next Page] [Class Home Page] Text Pages 425-427

We've already discussed Dark Matter in the class Here and in subsequent pages. However, we see now, if we want to determine the eventual fate of our universe, we must somehow measure ALL MASS, and that includes the Dark Matter.

One of the ways astronomers have been able to measure the total mass in our universe, including Dark Matter, is through Gravitational Lensing. Sometimes we see MULTIPLE images of distant objects. The foreground object's mass (a galaxy here), bends the light path, creating the images:



We see incredible gravitational lensing in the direction of Clusters of Galaxies. This is seen in the image below. The amount of mass seen in visible matter is not enough to bend the light, meaning the DARK MATTER associated with the cluster makes up more than 90% of the mass!



ALL THE BLUE ARCHES are from the exact same galaxy! How do we know? When we look at the light of each of the blue arches, they all have the EXACT SAME SPECTRUM.