Identifying the origins of high-energy neutrinos arriving from space is one of the most important challenges in modern astronomy. A few relatively nearby active galaxies have been identified as sources of neutrino emissions. However, the small number of sources identified so far cannot account for the total amount of neutrinos arriving from across the Universe. Astronomers have therefore suspected that other major source populations remain hidden.
The epoch about 10 billion years ago, when galaxies were forming stars most actively in the history of the Universe, is known as “Cosmic Noon.” Theoretical studies have suggested that these galaxies produced large numbers of cosmic rays, and they may be major contributors to the cosmic neutrino background. However, these galaxies are at cosmological distances and often deeply hidden behind thick layers of dust, making it extremely difficult to identify individual galaxies as counterparts to specific neutrino events

The international research team, led by Yuji Urata (MITOS Science Co., LTD. / National Central University, Taiwan) and Kuiyun Huang (Chung Yuan Christian University, Taiwan), and including Shigeo Kimura (Tohoku University), Yusuke Miyamoto (Fukui University of Technology), and researchers at the National Astronomical Observatory of Japan, carried the follow-up radio observations using James Clerk Maxwell Telescope (JCMT) and Submillimeter Array (SMA) toward the arrival direction of the high-energy neutrino event IC 210922A, detected by the IceCube Neutrino Observatory at the South Pole. They found a submillimeter source, JCMT0402−0424. The multi-wavelength follow-up also made use of NASA’s Neil Gehrels Swift Observatory. Swift/XRT observations and long-term Swift/BAT monitoring found no compelling X-ray counterpart associated with IC 210922A. Drawing on the team’s long-standing experience in rapid follow-up observations of high-energy transients, including gamma-ray bursts and jetted tidal disruption events, these Swift data helped the team rule out other plausible high-energy electromagnetic counterparts in the IceCube localization region.

High-resolution observations with ALMA revealed an arc-like, multiply imaged structure distorted by gravitational lensing caused by a foreground elliptical galaxy. JCMT0402−0424 is an extremely bright galaxy in the early Universe, about 11 billion years ago. Such a powerful energy source would usually suggest activity powered by a supermassive black hole, or a high-energy transient phenomenon such as a tidal disruption event. Indeed, several previously reported or discussed neutrino-source candidates are associated with active galactic nuclei or tidal disruption events. In contrast, this source shows no strong X-ray or gamma-ray emission characteristic of dominant black-hole activity or a high-energy transient. Deeply embedded in dense dust and invisible at optical wavelengths, it has been nicknamed “Shadow Blaster.”

A conceptual figure of this study. ALMA captured the starburst galaxy “Shadow Blaster” in the same direction as the high-energy neutrino event IC 210922A. Actual radio observations by ALMA are shown in the zoom-in inset. Due to gravitational lensing, the ALMA observations show four distorted images of Shadow Blaster, which has been identified as the source of the neutrinos (indicated by the Greek letter nu). An artist’s conception of Shadow Blaster’s true appearance is shown in the circle. (Credit: MITOS)

Thanks to gravitational lensing, the galaxy image was magnified and enhanced. The team was able to study the internal structure of this dusty star-forming galaxy in the early Universe in detail, which is ordinarily unseen, by modeling the lensing effect of the foreground elliptical galaxy based on optical and infrared data from the Subaru Telescope and the Gemini Telescope. Moreover, the detailed analysis of ALMA measurements of the carbon-monoxide (CO) molecular gas energy distribution (SLED) showed no clear signature of gas heated by a dominant active black hole; instead, the observations indicate that the gas is most likely heated by “intense star formation”. The analysis revealed that the central region of this galaxy contains a “compact core”, where a large amount of gas and dust is packed into a region only about 1,500 light-years across.

Such an extremely high-density environment can act as a natural particle accelerator, where energetic particles repeatedly collide with gas and produce neutrinos. The neutrino emission from any single galaxy is expected to be very weak; however, a population of compact dusty starburst galaxies undergoing intense star formation may contribute a significant fraction, possibly up to ~20%, of the high-energy neutrino background.

The team has been investigating the acceleration site of high-energy particles in cosmic explosions by millimeter and submillimeter observations, especially by polarimetry for a peculiar explosion or a Gamma-Ray Burst afterglow. (Refer to: [ALMA Discoveries] ALMA Reveals Origin of Mysterious Blast: AT2018cow originated from supernova in a strongly-magnetized, dense environment (2019.11.18), Measuring Gamma-Ray Bursts’ Hidden Energy Unearths Clues to the Evolution of the Universe (2022.12.9)). Throughout those studies, ALMA shows excellent capabilities to uncover the hidden structures in high-energy objects, which are difficult to see in visible light or X-rays, such as dense gas and dust, magnetism or compact emission regions.

A video combining multi-wavelength images. As the view zooms in on a galaxy cluster observed by the Gemini North Telescope in optical and infrared wavelengths, a massive elliptical galaxy (red) comes into view. ALMA observations in the submillimeter wavelength range reveal a distant galaxy, which appears distorted into an arc and split into multiple images due to the gravitational lensing effect caused by the elliptical galaxy (yellow). (Credit: NOIRLab)

For this video, please refer to NOIRLab’s Science Release: Tracing a Neutrino Ghost to Distant “Shadow Blaster” Galaxy,

Key Words
•IceCube: The world’s largest “neutrino detector” with a volume of 1 km3, constructed deep in the ice floor of Antarctica. It is expected to play a key role in exploring the mysteries in energetic phenomena, such as black holes and supernovae, by detecting neutrinos, invisible particles from cosmic origin.

• IC 210922A: A high-energy neutrino event detected by IceCube at 18:17:20.948 on September 22, 2021 (UT). As it was likely to have a cosmic origin, several telescopes worldwide targeted this event for follow-up observations. The estimated energy was about 750 TeV, corresponding to tens of millions of times higher than the energies of neutrinos detected from SN 1978A.

• Multi-messenger Astronomy: A method of astronomy study combining “various messengers” from the Universe, not only electromagnetic waves (light), which have been used for traditional astronomical observation, but also the gravitational waves and particles (such as neutrinos).

Publication
This research was published in a paper titled “Compact dusty starbursts at cosmic noon linked to high-energy neutrinos” by Urata et al., in Nature Astronomy on June 17, 2026.
DOI: 10.1038/s41550-026-02884-9

Support
This research was supported by JSPS KAKENHI (Numbers JP23K03449, JP23H04899, JP26K00733, JP26K00750), and Tohoku Initiative for Fostering Global Researchers for Interdisciplinary Sciences (TI-FRIS)..

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organization for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning, and operation of ALMA.