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LONDON — Astrophysicists are mystified after concluding that 80% of the light in the universe appears to be missing.

The total amount of light in the universe can be measured by tracking changes in hydrogen after exposure to ultraviolet light. The hydrogen becomes ionized and can be seen on large telescopes.

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A study in Astrophysical Journal Letters claims that the amount of ionized hydrogen suggests there is far more ultraviolet light in the universe than can be accounted for – five times too much, in fact. The ultraviolet light could be coming from an “exotic new source”, scientists suggest.

Juna Kollmeier, the lead author of the study, from the Carnegie Institution for Science in America, said: “It’s as if you’re in a big, brightly-lit room, but you look around and see only a few 40-watt light bulbs. Where is all that light coming from?”

Intriguingly, the mismatch appears only in the nearby, relatively well-studied cosmos. When telescopes focus on galaxies billions of light-years away, everything adds up.