A team of astronomers from the Service d'Astrophysique du DAPNIA/CEA, in collaboration with scientists of the Padoue Observatory and of the European Southern Observatory (ESO) discovered in a cluster of galaxies an activity of star formation with an intensity which was unsuspected in such an environment.

Using the infrared camera ISOCAM on board the ISO satellite, and the ground based optical Telescope of New Technology (NTT) at La Silla Observatory (Chile), the astronomers disclosed the formation of young stars in the cluster of galaxies Abell 1689 situated at about 2.5 billion light years. The presence of star nurseries hidden in distant clusters, if confirmed, traces a more general change of the properties of clusters with time. This is the first detection of such an evolution in the infrared.