A Tour of the Coma Cluster

Narrator (April Jubett, CXC): Many of us have seen intricate patterns that milk makes in coffee and much smoother ones that honey makes when stirred with a spoon. Which of these cases best describes the behavior of the hot gas in galaxy clusters? By answering this question, a new study using NASA's Chandra X-ray Observatory has deepened our understanding of galaxy clusters, the largest structures in the Universe held together by gravity.

Galaxy clusters are comprised of three main components: individual galaxies, multimillion-degree gas that fills the space between the galaxies, and dark matter, a mysterious form of matter that is spread throughout a cluster and accounts for about 80 percent of the mass of the cluster.

A team of astronomers used a new 12-day-long Chandra observation of the Coma galaxy cluster to probe its hot gas, which glows only in X-ray light. By measuring the behavior of the hot gas on small scales, the researchers were able to learn about the viscosity — the technical term for stickiness — of the hot gas in Coma. They found that the viscosity of Coma's gas was lower than they expected. In other words, the hot gas in Coma behaves more like milk than honey in our cosmic coffee mug.

Why is the viscosity of Coma's hot gas so low? Scientists are still working on that question, but one possible explanation is that tiny irregularities in Coma's magnetic field create turbulence in the hot gas. These small-scale properties can, in turn, have major impacts on important phenomena such as collisions and mergers with other galaxy clusters and galaxy groups. Scientists will continue to study galaxy clusters with Chandra to get a deeper understanding of these cosmic giants.