A giant neutrino that slammed into Earth in September 2021 has finally been traced back to its source: a dusty, compact galaxy about 13 billion light years away, invisible to most optical telescopes and busy making stars at a ridiculous pace. The signal, known as IC 210922A, carried an estimated energy of about 750 TeV, putting it among the most energetic neutrino events ever recorded.
This IceCube neutrino came from JCMT0402-0424, a hidden galaxy that only stood out once astronomers used submillimetre and radio data. The result helps show how some of the universe’s most energetic particles can be traced to sources that are nearly impossible to spot in visible light.
How IceCube followed the trail
The IceCube observatory in Antarctica first picked up the neutrino, then astronomers went hunting with NASA’s Fermi and Swift telescopes. That search came up empty in the Eridanus region, which is hardly unusual: high-energy neutrinos are elusive by design, and their sources are often buried behind layers of astrophysical noise.
The breakthrough came from data taken by the James Clerk Maxwell Telescope and the Submillimetre Array in Hawaii. Those instruments revealed a previously unknown galaxy, JCMT0402-0424, hidden inside thick clouds of gas and dust and therefore nearly invisible in ordinary light. Gravitational lensing from another galaxy along the same line of sight helped make the detection possible. Astronomy does love a workaround.
A small galaxy making stars at breakneck speed
JCMT0402-0424 may be compact, but it is anything but sleepy. Researchers say it is forming new stars tens to hundreds of times faster than the Milky Way, and its central region appears packed with extremely dense gas and dust clouds. That combination makes it a plausible engine for a powerful neutrino outburst.
- Event: IC 210922A
- Detected by: IceCube
- Estimated energy: about 750 TeV
- Source galaxy: JCMT0402-0424
- Distance: about 13 billion light years
IceCube neutrino source and the diffuse particle flux
The bigger implication is that galaxies like this may be doing more heavy lifting in the neutrino sky than astronomers once thought. The researchers estimate that up to 20% of the diffuse particle flux seen by IceCube could come from distant systems of this kind, which would make dusty starbursts a far more important piece of the puzzle than the brighter, cleaner objects often get credit for.
That also points to a familiar problem in high-energy astronomy: the universe rarely hands over its answers in visible light. If more hidden galaxies are out there producing neutrinos at similar rates, the next breakthrough may come not from a single telescope, but from combining the boringly named instruments that can see through the mess. And there is plenty of mess left to scan.