ESA’s orbiting X-ray observatory XMM-Newton has discovered the most massive cluster of galaxies seen in the distant Universe until now. The galaxy cluster is so enormous there can only be a handful of them at that distance, making this a rare catch indeed. The discovery confirms the existence of dark energy. The newly-discovered monster, known only by the catalog number 2XMM J083026+524133, is estimated to contain as much mass as a thousand large galaxies. Much of it is in the form of 100-million-degree hot gas. It was first observed by chance as XMM-Newton was studying another celestial object and 2XMM J083026+524133 was placed in a catalogue for a future follow-up. Georg Lamer, Astrophysikalisches Institut Potsdam, Germany, and a team of astronomers, discovered the record-breaking cluster as they were performing a systematic analysis of the catalog. Based on 3,500 observations performed with XMM-Newton's European Photon Imaging Camera (EPIC) covering about 1 percent of the entire sky, the catalog contains more than 190,000 individual X-ray sources. The team were looking for extended patches of X-rays that could either be nearby galaxies or distant clusters of galaxies. The team have found a cosmic ‘needle in a haystack’.