An international team led by Raphael Gobat and Emanuele Daddi at the Service d'Astrophysique-AIM of CEA-Irfu has discovered the most distant evolved galaxy cluster ever observed at a distance of more than ten billion light-years. The nature and distance of this cluster labelled CL J1449+0856, were determined thanks to the joint use of the ground-based telescopes at VLT (ESO) and of the satellites HST (NASA-ESA) and XMM-Newton (ESA). This discovery shows surprisingly that fully formed large groups of galaxies already existed when the Universe was less than one quarter of its current age.
"A mature cluster with X-ray emission at z = 2.07"
R. Gobat et al. (2011) publié dans Astronomy & Astrophysics ( ficher PDF)
see also : the CEA press release (in french)