An Image of the Milky Way Through a New Lens

A blue-tinted Milky War galaxy in a line against the blackness of space.
An artist’s composition of the Milky Way seen with a neutrino lens (blue). IceCube Collaboration/U.S. National Science Foundation (Lily Le & Shawn Johnson)/ESO (S. Brunier)

For the first time, the Milky Way Galaxy can be seen not through light, but through particles.

Researchers at The University of Alabama are part of an international group of over 350 scientists who produced an image of the Milky Way using neutrinos, tiny, ghostlike astronomical messengers, through the IceCube Neutrino Observatory buried deep in the ice of Antarctica. In a paper published in the journal Science, the researchers present evidence of high-energy neutrino emission from the Milky Way, the first time the project detected the particles in Earth’s home galaxy.

“IceCube had already uncovered evidence for astrophysical neutrino sources, but in both previous cases the objects involved were distant active galaxies. This is the first time we identify something closer to home, in this case, a seemingly diffuse glow of high-energy neutrinos from our own galaxy, the Milky Way,” said Dr. Marcos Santander, UA assistant professor of physics and astronomy.

Santander and Dr. Dawn Williams, professor of physics and astronomy, are both part of the IceCube Collaboration, a project supported by the National Science Foundation and 14 countries. Santander coordinates real-time searches for astrophysical neutrino sources, and Williams plays a key role in calibration and characterization efforts to expand the IceCube telescope.

A metal, scientific building with silo sits on the ice and snow with the Milky Way visible in the night sky.
The IceCube Lab is seen under a starry, night sky, with the Milky Way appearing over low auroras in the background. Yuya Makino, IceCube/NSF

The IceCube Neutrino Observatory is an array of over 5,000 basketball-sized optical sensors deeply encased within a cubic kilometer of clear Antarctic ice. The observatory was set up to detect neutrinos, abundant subatomic particles famous for passing through anything and everything, rarely interacting with matter. About 100 trillion neutrinos pass through our bodies every second.

Having identified sources of neutrino emission in other galaxies, the project continued to search for sources in the Milky Way. 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.

The neutrinos from the Milky Way were spotted, so to speak, through the development and application of advanced machine learning tools by IceCube researchers from Drexel University and TU Dortmund University in Germany that identified potential astrophysical neutrinos in existing data and reconstructed their incoming direction in the sky to map their origin.

“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,” says Dr. Francis Halzen, a professor of physics at the University of Wisconsin–Madison and principal investigator of IceCube.