In September 2017, IceCube detected a high-energy neutrino whose direction pointed back to a blazar called TXS 0506+056, a galaxy billions of light years away with a jet aimed directly at Earth. Gamma-ray observatories recorded a simultaneous brightening from the same source, and this coincident detection of neutrinos and gamma rays gave the first real evidence that such extragalactic jets can act as cosmic particle accelerators.
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Neutrinos have near-zero mass and travel at close to light speed, so they can sometimes reach Earth before light from the same event because light gets delayed interacting with surrounding matter.
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Before this detection, IceCube could estimate neutrino energies fairly well but had more trouble pinning down direction for certain event types.
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52:46We had a good estimate maybe of the energies, but maybe not like the direction because of those two types of events that I was telling you about. But certain events, we could actually pinpoint. And in September, 2017, IceCube detected a high energy neutrino with a direction that was consistent with a blazar. The blazar is called TXS-0506 plus 056. This is at the edge of our universe. It's extremely tiny. This is not anywhere near us, okay? Billions of light years away. A blazar is an active galaxy with a jet that's directed towards us. And you can imagine the galaxy's jet is looking straight at us, which is why it's so bright for
53:30how far away it is. The galaxy also brightened in gamma rays. We have gamma ray observatories that had coincident detection. We like coincident detection. We like coincident detection because that means something happened in this blazar, right? There was some event that released a bunch of gamma rays and a bunch of neutrinos. Neutrinos, because they're so light, they're like near zero mass, they travel at about the same speed as light. Sometimes they even arrive before light because the light interacts with a bunch of stuff and gets delayed and then comes to us. The neutrinos just on its way from whatever event. And so in 2017, we got kind of an indication that actually it could be, in fact, these extra
54:14galactic jets.