Observations of high-energy astrophysical neutrinos have shown that they mostly originate from extragalactic sources such as active galaxies. However, gamma ray observations show bright emission from within our Milky Way Galaxy, and astrophysical gamma rays and neutrinos are expected to be produced by the same physical processes. The IceCube Neutrino Observatory — a cubic-kilometer particle detector built deep within Antarctic ice — searched for neutrino emission from within the Milky Way and found evidence of extra neutrinos emitted along the Galactic plane, which is consistent with the distribution of gamma-ray emission. The results imply that high-energy neutrinos can be generated by nearby sources within the Milky Way.
“What’s intriguing is that, unlike the case for light of any wavelength, in neutrinos, the Universe outshines the nearby sources in our own Galaxy,” said University of Wisconsin-Madison’s Professor Francis Halzen, principal investigator of the IceCube Collaboration.
Interactions between cosmic rays — high-energy protons and heavier nuclei, also produced in our Galaxy — and galactic gas and dust inevitably produce both gamma rays and neutrinos.
Given the observation of gamma rays from the Galactic plane, the Milky Way was expected to be a source of high-energy neutrinos.
“A neutrino counterpart has now been measured, thus confirming what we know about our Galaxy and cosmic ray sources,” said IceCube member Steve Sclafani, a Ph.D. student at Drexel University.
The search focused on the southern sky, where the bulk of neutrino emission from the Galactic plane is expected near the Milky Way’s center.
However, until now, the background of muons and neutrinos produced by cosmic-ray interactions with the Earth’s atmosphere posed significant challenges.
To overcome them, the IceCube team developed analyses that select for cascade events, or neutrino interactions in the ice that result in roughly spherical showers of…
Read the full article here