Gamma-Ray Sky
 This view of the universe shows the brightest sources of gamma rays, which are the most energetic form of radiation in the universe. Most of the activity is clustered along the plane of our home galaxy, the Milky Way (red band across the center). Individual objects include the Crab Nebula and a star system known as Geminga (far right edge), and a galaxy about 233 million light-years away known as NGC 1275 (at left, below the band of the Milky Way). Gamma rays are produced by some of the most powerful objects in the universe, including exploding stars and superhot disks of gas around black holes. This image was compiled by the space-based Fermi telescope. [NASA/DOE/Fermi]
These powerful events announce themselves to the universe with the most powerful form of energy, known as gamma rays. They contain millions of times as much energy as visible light, but they're invisible to human eyes. And even if we could see them, it wouldn't matter, because Earth's atmosphere prevents them from reaching the surface.
The only way to see gamma rays directly is to loft telescopes above the atmosphere with balloons or rockets. But we can see them indirectly with special detectors on the ground.
Gamma rays tell us about some of the most fascinating objects in the universe. That includes the objects known as gamma-ray bursts -- the most powerful outbursts in the entire universe. They may be created when a giant star blasts itself to bits -- perhaps giving birth to a black hole in the process. Such an outburst produces more energy in a few seconds than the Sun will produce in its entire lifetime.
Gamma rays also come from the disks of gas around black holes. The gas is accelerated to near lightspeed by the black hole's gravity, so it emits enormous amounts of energy.
And it's even possible that gamma rays could come from the mysterious stuff known as dark matter -- and we'll talk about that tomorrow.
Script by Damond Benningfield, Copyright 2009
For more information, visit StarDate's Black Holes Encyclopedia.
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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