Galaxy cluster measurements can reveal not just how structures grew, but also how their growth was impeded by dark energy \u2014 the thin glaze of repulsive energy that permeates space, accelerating space\u2019s expansion and thereby separating matter.<\/p>\n

If dark energy is the energy of space itself, as the standard model of cosmology assumes, then it will have a constant density throughout space and time (that\u2019s why it\u2019s sometimes referred to as the cosmological constant). But if its density is instead dropping over time, then it\u2019s something else entirely. \u201cThat\u2019s the biggest question that cosmology has,\u201d said Sebastian Grandis, an eRosita team member at the University of Innsbruck in Austria.<\/p>\n

From their map of thousands of clusters, the researchers found that dark energy matches the profile of a cosmological constant, although their measurement has a 10% uncertainty, so an ever-so-slightly varying dark energy density remains possible.<\/p>\n

Originally, eRosita, which sits aboard a Russian spacecraft, was to conduct eight full-sky surveys, but in February 2022, weeks after the telescope began its fifth survey, Russia invaded Ukraine. In response, the German side of the collaboration, which operates and runs eRosita, put the telescope into safe mode, ceasing all scientific observations.<\/p>\n