Clues to the Growth of One of the Universe's Largest Structures Revealed

The discovery of enormous arms of hot gas located in the Coma cluster of galaxies reveals new insight into how the cluster has formed over the years, growing through the merger of smaller groups and clusters of galaxies before becoming one of the largest structures in the universe held together by gravity.

The finding, made using NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton, points toward a process through which smaller galaxy clusters' gas was stripped away by the head wind created by the cluster's motion through hot gas, causing the arms currently observed to form.

Coma is unusual in that it contains two giant elliptical galaxies near its center, both of which are likely left over from the two largest clusters that merged with Coma in the past, the scientists report in the study detailing their discoveries.

Based on their length and the speed of sound in hot gas, the researchers estimate the arms to be some 300 million years old. This and the fact that they are smooth in shape offers additional clues regarding the conditions of the hot gas found in Coma, suggesting a relatively calm environment despite its many mergers.

What small amount of turbulence does exist in Coma is likely the result of large-scale magnetic fields, the scientists hypothesize, though estimating just how turbulent a galaxy cluster is can be a challenge for astrophysicists: at this point researchers have come up with a range of answers, though some of the conflict, suggesting the need for more research.

Observations of the new arms reveal two of them appear to be connected to a group of galaxies located roughly 2 million light-years from Coma's center. At least one of these arms connects to a larger structure and spans some 1.5 million light-years at least. Finally, researchers have been able to detect a slight tail behind one of the galaxies of Coma -- likely evidence of gas being stripped from a galaxy as well as the groups or clusters that have merged there.