Science: Nature's Own H-Bombs

Puzzling bursts of energy in space may be thermonuclear blasts

Since 1963, the Pentagon's Vela satellites have been vigilantly circling the earth, using their electronic sensors to detect radiation from surreptitious nuclear explosions outside the U.S. Though these orbital watchdogs have identified only a few suspicious events, they have accidentally uncovered a major astronomical mystery: violent outbursts of energy, in the form of X rays and gamma rays, that are observable only above the earth's atmospheric shield. Such puzzling "highenergy transients," as scientists call them, rarely last more than ten seconds, yet...

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