Smoke is seen at the airport in Brussels, Belgium, after explosions were heard Tuesday. Police are reporting at least one person was killed and the terror level has been shifted to maximum level. Daniela Schwarzer/AP hide caption

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Daniela Schwarzer/AP

French fire brigade members aid an injured individual near the Bataclan concert hall following fatal shootings in Paris. Christian Hartman/Reuters/Landov hide caption

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Christian Hartman/Reuters/Landov

KABOOM! A NASA illustration of a gamma-ray burst. They occur, the space agency says, when "a massive star runs out of nuclear fuel, collapses under its own weight, and forms a black hole. The black hole then drives jets of particles that drill all the way through the collapsing star." NASA.gov hide caption

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NASA.gov

Fire fighters and utility workers at the scene of a massive gas explosion and fire Tuesday night in Kansas City, Mo. Orlin Wagner/AP hide caption

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Orlin Wagner/AP