Scientists working with the IceCube detector report a statistically significant signal of high-energy neutrinos coming from the plane of our Galaxy. Using 12 years of data and improved detector modelling, they find emission from the Galactic plane at a significance level the paper gives as 5.7σ, a commonly used threshold for a discovery in particle astrophysics. The excess is concentrated toward the inner part of the Milky Way.

The team combined three kinds of event selections that are sensitive to all three neutrino “flavours” (electron, muon and tau). One sample is dominated by “showers” (compact bursts of light produced when electrons, taus or neutral-current interactions deposit their energy). The other two samples include muon “tracks,” either starting inside the detector or passing through it. The full dataset contains about 1.07 million events, of which roughly 85,200 are classified as showers. The analysis compares the arrival directions and energies of events to predicted patterns on the sky from several models of Galactic neutrino production.

IceCube is a cubic-kilometre detector buried in Antarctic ice. It sees flashes of Cherenkov light made when charged particles travel faster than light does in ice. Track events make long light patterns and give good direction information. Shower events make compact light patterns and have worse direction but can add statistical power because they include more of the neutrino flavours. The main backgrounds are muons and neutrinos produced in Earth’s atmosphere. The analysis reduces those backgrounds by selecting events that start inside the instrumented volume and by using a likelihood method that mixes directional and energy information.

The reported excess is strongest in the shower sample. The paper highlights that the inner Galaxy shows 217 shower events with visible energy above 5 TeV, compared with a background expectation of 154.4 ± 4.1 events. Showers alone give a local significance of about 5.3σ, and the combined, all-flavour analysis reaches the stated global significance. The team tested several spatial templates that model how neutrino emission might follow gas and cosmic-ray distributions in the Galaxy. The best fit in their tests came from a template based on gamma-ray observations (the “Fermi-LAT π0” model).