Nhut Truong

Every galaxy is wrapped in an invisible shell of hot gas, like steam rising from a pot of boiling water. This gas barely glows in X-rays, making it notoriously difficult to measure. Yet it holds the memory of stellar explosions and the galaxy's growth. The new method uses light from a galaxy's bright center.

A giant cauldron of simmering soup stretches across millions of light-years. This is the atmosphere of the Perseus galaxy cluster — a cloud of scorching gas held together by gravity. Until recently, astronomers thought that in the center of this cauldron, the gas was calmly cooling, ready to condense into new stars.

The Perseus galaxy cluster is a giant metropolis of thousands of star islands, bathed in an invisible ocean of scorching gas. Like urban smog, this gas preserves traces of all the chemical factories that have operated in galaxies for billions of years: supernova explosions that scatter freshly forged atoms across the surroundings.

An orchestra of hundreds of galaxies performs a symphony in X-rays, but until recently we heard only a general hum. The Coma Cluster is about a thousand galaxies immersed in a cloud of scorching gas at a temperature of one hundred million degrees. This gas glows in X-rays, and its spectrum tells us how it moves.