Neutrinos are not exotic to produce. Any process governed by the weak nuclear force creates one, and that force is involved in a great many of the universe’s everyday workings — from the fusion that lights the Sun to the radioactive decay of a banana’s potassium-40. The result is a universe positively filled with neutrinos, and a detection problem made out of just how unfussily they pass through everything afterward.
This article tours the main ways neutrinos come into existence — the everyday, the astrophysical, the manufactured, and the cosmological — and gives a sense of the relative numbers each produces.
The unifying mechanism: the weak interaction
Every fundamental way of producing a neutrino involves the weak nuclear force. Concretely, the simplest version is beta decay: a neutron inside a nucleus converts into a proton, ejecting an electron and an electron antineutrino:
n → p + e⁻ + ν̄_e
The companion process, called inverse beta decay, runs the other way — typically when a proton captures an electron:
p + e⁻ → n + ν_e
And the high-energy version is the decay of a pion (a short-lived particle produced in cosmic-ray showers and in accelerator beams):
π⁺ → μ⁺ + ν_μ
Different sources emphasise different versions of these processes, but all of them are different faces of the same underlying weak interaction. For the wider picture, see our what-is-a-neutrino explainer and the neutrino-vs-antineutrino comparison.
The Sun: where most of your neutrinos come from
The dominant neutrino source on Earth is, by a vast margin, the Sun. The proton-proton fusion chain that keeps the Sun shining produces electron neutrinos at every step, with the simplest reaction being:
p + p → ²H + e⁺ + ν_e
About 65 billion solar neutrinos pass through every square centimetre of your body, every second of every day. Day or night, indoors or outdoors, lead-walled basement or open field. The detection rate that any of them interact with you is negligible — but the flux is enormous.
For more on the Sun’s role as a neutrino factory, see our solar-neutrinos hub and the standard solar model explainer.
Cosmic rays in the atmosphere
A second steady source comes from above: atmospheric neutrinos, produced when high-energy cosmic-ray protons strike air molecules in the upper atmosphere. The collisions create pions and kaons, which decay in flight to produce electron and muon neutrinos:
π⁺ → μ⁺ + ν_μ → e⁺ + ν_e + ν̄_μ + ν_μ
The atmospheric neutrino flux at Earth’s surface is much smaller than the solar flux — at the megaelectronvolt-to-gigaelectronvolt energies of interest, perhaps one neutrino per square centimetre per second — but it spans a broader range of energies, including the high-energy end that solar neutrinos do not reach. Atmospheric neutrinos were the key to the 1998 discovery of neutrino oscillation at Super-Kamiokande.
For the deeper background, see our atmospheric flux explainer.
Nuclear reactors
Every operating nuclear reactor on the planet produces an enormous flux of electron antineutrinos — about 2 × 10²⁰ per second per gigawatt of thermal power, from the beta decays of fission fragments. This is how Reines and Cowan first detected the neutrino in 1956 at the Savannah River reactor, and how reactor experiments since — KamLAND, Daya Bay, RENO, JUNO — have refined the picture of oscillation.
Reactor antineutrinos are also useful for reactor monitoring as a non-proliferation tool, one of the few practical applications of neutrino physics.
Particle accelerators (the manufactured neutrino)
When physicists want a controlled neutrino source, they build one. A particle accelerator delivers a high-intensity proton beam onto a target; the collision produces a spray of pions and kaons; magnetic focusing horns sort them; and a long decay tunnel lets them decay in flight, producing a directed beam of neutrinos aimed at a distant detector.
This is the setup for T2K (Japan), NOvA (USA), MINOS, and the upcoming DUNE (Fermilab to South Dakota). For the mechanics in detail see our what-is-a-neutrino-beam explainer. Accelerators are not the largest neutrino source by flux, but they are the only source whose energy, direction, flavour mix, and timing the experimenter chooses.
Supernovae: the brightest source the universe has
When a massive star runs out of fuel, its iron core collapses gravitationally in a fraction of a second. The collapse releases about 10⁵⁸ neutrinos in a burst of a few seconds — more energy in neutrinos than the entire visible-light output of the Sun across its lifetime.
We’ve witnessed this once in modern times. SN 1987A, in the Large Magellanic Cloud, fired about 24 neutrinos into terrestrial detectors over a few seconds, marking the birth of neutrino astronomy. The next nearby supernova is expected to deliver many thousands of neutrinos into modern detectors like Super-K, JUNO, and DUNE.
The cumulative emission from all past supernovae across cosmic time is called the diffuse supernova neutrino background — and detecting it is one of the targets of current and next-generation experiments. See our DSNB explainer.
Cosmic accelerators
Beyond supernovae, the highest-energy neutrinos come from cosmic accelerators around active galactic nuclei, blazar jets, supernova remnants, and similar extreme environments. Cosmic-ray protons accelerated in these regions collide with ambient gas or photons and produce pions, whose decays emit ultra-high-energy neutrinos.
These are the neutrinos IceCube has been catching one by one — the 2017 association with TXS 0506+056, the 2022 steady excess from NGC 1068, the 2023 diffuse emission from the galactic plane. The mechanism is the same pion-decay chain as in atmospheric neutrinos and accelerator beams, just at petaelectronvolt rather than gigaelectronvolt energies.
