The graph shows faint emissions from cold intergalactic dust, which rose to a peak in the middle of the Coma Cluster of galaxies as ESA's Infrared Space Observatory scanned across it. ISO followed the two slanted lines across the image. Both measurements gave similar results, which have been averaged to show the signal more clearly.

Intergalactic dust has never before been observed directly. This notable detection may have wide implications for cosmology and the evolution of galaxy clusters. The temperature of the dust is minus 220 to minus 240 degrees Celsius.

The egg-shaped appearance of the cluster, being narrower in a north-south direction (top to bottom) than in the east-west direction (left to right), was found in an analysis of the Coma Cluster with the German-US-UK Rosat satellite. Contours of X-ray emissions, from gas at 80 million degrees, increase in intensity towards the cluster's centre but are not circular. Some evidence has been found in the ISOPHOT scans, that this non-circularity is also present in the infrared.

Astronomers interpret the shape of the Coma Cluster as evidence that it is colliding and merging with a smaller cluster of galaxies. This collision perhaps explains how the intergalactic dust clouds were created. Fierce winds of gas experienced in the collision of clusters may expel dust from the galaxies. The two large galaxies near the centre of the Coma Cluster have been stripped bare of dust.

CREDITS : ISO graph and scan lines : ESA/ISO, M. Stickel, D. Lemke & ISOPHOT team
Visible-light image : STScI Digitized Sky Survey
X-ray contours : Rosat Data Archive & S. White, A. Vikhlinin