ALMA Lensing Data Show Starburst Core in JCMT0402−0424 Powers Neutrino Event IC 210922A

The international team used ALMA plus optical and X-ray follow-up to exploit a foreground lens that magnified the background source by a factor of ~8. High-resolution 870-micron imaging resolved a compact, dust-obscured core with star-formation surface density exceeding 1000 solar masses per year per square kiloparsec and no detectable radio jet or hard X-ray point source. Absence of AGN signatures rules out the supermassive black hole accelerator previously assumed for most IceCube-associated galaxies.

This result aligns with earlier IceCube stacking analyses that found a 2.5-sigma excess from infrared-luminous starbursts, yet lacked individual source identifications. It also matches theoretical predictions from models in which cosmic-ray protons accelerated by supernovae and stellar winds interact with dense molecular gas to produce neutrinos at PeV energies. The 20 percent contribution estimate for the diffuse neutrino background follows directly from scaling the observed star-formation rate density to the full population of similar compact cores.

Confirmation requires both deeper X-ray limits below 10^43 erg/s and neutrino timing correlations with future starburst flares. A statistically robust sample of ten lensed starbursts observed with ALMA and IceCube-Gen2 would test whether the neutrino yield scales linearly with star-formation rate above 500 solar masses per year.