An exploding star could send highly energetic neutrinos toward Earth several days before reaching its maximum brightness.
Before some supernovas, the dying star loses a great deal of matter. This gas remains around it and forms a dense envelope. When the star’s core collapses, the explosion launches a shock wave that travels through this accumulated matter. This is the region where the authors studied neutrino production.
Artist’s impression of matter and dust forming around a supernova explosion.
Credit: ESO/M. Kornmesser, CC BY 4.0.
Neutrinos are particles that barely interact with matter. They can pass through an entire planet without being stopped. This property makes them difficult to detect, but it also allows them to carry information directly from regions that light struggles to escape.
In the model calculated by the researchers, the shock eventually accelerates protons to very high energies. Their collisions with the surrounding matter then produce secondary particles, including neutrinos. These can reach energies between 1 and 100 teraelectronvolts, far beyond those usually observed.
The timing of their emission is particularly interesting. A significant portion of the energy carried by neutrinos would be released very quickly at the moment of the explosion. This signal could arrive before the supernova’s visible light peak. Telescopes would therefore not yet observe the star at its maximum brightness.
The highly energetic gamma rays produced in the same place do not necessarily escape as easily as neutrinos.
The authors calculated that these explosions could contribute to the high-energy neutrino background observed in the sky. However, this possibility depends on an important assumption: the mass loss preceding the explosion must be sufficiently substantial in massive stars.
In practice, individual detections would remain rare. The researchers estimate that a detector covering about 1 km² could record more than one neutrino from such a supernova approximately once every twenty years. An installation ten times larger could reach about one event per year.