If you have ever wondered where the trillions of neutrinos passing through your body every second actually come from, the honest answer is: lots of places. Some are nearby and obvious; some are billions of light-years away and only barely detectable. Together they form one of the most informative cosmic accounting problems in physics. This article walks through every major neutrino source, what makes each one distinct, and how detectors tell them apart.
The single rule that organises the whole list is straightforward: a neutrino is produced wherever a weak-interaction process happens. Anywhere protons turn into neutrons, anywhere neutrons decay, anywhere a pion or muon decays in flight — there is a neutrino in the products. Once you know that, the catalogue almost writes itself.
The Sun: by far the dominant source
The Sun’s core is a nuclear fusion reactor running on the proton–proton chain and, at higher temperatures, the CNO cycle. Every time four protons fuse into a helium-4 nucleus, the chain releases two electron neutrinos. The Sun’s total power, scaled by the energy per fusion, gives a neutrino emission rate of roughly 2 × 10³⁸ per second, in every direction.
By the time those neutrinos reach Earth at 1 astronomical unit, the flux is about 65 billion per square centimetre per second. That is the number physicists have measured by sending solar neutrinos through tens of thousands of tons of cleaning fluid, heavy water, ice, and liquid scintillator — at experiments from Homestake to SNO, Super-Kamiokande, Borexino, and now JUNO. The flux is so dominant that essentially all of the 100 trillion neutrinos passing through your body every second are solar.
The full detail sits in our solar neutrinos explainer. Solar neutrinos were also the first source to demonstrate that neutrinos oscillate between flavours.
Cosmic rays in the upper atmosphere
When high-energy cosmic rays hit the upper layers of Earth’s atmosphere, they produce showers of pions and muons. Pions decay into muons and muon neutrinos; muons decay into electrons, electron neutrinos, and more muon neutrinos. The result is a continuous downpour of atmospheric neutrinos at energies from hundreds of megaelectronvolts up into the teraelectronvolt range.
The flux is much smaller than the solar flux — of the order of one neutrino per square centimetre per second — but the energies are far higher, and the direction-dependent pattern (neutrinos arriving from below have travelled through the Earth, those from above have only travelled a few tens of kilometres) was the smoking-gun signature for oscillation discovered by Super-Kamiokande in 1998.
See our atmospheric neutrino flux explainer and our atmospheric sources article.
Nuclear reactors
Every commercial nuclear reactor in the world is an intense source of electron antineutrinos. Fission products are neutron-rich and beta-decay back toward stability, and every beta decay produces an antineutrino. A typical large reactor emits about 2 × 10²⁰ antineutrinos per second.
Reactor antineutrinos were used by Cowan and Reines to make the first-ever detection of a neutrino in 1956. Modern reactor experiments — Daya Bay, RENO, Double Chooz, KamLAND, and now JUNO — exploit them for some of the most precise measurements in neutrino oscillation physics. The same physics is the basis of compact reactor-monitoring concepts developed for nuclear non-proliferation work. See our reactor sources explainer.
Particle accelerators
Accelerators are the other major human-made neutrino source. Pulsed proton beams hit a target, producing pions and kaons; the secondaries decay in flight in a long tunnel, producing collimated neutrino beams that can be aimed at long-baseline detectors hundreds of kilometres away.
T2K fires its beam from J-PARC in Tokai through 295 km of Earth to Super-Kamiokande in Kamioka. NOvA fires from Fermilab in Illinois 810 km to Ash River in Minnesota. The upcoming DUNE will fire from Fermilab 1,300 km to the Sanford Underground Research Facility in South Dakota. The European LBNF, Hyper-K’s beam from J-PARC, and various short-baseline beams round out the global accelerator-neutrino programme.
Accelerator beams are the cleanest way to study CP violation in oscillations, because the beam’s flavour composition and energy spectrum are tightly controlled. See our accelerator sources explainer.
Supernovae
Core-collapse supernovae release about 99 per cent of their gravitational binding energy as neutrinos in a few seconds. The number is staggering: the typical core-collapse event emits ~10⁵⁸ neutrinos, more in that brief moment than the entire universe emits in light in the same interval.
The 1987 supernova SN 1987A in the Large Magellanic Cloud produced a clearly detected burst of about 24 neutrinos across three observatories, three hours before the optical flash. That single event proved that neutrino astronomy was possible and constrained both core-collapse physics and neutrino properties. The next galactic supernova will deliver a dataset orders of magnitude richer thanks to today’s detectors — Super-Kamiokande, IceCube, JUNO, and eventually Hyper-Kamiokande. See our supernova sources explainer and the SN 1987A retrospective.
The cumulative emission from all supernovae across cosmic history forms the diffuse supernova neutrino background, currently being searched for at very low rates by Super-K and JUNO.
Cosmic accelerators: blazars, AGN, and the galactic plane
At the highest energies — teraelectronvolts to petaelectronvolts — neutrinos are produced when extragalactic accelerators (active galactic nuclei, blazars, possibly tidal disruption events) accelerate protons that then collide with surrounding matter or radiation. IceCube has been catching these cosmic neutrinos at a rate of about one per month at very high energies for over a decade.
The 2017 alert tying a single neutrino to the flaring blazar TXS 0506+056 launched routine multi-messenger neutrino astronomy. The 2022 identification of NGC 1068 as a steady neutrino source and the 2023 detection of the Milky Way’s own galactic plane as a diffuse emitter followed. See our cosmic sources explainer.
