The amount of matter present in the universe simply hasn’t added up. Astronomers accounting for all the normal matter in the universe that makes up stars, galaxies, and gasses have fallen far short of the amount they should find produced by the Big Bang 13.6 billion years ago.
About 85 percent of the universe is made up of dark matter. The remaining 15 percent is the more conventional kind — much of which builds the things we can see in space, like stars and planets. Of that, about half has been missing from our tally sheet of what makes up the universe.
Now, however, a team of 75 astronomers has finally balanced the cosmological books, so to speak. The missing matter has been hiding out as invisible ionized hydrogen gas, which forms halos around galaxies far larger and more frequently than earlier estimations, according to a report in a physics preprint server, as well as at scientific conferences. The paper will be published in the journal Physical Review Letters.
