However, when astronomers add up all the mass of normal matter in the universe, a third of it can’t be found. (This missing matter is distinct from the still-mysterious dark matter.) However, the matter might be contained in gigantic strands of hot gas in intergalactic space, which are invisible to optical light telescopes. Data from Chandra X-ray Observatory and other telescopes are on the case: https://go.nasa.gov/2N7nWj6