Billions of galaxies dot the universe. We know they're made of stars and gas and other material. But we can't be sure whether the stars and gas in every galaxy are made of normal matter or antimatter -- matter with an opposite electric charge.
Astronomers are looking for evidence of antimatter in the observations of an experiment called BESS. Over the last decade and a half, giant balloons carried it high above most of Earth's atmosphere on flights lasting from a day to almost a month.
BESS has found particles of antimatter created when particles from exploding stars hit atoms out in space. But astronomers are hoping that its observations also contain evidence of atoms of antimatter.
Theory says that the Big Bang should have created equal amounts of matter and antimatter. But everything around us is made of normal matter. And that's a good thing, since matter and antimatter destroy each other in a burst of energy. Since we don't see this happening, it seems likely that the universe is made mostly of normal matter.
Even so, it's possible that pockets of antimatter are still around. In fact, entire galaxies could be made of antimatter, and they wouldn't look any different from those made of matter.
If there are antimatter galaxies, then some of their atoms should escape into space. BESS looked for these atoms during a flight last year. Scientists are still poring over the observations for signs of an antimatter universe.
Script by Damond Benningfield, Copyright 2009
For more skywatching tips, astronomy news, and much more, read StarDate magazine.