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. The trouble is that ordinary detectors turned sharp emission lines into blurry smudges, and the individual "voices" of the streams merged into one indistinct chorus.

A new instrument, the Resolve microcalorimeter on the Japanese XRISM satellite, works like an ear capable of picking out every note in a chord. It measures the energy of each photon to within 4.5 electronvolts at an energy of 6000 electronvolts. That is like hearing a half-tone difference against the backdrop of an orchestra. When the instrument was pointed at the cluster's center, distinct peaks emerged in the iron line: one main peak, a second slightly shifted toward the red edge, and a third with a strong shift toward the blue. A blue shift means the gas is flying toward us at about 1274 kilometers per second.

Astronomers ran a blind search: they decomposed the spectrum into 51 possible components with a step of 3 electronvolts and checked which of them were not random. In the center they found a stream flying toward us at about 1150 km/s, and in the southern part a stream receding at 1250 km/s. Most intriguingly, these speeds nearly match the speeds of groups of galaxies seen with optical telescopes. It turns out that the gas and the galaxies move together, like musicians in one section of an orchestra.

Now that we have learned to distinguish individual parts in the X-ray orchestra, we can ask new questions. Exactly how does the energy of mergers turn into heat and turbulence? Why does the radio halo live so long? Future XRISM observations will add new voices to this score, and perhaps we will finally hear the Coma Cluster rehearsing its cosmic symphony.