The Big Bang: relic neutrinos
The earliest neutrinos in the universe were produced about one second after the Big Bang, when the universe cooled enough for them to decouple from ordinary matter. They have been cruising through space ever since, redshifting along with the rest of the universe.
Today the cosmological neutrino background has a temperature of about 1.95 kelvin and a density of about 336 per cubic centimetre. They are everywhere — but their energies are so low that no detector has yet directly observed them. Their indirect imprint on the cosmic microwave background and on the growth of structure provides one of the precision tests of standard cosmology. See our relic-neutrinos explainer.
A rough flux ranking
Here is a back-of-envelope ordering of the neutrino sources Earth is exposed to, by flux at our location:
| Source | Approximate flux |
|---|---|
| Cosmological relic | ~336 per cm³ (everywhere, very low energy) |
| Solar | 65 billion / cm² / s |
| Atmospheric | ~1 / cm² / s |
| Reactor (within a few km of a nuclear plant) | ~10⁸ / cm² / s near a reactor |
| Diffuse supernova background | ~10 / cm² / s |
| Astrophysical (high-energy) | ~10⁻¹¹ / cm² / s above 100 TeV |
The numbers span twenty-five orders of magnitude — but each source has its own role in the science of neutrino physics. Detectors are designed to be sensitive in the energy band and direction where one or two of these sources dominate. See our sources-of-neutrinos series for the full breakdown.
The takeaway
A neutrino is created any time the weak nuclear force acts in a way that turns one kind of particle into another. The Sun makes them in fusion, the atmosphere makes them from cosmic rays, reactors make them from fission fragments, accelerators make them on demand, supernovae make them by the trillion, and the Big Bang made the rest. Together those sources produce a universe so full of neutrinos that the question is not “where do they come from” — it is “how do you ever see one.” For that side of the story, see our why-are-neutrinos-hard-to-detect explainer.
Related reading: What is a neutrino?, Where do neutrinos come from?, Sources of neutrinos, part 1: solar.
Frequently asked
Where do most of the neutrinos hitting Earth come from?
From the Sun. Solar fusion in the core produces electron neutrinos at a rate that, scaled to Earth's distance, gives a flux of about 65 billion neutrinos per square centimetre per second. The next-largest contributors at our latitude are the atmospheric neutrinos produced when cosmic rays strike air molecules, and reactor antineutrinos near nuclear power plants — both several orders of magnitude smaller than the solar flux.
What physical process actually creates a neutrino?
Any process governed by the weak nuclear force. The two commonest are beta decay, where a neutron converts into a proton plus an electron plus an antineutrino, and inverse beta decay, where a proton plus an electron convert into a neutron plus a neutrino. Particle accelerator beams produce neutrinos by colliding protons with a target to make pions, which decay into muons and neutrinos. All these are different faces of the same weak interaction.
Can neutrinos be produced in a laboratory?
Yes, in many ways. Nuclear reactors produce trillions of antineutrinos per second through routine beta decays of fission fragments. Particle accelerators produce focused neutrino beams aimed at distant detectors — T2K, NOvA, the upcoming DUNE. Some experiments use radioactive sources to produce neutrinos for calibration. In short, neutrinos are not exotic to produce — they are just hard to detect.
Did the Big Bang create neutrinos that still exist today?
Yes. The first second after the Big Bang produced a vast population of neutrinos that decoupled from ordinary matter when the universe was about one second old. These cosmological relic neutrinos still permeate space at a density of about 336 per cubic centimetre, but their energies are so low — corresponding to a temperature of about 1.95 kelvin — that they have never been directly detected. Their indirect imprint on the cosmic microwave background and on the growth of structure is one of the most precise tests we have of standard cosmology.
Which natural sources produce the highest-energy neutrinos?
Supernovae produce a burst of neutrinos in the tens of megaelectronvolts. Cosmic accelerators around active galactic nuclei and supernova remnants reach much further: up to the petaelectronvolt scale, as detected by IceCube. The highest-energy neutrinos known were produced by extragalactic sources whose exact identification is one of the active research frontiers in neutrino astronomy.
Cite this article 5 formats
APA
Neutrino Times Editorial Team. (2026, June 14). How are neutrinos created?. Neutrino Times. https://neutrino-times.com/articles/how-are-neutrinos-created/
Chicago
Neutrino Times Editorial Team. "How are neutrinos created?." Neutrino Times, June 14, 2026. https://neutrino-times.com/articles/how-are-neutrinos-created/.
MLA
Neutrino Times Editorial Team. "How are neutrinos created?." Neutrino Times, 14 Jun. 2026, https://neutrino-times.com/articles/how-are-neutrinos-created/.
BibTeX
@misc{neutrino-times-how-are-neutrinos-created,
author = {Neutrino Times Editorial Team},
title = {How are neutrinos created?},
howpublished = {Neutrino Times},
year = {2026},
month = {jun},
url = {https://neutrino-times.com/articles/how-are-neutrinos-created/},
note = {Accessed: 2026-06-14}
} RIS
TY - GEN TI - How are neutrinos created? AU - Neutrino Times Editorial Team PY - 2026 DA - 2026-06-14 PB - Neutrino Times UR - https://neutrino-times.com/articles/how-are-neutrinos-created/ ER -