This image shows a contoured sky map around the galaxy cluster Abell 2218. The red center indicates very hot gas.

The cosmic microwave background – a remnant of the first light in our universe – can be used to track down distant galaxy clusters.

Ricardo Flores is a theoretical astrophysicist at University of Missouri. He talked about the universe shortly after the Big Bang.

Ricardo Flores: The universe was once immersed in a very hot environment, so hot in fact that everything was ionized. There were only elementary particles. And eventually the universe, because of its expansion, was able to cool off and allowed electrons and protons to combine and make atoms.

Flores said that as the universe cooled, its first light came into being some 13 billion years ago. Scientists believe the cosmic microwave background is a remnant of this event.

Astronomers now use this background radiation to detect distant galaxy clusters – groups of 50 to 1,000 galaxies, bound by gravity, filled with hot interstellar gas. As the background radiation passes through a galaxy cluster, its energy is boosted by the hot gas. Ultimately, this energy boost shows up as a shadow in images of the microwave background, indicating the presence of the galaxy cluster.

By finding these clusters and being able to determine properties such as their shape, astronomers are increasingly able to test current theoretical models – testing their ideas about how the universe formed the first stars and galaxies.

Thanks today to Research Corporation, a foundation for the advancement of science.

Our thanks to:
Ricardo Flores
University of Missouri at St. Louis