U.S. Department of Energy

Pacific Northwest National Laboratory

Dark Matter

In 1933, Fritz Zwicky, a faculty member of Caltech, coined the term “dark matter” to describe the unseen matter that must dominate the Coma Galaxy Cluster in order to match his observations of the motion of its galaxies. Scientists have been confident dark matter exists for more than 80 years, although they’re still trying to understand what it’s made of and why there seems to be so much of it. Dark matter is the gravitational glue that holds stars and gas in galaxies and great galaxy clusters together, whose fast-moving stars would otherwise be flung far apart. It is a form of matter that does not emit light and, therefore, is difficult to detect with ordinary observation methods. Scientists know it must exist, because its mass causes gravitational effects that can be observed. Based on the effects of gravity in our galaxy, scientists believe there is a high concentration of dark matter near the galaxy’s center around the supermassive black hole residing there.

| Pacific Northwest National Laboratory