Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have tracked down the source of a powerful neutrino burst with the help of a remarkable cosmic phenomenon that acted like a natural telescope. What they discovered challenged expectations.
Researchers initially suspected that a supermassive black hole was powering an extraordinarily bright distant galaxy linked to the neutrino signal. Instead, observations revealed that the galaxy's energy comes from intense star formation. The finding provides important evidence that could help explain where many of the Universe's mysterious high-energy neutrinos originate.
Tracking One of the Universe's Most Elusive Particles
Neutrinos are among the most puzzling particles known to science. Vast numbers of them pass through space, and even through Earth, with very little interaction with matter. Although astronomers have identified a handful of galaxies capable of producing neutrinos, those known sources are not enough to account for the large population of high-energy neutrinos detected so far.
To investigate the origin of one such particle, an international team of researchers from MITOS Science Co., LTD., National Central University, Chung Yuan Christian University, Tohoku University, Fukui University of Technology, and the National Astronomical Observatory of Japan conducted follow-up observations using ALMA and several other telescopes.
Their target was the high-energy neutrino event IC 210922A, which was detected by the IceCube Neutrino Observatory at the South Pole. The search led them to an exceptionally luminous galaxy known as JCMT0402−0424, located roughly 11 billion light-years from Earth.
The Mystery of Shadow Blaster
Previously identified neutrino-producing galaxies have typically been powered by supermassive black holes. However, when the researchers examined JCMT0402−0424, they found no evidence of the energetic emissions normally associated with such a black hole.
The galaxy is heavily veiled by dust, making it difficult to see in visible light. At submillimeter wavelengths, however, it shines intensely. Because of its hidden nature and extreme brightness at those wavelengths, the team gave it the nickname 'Shadow Blaster.'
A Natural Telescope Reveals the Galaxy's Core
Astronomers were able to look deep inside Shadow Blaster thanks to a fortunate alignment with another galaxy positioned between it and Earth. The foreground galaxy's gravity bent and amplified radio waves coming from Shadow Blaster, effectively creating a natural telescope.
This gravitational lensing effect produced brighter and enlarged images that allowed ALMA to examine the distant galaxy in far greater detail.
The radio observations again showed no sign of a powerful black hole. Instead, the data pointed toward another source of energy. The gas and dust throughout the galaxy appear to be heated primarily by vigorous star formation.
Researchers also identified a dense "compact core" at the center of Shadow Blaster. Large quantities of gas and dust are packed into a region only about 1,500 light-years across. Such an extreme environment is capable of generating neutrinos.
A New Explanation for High-Energy Neutrinos
The results suggest that intense star-forming galaxies may represent an important and previously underappreciated source of high-energy neutrinos.
According to the team, compact, dust-rich starburst galaxies undergoing rapid star formation could contribute a substantial share of the high-energy neutrino background. Their analysis indicates that these galaxies may account for as much as 20% of the total population of high-energy neutrinos observed across the Universe.
If confirmed by future studies, the discovery could significantly reshape scientists' understanding of how some of the Universe's most elusive particles are produced.
