The Universe’s Most Elusive Particles Might Be Talking to Themselves

Collapsing stars might act as cosmic laboratories for discovering hidden neutrino interactions.

Neutrinos are among the most puzzling particles in the universe. Nearly massless and incredibly elusive, they rarely interact with anything, yet they play a deadly role in the life cycle of stars far larger than our sun. These subatomic particles exist in three known types—electron, muon, and tau—and despite decades of study, many of their behaviors remain poorly understood.

Because neutrinos interact so weakly, it is nearly impossible to make them collide under laboratory conditions. As a result, scientists still do not know whether they follow the interaction rules laid out by the standard model of particle physics or if they engage in theorized “secret” interactions exclusive to neutrinos.

In a new study, researchers with the Network for Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS), including members from UC San Diego, have used theoretical models to demonstrate that massive stars in the final stages of their lives may naturally provide the perfect setting for studying these interactions.

As these stars collapse, neutrinos carry away thermal energy, which leads to the stars contracting further. This contraction accelerates the electrons inside to nearly the speed of light, pushing the stars toward instability and eventual collapse.

The Role of Neutrino Interactions in Stellar Collapse

Eventually, the collapsing star’s density becomes so high that the neutrinos are trapped and collide with each other. With purely standard model interactions, the neutrinos will be mostly electron flavor, the matter will be relatively “cold,” and the collapse will likely leave a neutron star remnant. However, secret interactions that change neutrino flavor radically alter this scenario, producing neutrinos of all flavors and leading to a mostly neutron “hot” core that may lead to a black hole remnant.

Fermi National Accelerator Lab’s upcoming Deep Underground Neutrino Experiment (DUNE) might be able to test these ideas, as might future observations of the neutrinos or gravitational waves from collapsing stars.

Reference: “Nonconservation of Lepton Numbers in the Neutrino Sector Could Change the Prospects for Core Collapse Supernova Explosions” by Anna M. Suliga, Patrick Chi-Kit Cheong, Julien Froustey, George M. Fuller, Lukáš Gráf, Kyle Kehrer, Oliver Scholer and Shashank Shalgar, 18 June 2025, Physical Review Letters.
DOI: 10.1103/gnp5-4y8k

Their research was funded, in part, by the National Science Foundation (PHY-2209578 and PHY-2020275), the Department of Energy (DE-AC02-07CHI11359), and the Heising-Simons Foundation (2017-228).

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