What's Hot This Week Universe's Most Powerful Explosions Can Leave Black Hole Graves By Clara Moskowitz When certain stars collapse, they release overwhelming blasts of energy called gamma-ray bursts - the most powerful explosion in the universe. But the cosmic leftovers of these violent outbursts have been a mystery Ñ until now.     Should Pluto Be a Planet After All? Experts Weigh In By Mike Wall Now that Pluto may have regained its status as the largest object in the outer solar system, should astronomers consider giving it back another former title - that of full-fledged planet?     Sponsored by: Earth at Night: Astronaut Shares Dazzling Photos From Space Station Secret U.S. Spy Satellite Launches Into Orbit on Huge Rocket Tiny Asteroid That Buzzed Earth Is a Fast-Spinning Rock Eminent Astronomers Brian Marsden, 73, and Allan Sandage, 84, Die From Illnesses Rocket Loaded With Solar Sail and Satellites Blasts Off From Alaska

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