Scientists may have linked a high-energy neutrino detected on Earth to a galaxy more than 11 billion light-years away, a discovery that could explain where the universe’s most powerful neutrinos are produced.
(CN) – Every second, trillions of tiny particles called neutrinos pass through your body unnoticed. They carry no electrical charge, have almost no mass, and rarely interact with anything around them.
Scientists have discovered them for decades, but where the most powerful ones come from has remained a mystery.
Now, a team of astronomers may have found an answer.
In one study published Wednesday in the journal Nature Astronomy, researchers led by Yuji Urata of MITOS Science Co. Ltd. in Taiwan say a distant galaxy nicknamed the “Shadow Blaster” is the strongest candidate yet for the source of a high-energy neutrino detected in 2021.
The galaxy is located about 11 billion light years from Earth. If the link holds, it would be the first time a star-forming galaxy has been directly associated with a high-energy neutrino event.
In 2021, the IceCube Neutrino Observatory in Antarctica detected a high-energy neutrino known as IC 210922A. IceCube alerted the scientific community, and multiple teams tried to find a source, scanning the region of the sky from which the neutrino appeared to come using gamma-ray, X-ray, and optical telescopes. None found a convincing explanation.
A few days later, Urata’s team pointed two telescopes atop Maunakea in Hawaii at the same part of the sky and spotted the Shadow Blaster. His position and unusual brilliance immediately caught the attention of the team.
Shadow Blaster is one of the brightest known star-forming galaxies in the universe, emitting approximately 2.7 trillion times more infrared light than the sun. Astronomers found no evidence that an active black hole is powering that outflow. Instead, they say the energy comes from an intense burst of star formation packed into a compact, dust-filled core.
This environment may be just what neutrino theorists have been looking for. Models suggest that high-energy particles can be trapped inside dense clouds of gas and dust, repeatedly colliding and producing neutrinos before escaping into space.
“Shadow Blaster possesses the kind of dense, gas-rich environment that theoretical models have long suggested could efficiently produce high-energy neutrinos,” Urata said. “If confirmed, Shadow Blaster would be the first individual dusty, star-forming galaxy directly associated with a high-energy neutrino event.”
Studying the Shadow Blaster in detail required a lucky break.
The galaxy lies behind a massive elliptical galaxy whose gravity bends and magnifies the light behind it, a phenomenon known as gravitational lensing. The effect increased the Shadow Blaster’s apparent brightness to about 33 trillion times that of the sun, making it easier to study in detail.
To take advantage of this magnification, the team had to understand the foreground galaxy itself, measuring its distance, mass and structure. They did this using two instruments on the Gemini North telescope in Maunakea.
“The combined GMOS and GNIRS data helped us measure the distance to the lensed galaxy and determine that it is a massive elliptical galaxy,” Urata said. “This information was essential for estimating the lensing mass distribution and building a model of gravitational lensing.”
With that model in hand, the team used the Atacama Large Millimeter/submillimeter Array in Chile to peer into the Shadow Blaster’s core and confirm just how compact and dense it is.
Shadow Blaster may also explain where many of the universe’s high-energy neutrinos come from. About 10 billion years ago, the universe was full of galaxies like it, all forming stars at a frantic pace.
Scientists have long suspected that these galaxies were producing large numbers of neutrinos, but finding direct evidence has been difficult because they are so distant and shrouded in dust.
“This discovery shows how particle detectors and telescopes become much more powerful when they work together, opening a powerful multi-messenger window on the universe,” said Martin Still, program director in NSF’s Office of Research Infrastructure.
If the researchers are right, galaxies like Shadow Blaster could account for a significant fraction of the high-energy neutrinos arriving at Earth from across the cosmos. The team suggests they could produce roughly one-fifth of the diffuse neutrino background measured by IceCube.
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