Scientists have presented the first strong evidence for the emission of neutrinos in our galaxy, which are called ghost particles because they exist in large quantities but are not detected. The neutrino-based image of our galaxy is the first of its kind and is presented in a publication in the journal Science.

The discovery was achieved through a collaboration of more than 350 researchers, who used the IceCube Neutrino Observatory located in Antarctica and supported by the US National Science Foundation. The Observatory detects the signatures of high-energy neutrinos in space using thousands of interconnected sensors, buried deep within a cubic kilometer of ice.

Not only was the challenge for the researchers to detect the notoriously elusive neutrinos and distinguish them from other types of interstellar particles, but also the ambitious goal of determining their origin. When neutrinos happen to interact with the ice beneath the IceCube Observatory, these rare encounters produce faint patterns of light, which the Observatory can detect.

Certain patterns of light clearly point to a specific region of the sky, allowing researchers to pinpoint the source of the neutrinos. Such interactions formed the basis for the discovery, in 2022, of neutrinos coming from another galaxy 47 million light-years away.

Other interactions produce stormy “balls of light” in the clear ice, and the researchers developed a machine learning algorithm to compare the relative position, size and energy of more than 60,000 such neutrino-generated light bursts recorded by IceCube over ten years.

The researchers spent more than two years testing and verifying their algorithm, using artificial data simulating neutrino detections. When they finally fed the algorithm with the actual data provided by IceCube, an image emerged that showed bright spots, which corresponded to places in our galaxy that were thought to be emitting neutrinos. These sites were located where the observed γ-rays were thought to be byproducts of collisions between cosmic rays and interstellar gas and should theoretically also produce neutrinos.

“As is so often the case, major breakthroughs in science are made possible by advances in technology,” said Denise Caldwell, director of the US National Science Foundation’s Physics Department.

“The capabilities provided by the highly sensitive IceCube probe combined with new data analysis tools have given us a completely new view of our galaxy, one that had only been hinted at before. As these capabilities continue to improve, we can look forward to watching this picture emerge with ever greater resolution, potentially revealing hidden features of our galaxy that humanity has never seen before,” she adds.