QSO H1821+643 Indicates a Universe Filled with Hydrogen
A quasar slightly depleted of a specific color of light may indicate that our universe is filled with massive amounts of ionized hydrogen . Light from QSO H1821+643, pictured above , comes to us from about a quarter of the way across the visible universe . Detailed analysis now indicates that a tiny amount of this quasar 's light was absorbed by intervening ionized oxygen . Astronomers intuit that this oxygen is surely accompanied by much more abundant ionized hydrogen , which would otherwise be invisible. The oxygen is thus thought to be the tip of a tremendous iceberg , indicating a universe filled with proton and electron clouds so vast they likely exceed the mass of all the stars combined. Still, this is only a small part of the long-sought dark matter astronomers have been searching for. Our universe is thought to be filled with much more abundant, much stranger forms of dark matter .