Half of the universe's hydrogen gas, long unaccounted for, has been found

Half of the universe's hydrogen gas, long unaccounted for, has been found

Astronomers tallying up all the normal matter—stars, galaxies and gas—in the universe today have come up embarrassingly short of the total matter produced in the Big Bang 13.6 billion years ago. In fact, more than half of normal matter—half of the 15% of the universe's matter that is not dark matter—cannot be accounted for in the glowing stars and gas we see.