XMM-Newton Finds Missing Intergalactic Material

After a nearly twenty-year long game of cosmic hide-and-seek, astronomers using ESA's XMM-Newton space observatory have finally found evidence of hot, diffuse gas permeating the cosmos, closing a puzzling gap in the overall budget of 'normal' matter in the Universe. While the mysterious dark matter and dark energy make up about 25 and 70 percent of our cosmos respectively, the ordinary matter that makes up everything we see - from stars and galaxies to planets and people - amounts to only about five percent. But even this five percent turns out to be hard to track down. The total amount of ordinary matter, which astronomers refer to as baryons, can be estimated from observations of the Cosmic Microwave Background, which is the most ancient light in the history of the Universe, dating back to only about 380,000 years after the Big Bang. Observations of very distant galaxies allow astronomers to follow the evolution of this matter throughout the Universe's first couple of billions of years. After that, however, more than half of it seemed to have gone missing. "The missing baryons represent one of the biggest mysteries in modern astrophysics," explains Fabrizio Nicastro, lead author of the paper presenting a solution to the mystery.