The Crab Nebula is the result of a supernova observed by Chinese astronomers in 1064, making it one of the more recent remnants available to study. Its core contains a rapidly spinning pulsar, which helps power a shockwave that produces emissions that run from the infrared, across the visible, and into the gamma-ray portion of the spectrum. In general, its output has been so consistent that astronomers have actually used it to calibrate orbiting observatories. But over the last few years, several of these observatories have picked up sudden surges in the nebula's output that hint at electrons traveling with energies of a Peta-electron Volt.
These outbursts don't come along that often—there seem to have only been three of them since 2007—and they last for just a handful of days. But we've now got a set of telescopes capable of picking up these events, and two of them, Fermi and AGILE, each caught two of the three (one occurred before Fermi was in orbit; AGILE was pointing in a different direction during another).
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Cindy Crawford Mariah OBrien Uma Thurman Alice Dodd Kate Walsh
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