ISO discovers dust between galaxies

ESA's Infrared Space Observatory (ISO) has made the first direct observations of intergalactic dust. The graph shows faint emissions from cold intergalactic dust rising to a peak in the middle of the Coma Cluster of galaxies as ISO's ISOPHOT instrument scanned across. ISO's scans followed the two tracks plotted across the image. The two measurements gave similar results, which have been averaged to show the signal more clearly. This notable detection may have wide implications for cosmology and the evolution of galaxy clusters. The temperature of the dust is -220 to -240 °C. The cluster's oval appearance, being narrower north-south (top to bottom), was found in an analysis 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 ISO's ISOPHOT scans that this non-circularity is also present in the infrared. Astronomers interpret the Coma Cluster's shape 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 gas winds might be expelling dust from the galaxies. The two large galaxies near the centre of the Coma Cluster have been stripped bare of dust. [Image Date: 1997/11] [97.11.011-001]