Measurements made by the Japanese satellite Hitomi before its demise earlier this year reveal a calmatmosphere in the cluster of galaxies in the constellation Perseus, reports a study in this week’s Nature. The satellite, which was launched in February this year, lost ground contact in March and was destroyed.

Clusters of galaxies ? typically consisting of tens to thousands of galaxies bound together by gravity ? are the most massive gravitationally bound objects in the Universe and can therefore provide insight into cosmological parameters and astrophysical processes. These clusters typically contain hot gas (about 107 to 108 kelvin) which emits X-ray radiation. However, little is known about the dynamics of the hot gas.

Andrew Fabian and colleagues, using data from Hitomi, report X-ray observations in the northwestern region of the nucleus of the Perseus galaxy cluster. The data reveal that the core of the Perseus cluster is characterized by a surprisingly quiescent atmosphere, with a velocity dispersion (a measure of the variation in gas velocity) of 164 ± 10 kilometres per second in a region 30 to 60 kiloparsecs from the central nucleus. The authors further report a gradient in velocity of 150 ± 70 kilometres per second across the image of the cluster core. These measurements imply a low level of turbulent pressure for a cluster core region.

“The Perseus observations from Hitomi have given us an important first look at the gas motions in a galaxy cluster, but many more exciting environments and details remain to be explored,” concludes Elizabeth Blanton in an accompanying News & Views article.