The radioactive Earth
The interior of the Earth is full of slowly decaying uranium, thorium, and potassium left over from the planet’s formation. Their beta decays produce geo-neutrinos — antineutrinos at a much lower flux than reactor or solar, but with their own distinctive spectrum. Catching them gives a direct measurement of the radioactive heat budget driving plate tectonics. See our geo-neutrinos explainer.
The Big Bang
The very oldest neutrinos in the universe are relics from a fraction of a second after the Big Bang. As the universe cooled, neutrinos decoupled from the rest of the plasma and have been streaming ever since at very low energies (a few ten-thousandths of an electronvolt today). Their density is about 336 per cubic centimetre, everywhere — more than all the other sources combined by number, though so low in energy that none has ever been directly detected.
They influence cosmology through their effect on structure formation and the cosmic microwave background, and are an active target of next-generation cosmology experiments. See our cosmological neutrino background explainer.
How detectors tell them apart
The catalogue above is a list of sources, not a list of event types. A given detector sees neutrinos from many of these sources simultaneously, and the analysis job is to disentangle them.
Three features do most of the work: energy (solar neutrinos are MeV, cosmic are TeV–PeV), direction (solar arrive from the Sun, atmospheric from all sky, cosmic from specific directions), and time (a supernova burst arrives in seconds; reactor antineutrinos correlate with reactor operations). Combining all three lets detectors assign each event to a likely source category, even when the underlying interaction looks similar.
The takeaway
Neutrinos come from anywhere in the universe where the weak nuclear force is at work — the Sun, the atmosphere, reactors, accelerators, supernovae, distant accelerating galaxies, the radioactive Earth, and the early universe itself. Their dominance by source depends on what you measure: by flux, the Sun wins; by number density, the cosmic background wins; by single-event impact, a galactic supernova wins.
For more, see the complete neutrino primer, what a neutrino is, and the six-part sources series.
Related reading: How many neutrinos pass through your body?, SN 1987A: the supernova that opened neutrino astronomy, Geo-neutrinos: listening to the Earth’s radioactive heart.
Frequently asked
What is the most common source of neutrinos on Earth?
The Sun, by a very large margin. Solar fusion produces roughly 65 billion neutrinos per square centimetre per second at Earth — about 100 trillion crossing every human body each second. All other sources combined deliver a tiny fraction of that flux.
Do nuclear reactors produce neutrinos?
Yes — large numbers. Nuclear fission in reactor cores produces about 2 × 10^20 antineutrinos per second per typical commercial reactor. They are how experiments like KamLAND, Daya Bay, and JUNO study neutrino oscillation, and they are the basis of new reactor-monitoring proposals for non-proliferation work.
Where else in the universe do neutrinos come from?
Cosmic ray showers in Earth's upper atmosphere produce 'atmospheric' neutrinos; core-collapse supernovae release about 99% of their energy as neutrinos; active galactic nuclei accelerate particles that emit cosmic neutrinos detected by IceCube; the radioactive interior of the Earth produces 'geo-neutrinos'; and a relic background of cosmological neutrinos fills all of space at 336 per cubic centimetre, left over from the Big Bang.
Can humans make neutrinos in a lab?
Yes. Particle accelerators produce focused 'accelerator neutrino beams' aimed at long-baseline detectors hundreds of kilometres away — for example T2K from J-PARC into Super-Kamiokande, NOvA from Fermilab to northern Minnesota, and the upcoming DUNE beam from Fermilab to South Dakota. Nuclear reactors are likewise human-made antineutrino sources.
How do you tell different sources of neutrinos apart?
By their energy spectrum and arrival direction. Solar neutrinos have energies up to a few megaelectronvolts and arrive from the Sun; atmospheric neutrinos have a broad spectrum and arrive from all directions; reactor antineutrinos have a characteristic few-MeV spectrum; cosmic neutrinos reach teraelectronvolt to petaelectronvolt energies. Detectors combine all three features — energy, direction, time — to identify the source of each event.
Cite this article 5 formats
APA
Neutrino Times Editorial Team. (2026, May 21). Where do neutrinos come from? Every major source, in plain language. Neutrino Times. https://neutrino-times.com/articles/where-do-neutrinos-come-from/
Chicago
Neutrino Times Editorial Team. "Where do neutrinos come from? Every major source, in plain language." Neutrino Times, May 21, 2026. https://neutrino-times.com/articles/where-do-neutrinos-come-from/.
MLA
Neutrino Times Editorial Team. "Where do neutrinos come from? Every major source, in plain language." Neutrino Times, 21 May. 2026, https://neutrino-times.com/articles/where-do-neutrinos-come-from/.
BibTeX
@misc{neutrino-times-where-do-neutrinos-come-from,
author = {Neutrino Times Editorial Team},
title = {Where do neutrinos come from? Every major source, in plain language},
howpublished = {Neutrino Times},
year = {2026},
month = {may},
url = {https://neutrino-times.com/articles/where-do-neutrinos-come-from/},
note = {Accessed: 2026-05-21}
} RIS
TY - GEN TI - Where do neutrinos come from? Every major source, in plain language AU - Neutrino Times Editorial Team PY - 2026 DA - 2026-05-21 PB - Neutrino Times UR - https://neutrino-times.com/articles/where-do-neutrinos-come-from/ ER -