The ESA said the discovery also confirms the existence of dark energy.

The newly discovered cluster is estimated to contain as much mass as 1,000 large galaxies, with much of it in the form of 100-million-degree hot gas.

Georg Lamer of the Astrophysical Institute in Potsdam, Germany, who led the team that made the discovery, said the cluster is approximately 7.7 billion light-years from Earth.

"Such massive galaxy clusters are thought to be rare objects in the distant universe. They can be used to test cosmological theories," Lamer said. "The existence of the cluster can only be explained with dark energy," he added, noting the cluster contains1,000 times the mass of Earth's Milky Way galaxy.

The discovery is to be detailed in the journal Astronomy & Astrophysics.