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Summary
If astronomers are right, a ghostly particle that lit up an instrumented swath of ice beneath the south pole on 22 September 2017 was a messenger from a distant galaxy. The particle was a neutrino, electrically neutral and almost massless, whose path could be traced directly back to the violent cosmic events that created it. Cued by IceCube, the Antarctic detector, an orbiting telescope found that the neutrino likely came from a distant blazar, a bright source of radiation powered by a supermassive black hole. The new finding could mark the founding event of so-called neutrino astronomy and also triggered a powerful example of another new trend, multimessenger astronomy, in which telescopes studied the flaring blazar across electromagnetic spectrum, from gamma rays to radio waves. And if the result holds up, the neutrino-producing blazar could also help solve a decades-old mystery in astronomy: Where do the extremely high energy protons and other nuclei that occasionally bombard Earth come from?
