IceCube had already definitively detected neutrinos streaming in from outside the Milky Way, but it couldn’t be said with certainty that any of them came from within the galaxy, says Francis Halzen, lead investigator of the project and a physicist at the University of Wisconsin–Madison. This was rather strange, considering the proximity of the Milky Way’s disk (in fact, our solar system is embedded in it) and the high likelihood that neutrinos form there.