
Scientists have developed a technique to use quasars – powerful sources driven by supermassive black holes at the centre of galaxies – to study the Universe’s history and composition. To demonstrate the new method, based on a relation between a quasar’s luminosity at X-ray and ultraviolet wavelengths, they made extensive use of data from XMM-Newton X-ray observatory of the European Space Agency (ESA). This approach promises to become an important tool to constrain the properties of our Universe.