Astronomers have long inferred that most of the material in the universe is invisible, existing as mysterious dark matter. But a recent study suggests that most ordinary matter is hidden as well.
Widely accepted studies of the cosmic microwave background—the afterglow of the Big Bang—indicate that for every pound of normal matter in the universe, there are about six pounds of dark matter, unseen particles that are known only from their gravitational pull. Because galaxies spring from dense clumps of both types of matter, researchers assumed that on average, the makeup of galaxies should exhibit a similar 1 to 6 ratio. “The parts should sum up to the whole,” says University of Maryland astronomer Stacy McGaugh. But when he examined more than 100 galaxies, he found that all had substantially less ordinary matter than predicted. The Milky Way showed just a quarter of the expected amount. Smaller galaxies yielded even ...
