"A signal of high-energy extraterrestrial neutrinos from unknown source(s) was recently discovered by the IceCube experiment."
Phys. Rev. D 98, 023004 (2018) - Multimessenger gamma-ray counterpart of the IceCube neutrino signal
https://journals.aps.org/prd/abstract/10.1103/PhysRevD.98.023004
Neutrinos can pass through ordinary matter where other parties cannot.
Take solar neutrinos for example. They come from the depths of a Star and offer us unprecedented info about thermonuclear reactions that occur the Solar core.
High-Energy Neutrinos, on the other hand, come from an unknown source produced by still unknown extraterrestrial objects. This information is not available by any other methods of observation.
Scientists from the National Research Nuclear University MEPhI, as well as colleagues from the Paris Diderot University (France), the Norwegian University of Science and Technology (Norway), the University of Geneva (Switzerland) have come across a new component in the gamma-ray flux as they peered into data obtained by the Fermi gamma telescope at high energies (above 300 GeV).
“At energies above 300 GeV, signals from sources outside our Galaxy will be severely suppressed by gamma-ray absorption in intergalactic space. At the same time, gamma radiation is practically not absorbed within the Galaxy. Thus, a source of the new component should be in our Galaxy”, explained Professor Dmitry Semikoz from MEPhI, and one of the authors of the new study.