Researchers at the University of Copenhagen have developed the most detailed model so far of neutrinos produced by stars across the Milky Way and of how many of these particles reach Earth. The model provides a galaxy-wide estimate of the neutrino flux from stellar nuclear reactions and traces where in the galactic disk these particles originate. The work has been published in Physical Review D.

"For the first time, we have a concrete estimate of how many of these particles reach Earth, where in the galaxy they come from, and how their energy is distributed. Because ghost particles come straight from the core of stars, they can tell us things that light and other radiation cannot," says lead author of the new study, postdoc Pablo Martinez-Mirave from the Niels Bohr Institute.

To construct the map, the team combined advanced stellar models with positional and population data from ESA's Gaia space telescope to identify where in the Milky Way neutrinos mainly originate. This approach allowed them to calculate the neutrino production of stars of different masses and ages and then integrate these contributions over the full stellar population of the galaxy.

The study shows that most stellar neutrinos that reach Earth come from the crowded region around the galactic center, where the density of stars is highest, with especially strong contributions from regions a few thousand light-years from our planet. Stars with masses comparable to or higher than the Sun dominate the emission, and this directional dependence means detectors will see the strongest signal when they observe toward the center of the galaxy.

This new mapping offers a practical tool for experiments that aim to detect galactic neutrinos using large detectors placed deep underground or under ice or water. With the flux distribution now quantified, observatories can refine their observing strategies and improve the chances of separating a Milky Way neutrino signal from other background sources. "Now we know more precisely where to look for Galactic neutrinos. Our results show that most neutrinos are produced in stars that are as massive or more massive than the Sun. This means that the best chance of detecting neutrino signals is when looking towards the galactic centre, where the signal is the strongest," explains Pablo Martinez-Mirave.

The mapping also clarifies how neutrino emission depends on stellar properties. The results indicate that younger, more massive stars generate the highest neutrino output, while lower-mass and older stars contribute at lower levels across a wide energy spectrum. Most of the particles arise from nuclear reactions in stellar cores, with an additional contribution from thermal processes inside stars.

Unlike light, X-rays, or gamma rays, neutrinos can travel enormous distances almost unaffected by intervening matter and fields, preserving information about the environments in which they were created. For decades, measurements of solar neutrinos have provided insight into conditions deep inside the Sun, and the researchers suggest that a similar approach, extended to the entire stellar population of the galaxy, could eventually reveal details of stellar life cycles and galactic structure that are not accessible through electromagnetic observations alone.

"Neutrinos carry information straight from the interior of stars. If we learn to harness them, they can give us new insights into stellar life cycles and the structure of our galaxy in a way no other source can," says senior author of the study, Professor Irene Tamborra from the Niels Bohr Institute. Because neutrinos are expected to propagate over galactic distances with only minimal alteration, they also offer a sensitive way to test the limits of known physics.

The researchers point out that even small discrepancies between observed neutrino behavior and standard model predictions could indicate new physical phenomena. "Because neutrinos are barely affected, we have clear expectations of how they should behave on their long journey to Earth. So even tiny deviations in their behaviour would be a strong clue to new, unknown physics," says Irene Tamborra. "With neutrinos, it's like dimming the lights in a room and suddenly seeing what was hidden in the dark - and with this new model, we now have both a map and a compass to start navigating it."

According to the team, the model provides a baseline for interpreting future signals from current and next-generation neutrino observatories. As detectors improve in sensitivity and directional capability, the map of stellar neutrinos from the Milky Way could help separate different neutrino populations, such as those from the Sun, distant supernovae, or other high-energy cosmic events, and refine understanding of how stars throughout the galaxy contribute to the overall neutrino background at Earth.

Research Report:Neutrinos from stars in the Milky Way

Related Links
University of Copenhagen
Stellar Chemistry, The Universe And All Within It