This is the fifth part of the Sources of Neutrinos series. We turn to a rare but extraordinary source: core-collapse supernovae — the deaths of massive stars that briefly outshine entire galaxies and release 99% of their energy as neutrinos.
What happens in a supernova
A star more massive than about 8 solar masses runs through nuclear fusion fuel in stages: hydrogen to helium, helium to carbon, carbon to neon, oxygen to silicon, silicon to iron. Iron is the end. Fusing iron costs energy rather than releasing it. When the star’s core has converted to iron, fusion stops supporting it against gravity.
The iron core — about 1.4 solar masses, the Chandrasekhar mass — collapses in less than a second. The collapse continues until the inner core reaches nuclear density. At that point the strong nuclear force halts further collapse, and the inner core rebounds. A shock wave propagates outward through the still-infalling outer core and envelope, eventually blowing the star apart.
The total gravitational binding energy released by the core collapse is roughly 3 × 10⁴⁶ joules — about 100 times the energy the Sun has produced in its entire 4.6-billion-year life, released in seconds. About 99% of this energy escapes as neutrinos. About 1% goes into kinetic energy of the explosion and even less (~0.01%) into electromagnetic radiation. The supernova we see as light is the small leftover after the neutrinos have already gone.
The neutrino signal
The neutrino emission from a supernova has three roughly distinguishable phases:
Neutronization burst (first ~10 ms after core bounce). Inverse beta decay $e^- + p \to n + \nu_e$ in the inner core converts protons to neutrons, producing a sharp burst of electron neutrinos. This is the signal that arrives first.
Accretion phase (next ~0.5 seconds). The shock wave stalls and matter accretes onto the proto-neutron star, producing copious thermal neutrino emission of all flavors.
Cooling phase (next ~10 seconds). The hot proto-neutron star cools by emitting roughly equal numbers of neutrinos of all six species ($\nu_e$, $\bar\nu_e$, $\nu_\mu$, $\bar\nu_\mu$, $\nu_\tau$, $\bar\nu_\tau$). About 99% of the supernova’s total neutrino emission happens in this cooling phase.
Total: roughly $10^{57}$ neutrinos released in ~10 seconds.
SN 1987A: the only one we’ve detected
On February 23, 1987, the blue supergiant Sanduleak −69° 202 in the Large Magellanic Cloud, 168,000 light-years from Earth, ran out of fuel and collapsed. Three operating neutrino detectors caught the burst:
- Kamiokande-II in Japan saw 11 events in 13 seconds.
- IMB in Ohio saw 8 events.
- Baksan in Russia saw 5 events.
Twenty-four total. From a supernova in a satellite galaxy. The detections occurred about 3 hours before optical telescopes saw the explosion — exactly as predicted, since the neutrinos escape the star instantly while the light takes hours to escape the expanding envelope.
The detection confirmed in 24 events what 50 years of theoretical work had predicted. It established neutrino astronomy as an observational discipline. Masatoshi Koshiba shared the 2002 Nobel Prize for his role at Kamiokande, with SN 1987A as a central piece of the citation.
Why we’ve only detected one
Galactic supernovae are rare. The expected rate is about one to three per century in the Milky Way. Most occur in regions obscured by dust, so they may not even be optically visible. SN 1987A is the only supernova close enough for neutrino detection in the modern era — and it was in a satellite galaxy.
The next galactic supernova will produce far more events:
- Super-Kamiokande would see roughly 8,000 events from a supernova at the Galactic center.
- DUNE’s 40-kiloton liquid argon mass would see roughly 3,000 events — disproportionately from $\nu_e$, complementary to water’s $\bar\nu_e$ sensitivity.
- IceCube would see a coincident rate spike of many thousands of events per second.
- JUNO, KM3NeT, and others would all see hundreds to thousands of events.
The combined network response would map the supernova’s neutrino emission across all flavors with unprecedented precision.
SNEWS: the early warning system
The Supernova Early Warning System (SNEWS) coordinates real-time alerts from all major operating neutrino detectors. When any detector sees what looks like a coincident burst, the system cross-correlates to confirm. A confirmed alert triggers automatic notifications to optical observatories worldwide, allowing them to point at the source location well before any visible light arrives.
The SNEWS system has been running since the early 2000s. It hasn’t triggered yet — we’re still waiting for the next supernova.
