IceCube detects high-energy neutrino emission from the galactic plane of the Milky Way | Ski.News

Observations of high-energy astrophysical neutrinos have shown that they mainly come from extragalactic sources such as active galaxies. However, gamma-ray observations show light emission from within our galaxy, the Milky Way, and gamma-rays and astrophysical neutrinos are expected to be produced by the same physical processes. The IceCube Neutrino Observatory – a cubic kilometer particle detector built deep in Antarctic ice – looked for neutrino emission from within the Milky Way and found evidence of extra neutrinos being 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 from nearby sources within the Milky Way.

An artist composition of the Milky Way seen through a neutrino lens (blue).  Image credit: IceCube / NSF / Lily Le / Shawn Johnson / ESO / S. Brunier.

An artist composition of the Milky Way seen through a neutrino lens (blue). Image credit: IceCube / NSF / Lily Le / Shawn Johnson / ESO / S. Brunier.

What is intriguing is that, unlike the case of light of any wavelength, in neutrinos, the Universe eclipses nearby sources in our galaxy, said Professor Francis Halzen of the University of Wisconsin-Madisons, 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, confirming what we know about our Galaxy and cosmic ray sources, said Steve Sclafani, IceCube member, Ph.D. student at Drexel University.

The search focused on the southern sky, where most neutrino emission is expected from the galactic plane near the center of the Milky Way.

However, until now, the background of muons and neutrinos produced by cosmic ray interactions with the Earth’s atmosphere has posed significant challenges.

To overcome them, the IceCube team developed analyzes that screen for cascading events or neutrino interactions in ice that result in roughly spherical showers of light.

Since the energy deposited by the cascade events begins within the instrumented volume, contamination by atmospheric muons and neutrinos is reduced.

Ultimately, the higher purity of the cascade events gave better sensitivity to astrophysical neutrinos from the southern sky.

However, the final breakthrough has come from the implementation of machine learning methods that improve the identification of neutrino cascades, as well as their direction and energy reconstruction.

The observation of neutrinos from the Milky Way is a hallmark of the critical emergent value that machine learning provides in data analysis and event reconstruction in the IceCube.

The improved methods have allowed us to retain over an order of magnitude more neutrino events with improved angular reconstruction, resulting in an analysis that is three times more sensitive than previous research, said IceCube member Mirco Hnnefeld, Ph. D. student at TU Dortmund.

The dataset included 60,000 neutrinos spanning 10 years of IceCube data, 30 times more events than the selection used in a previous analysis of the galactic plane using cascading events.

These neutrinos were compared to previously published prediction maps of places in the sky where the Galaxy was expected to glow with neutrinos.

The maps included one extrapolated from Fermi Large Area Telescope gamma-ray observations of the Milky Way and two alternative maps identified as KRA-gamma by the group of theorists who produced them.

This long-awaited detection of cosmic ray interactions in the Galaxy is also a wonderful example of what can be achieved when modern methods of knowledge discovery in machine learning are applied consistently, said Professor Wolfgang Rhode of TU Dortmund University , member of the IceCube Collaboration.

The power of machine learning offers great future potential, bringing other observations closer to hand.

The strong evidence that the Milky Way is a source of high-energy neutrinos survived the collaboration’s rigorous tests, said Professor Ignacio Taboada of the Georgia Institute of Technologys, a spokesperson for the IceCube collaboration.

Now the next step is to identify specific sources within the Galaxy.

These and other questions will be addressed in IceCube’s planned follow-up analyses.

Observing our Galaxy for the first time using particles instead of light is a huge step forward, said Professor Naoko Kurahashi Neilson of Drexel University, a member of the IceCube Collaboration.

As neutrino astronomy evolves, we will have a new lens with which to observe the Universe.

The results were published in the journal Science.

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IceCube collaboration. 2023. Observation of high-energy neutrinos from the galactic plane. Science 380 (6652): 1338-1343; doi: 10.1126/science.adc9818

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