The intergalactic gas detected by Rosat has a temperature of 80 million degrees, far hotter even than the core of the Sun. The gas is extremely tenuous, so it cannot simply warm the grains of dust like a hair-drier. Instead the hot gas subjects the dust to impacts by energetic atomic particles which knock atoms out of it, and so gradually erode the dust grains. Calculations suggest that the hot gas will destroy the cold dust in about 100 million years. Although that is very slow by human standards, it represents only one-hundredth of the age of the galaxies.
Experts therefore have to consider where fresh supplies of intergalactic dust come from.
Rosat astronomers found that the Coma Cluster is not spherical, which would be the shape expected in an isolated cluster. The same shape is apparent in the intergalactic dust cloud observed by ISO at long infrared wavelengths. A smaller cluster of galaxies is colliding with the large Coma Cluster and altering its shape. The two largest galaxies in the middle of the Coma Cluster do not show up in our infrared scan. They've lost their dust, either in collisions between galaxies or more probably in the merger of the Coma Cluster with another cluster.