The Diffuse Supernova Neutrino Background
Even between rare galactic supernovae, the universe is full of antineutrinos from supernovae elsewhere. Roughly one core-collapse supernova per second explodes somewhere in the observable universe across cosmic history. The accumulated antineutrino flux at Earth — the Diffuse Supernova Neutrino Background (DSNB) — is about 10-20 electron antineutrinos per cm² per second.
That’s small but not zero. After decades of upgrades, current-generation detectors are now sensitive enough to detect it.
Super-Kamiokande loaded with gadolinium since 2020 should produce a first DSNB detection by 2026-2027. The Gd allows tagging the neutron from inverse beta decay, dramatically suppressing backgrounds.
The DSNB measurement would provide:
- Cosmic supernova rate — calibrating the integrated history of massive star deaths.
- Average neutrino spectrum — testing predictions of core-collapse simulations.
- Black hole formation rate — supernovae that collapse to black holes have different neutrino signatures.
What’s next
Beyond Super-K-Gd, future programs:
- Hyper-Kamiokande will multiply the DSNB statistics by ~5x once operating from 2027.
- DUNE will have unique sensitivity to the burst-neutronization phase of any future galactic supernova via $\nu_e + {}^{40}\text{Ar}$.
- The next galactic supernova — whenever it comes — will produce a single-event dataset of unprecedented scientific value.
The next part of this series turns to the highest-energy natural neutrinos: those produced in distant cosmic sources and in our own galaxy.
Frequently asked
How many neutrinos does a supernova produce?
A core-collapse supernova releases about 10⁵⁷ neutrinos of all flavors in roughly 10 seconds, carrying away about 99% of the explosion's total energy — about 3 × 10⁴⁶ joules. The light we see represents only about 1% of the actual energy released.
How many supernova neutrinos has humanity detected?
Twenty-four, all from SN 1987A in February 1987. Kamiokande-II in Japan saw 11, IMB in Ohio saw 8, and Baksan in Russia saw 5. No other supernova-neutrino burst has been detected since. The next galactic core-collapse supernova should produce thousands of events across modern detectors — the network is now ready.
What is the Diffuse Supernova Neutrino Background (DSNB)?
The DSNB is the integrated antineutrino glow from all core-collapse supernovae that have exploded in the observable universe — roughly one per second somewhere in the cosmos throughout cosmic history. The flux at Earth is about 10–20 electron antineutrinos per square centimeter per second. Super-Kamiokande-Gd is now sensitive enough to detect the DSNB and should produce a first measurement by 2026-2027.
When is the next supernova expected?
A core-collapse supernova in our Galaxy is expected roughly every 30-50 years, though the last visible one was in 1604 (Kepler's supernova). SN 1987A was in the Large Magellanic Cloud, a satellite galaxy. The next nearby galactic supernova could be tomorrow — or in another half century. Modern detectors are continuously ready, and the SNEWS alert system distributes the first hint of any neutrino burst worldwide within seconds.
Cite this article 5 formats
APA
Neutrino Times Editorial Team. (2026, February 27). Sources of Neutrinos — Part 5: Supernova neutrinos and the diffuse background. Neutrino Times. https://neutrino-times.com/articles/sources-of-neutrinos-part-5-supernova/
Chicago
Neutrino Times Editorial Team. "Sources of Neutrinos — Part 5: Supernova neutrinos and the diffuse background." Neutrino Times, February 27, 2026. https://neutrino-times.com/articles/sources-of-neutrinos-part-5-supernova/.
MLA
Neutrino Times Editorial Team. "Sources of Neutrinos — Part 5: Supernova neutrinos and the diffuse background." Neutrino Times, 27 Feb. 2026, https://neutrino-times.com/articles/sources-of-neutrinos-part-5-supernova/.
BibTeX
@misc{neutrino-times-sources-of-neutrinos-part-5-supernova,
author = {Neutrino Times Editorial Team},
title = {Sources of Neutrinos — Part 5: Supernova neutrinos and the diffuse background},
howpublished = {Neutrino Times},
year = {2026},
month = {feb},
url = {https://neutrino-times.com/articles/sources-of-neutrinos-part-5-supernova/},
note = {Accessed: 2026-02-27}
} RIS
TY - GEN TI - Sources of Neutrinos — Part 5: Supernova neutrinos and the diffuse background AU - Neutrino Times Editorial Team PY - 2026 DA - 2026-02-27 PB - Neutrino Times UR - https://neutrino-times.com/articles/sources-of-neutrinos-part-5-supernova/ ER -