Most of the universe is dark. Not just the empty spaces between stars and galaxies, but the stuff that makes up the universe itself. In fact, about a quarter of everything in the universe may consist of dark matter. It produces no detectable energy, but its gravity pulls on the "normal" matter around it.
While individual particles of dark matter are dark, if you get two of them together they may get quite bright. Some theories suggest that a collision between dark-matter particles may produce gamma rays -- the most powerful form of energy.
Earth's atmosphere blocks the gamma rays, so they don't reach the surface. Instead, they strike molecules high in the sky, creating showers of particles and energy. Special telescopes look for these flashes of energy.
One telescope is in Arizona, while another is in Namibia. Each one consists of four separate dishes that look like large radio dishes. But they have honeycomb-like arrays of mirrors to gather light. Each set of dishes works together to form a single telescope.
The telescopes have looked for signs of dark matter in a gamma-ray glow that fills the center of the Milky Way galaxy, as well as the centers of several neighboring galaxies. Astronomers know how much gamma-ray energy comes from other sources, so they look for the dark matter collisions as extra gamma rays, of a certain energy level. So far, they've come up empty. But the search continues.
More about gamma-ray astronomy tomorrow.
Script by Damond Benningfield, Copyright 2009
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