Half the universe’s ordinary matter was missing — and may have been found
At long last, all of the universe’s ordinary matter seems to be present and accounted for. Astronomers have taken a new census of matter in the universe by examining how bright flashes of radio waves from other galaxies, called fast radio bursts, are distorted by particles on their way to Earth. This analysis shows that about half of the universe’s ordinary matter, which has eluded detection for decades, is lurking in intergalactic space, researchers report online May 27 in Nature. The mystery of the missing matter has vexed cosmologists for some 20 years. This elusive material isn’t the invisible, unidentified dark matter that makes up most of the mass in the universe. It’s ordinary matter, composed of garden-variety particles called baryons, such as protons and neutrons (SN: 10/11/17). Observations of light emitted when the universe was young indicate that baryons should make up roughly 5 percent of all the mass and energy in the cosmos. But in the modern universe, all...