Like the spin of a cosmic coin, a unique set of particle oscillations could ultimately decide the fate of the Universe’s biggest suns.
Simulations by a team led by physicists from Waseda University in Tokyo suggest the quantum flip-flopping of tiny particles known as neutrinos makes a critical difference in whether a massive star ends in a spectacular explosion or quietly collapses into oblivion.
While the researchers acknowledge their modeling could benefit from some fine-tuning, their findings suggest that current descriptions of core-collapse supernovae may be incomplete unless they take into account subtle changes in neutrino properties.
Neutrinos aren’t referred to "ghost particles" for nothing. With near-zero masses and no electromagnetic charge, they barely interact with other particles, despite flooding space in vast numbers.
It’s understood that they come in three forms called flavors, each associated with the electron, muon, and tau elementary particle. For more than half a century, it’s been clear that the quantum nature of individual neutrinos oscillates between these flavors as they move.
Deep inside the dense confines of a dying star, swarms of neutrinos swap flavors with split-second tiny over distances measured in fractions of an inch. These "fast flavor conversions" aren’t easily dismissed under the extreme conditions of a stellar core, yet according to the researchers, previous simulations have delivered contradictory results.
In a new attempt to understand the neutrino’s dynamics, the scientists implemented a model that hadn’t been applied before. Known as a subgrid, it allowed them to represent processes that couldn’t be refined computationally.
Using this new approach, the team showed how fast flavor conversions inside a massive star’s packed core lead to one of two outcomes – a core-collapse supernova, or a failed explosion.
Core-collapse supernovae are among the Universe’s most violent events, emitting as much energy as our Sun will in its entire lifespan in a few short seconds. The recoil of the collapsing core casts heavy elements far through surrounding space, leaving behind a dense ball of matter known as a neutron star.
At the other extreme, a core can forgo the energetic bounce and fall forever into itself as a black hole, shrugging off its layers of hot gas quietly and silently.
Which event unfolds depends on the thermodynamics of the core, or "proto-neutron star". This, in turn, depends on the precise interactions of neutrino flavors as they pass through the crowd of atomic nuclei.
The researchers discovered that the rate at which matter is squeezed into the core makes all the difference. A slower accretion of material allows fast flavor conversion to deliver enough heat to drive a supernova. A rapid pile-up is more likely to lead to a failed explosion.
As neutrino observatories like the ICE experiment in Antarctica continue to collect data on neutrinos streaming down from above and up through our planet, we may learn more about the role some of physics’ smallest particles play in astronomy’s most powerful phenomena.
This research was published in Physical Review Letters.
Fact-checked by Bronwyn Thompson
