A newly discovered group of tiny red galaxies may help solve one of astronomy’s biggest mysteries: where the universe’s highest-energy neutrinos come from.
Using the James Webb Space Telescope, astronomers have found large numbers of distant galaxies known as Little Red Dots. These small, reddish galaxies formed in the early universe and appear to contain rapidly growing supermassive black holes at their centers.
A new study suggests that these hidden black holes could be producing some of the high-energy neutrinos that regularly pass through Earth.
The research, published in Physical Review D, offers a possible explanation for a mystery that has puzzled scientists for years.
Neutrinos are extremely tiny particles with almost no mass and no electric charge. Trillions of them pass through your body every second without you noticing because they rarely interact with matter. Scientists have detected very high-energy neutrinos arriving from deep space, but exactly where they come from has remained unknown.
Neutrinos are created when fast-moving particles, such as protons, collide with light particles or matter. These powerful collisions produce neutrinos that can easily escape into space, even from extremely dense environments.
However, there is a problem. These same collisions should also create large amounts of gamma rays, the most energetic form of light. If every source of high-energy neutrinos also released gamma rays freely, astronomers would observe far more gamma rays than they actually do. This means the true sources of many neutrinos must be hidden, allowing neutrinos to escape while trapping most of the gamma rays.
Researchers at Kyoto University believe the Little Red Dots may fit this description.
They suggest that at least some of these galaxies contain supermassive black holes surrounded by thick clouds of gas. Powerful jets launched by the black holes may remain buried inside these dense gas envelopes instead of breaking out into space. Inside these crowded environments, fast-moving particles would frequently collide with surrounding gas and light, producing large numbers of neutrinos.
Because the thick gas absorbs most of the gamma rays, very little high-energy light escapes. This matches what astronomers observe, making the idea an attractive explanation.
To test the theory, the research team estimated how many Little Red Dots exist and how bright they are. They also carried out detailed computer simulations to model how particles would be accelerated around the hidden black holes and how many neutrinos would be produced.
Their calculations suggest that if these buried black holes are indeed accelerating particles, the Little Red Dots could account for part of the high-energy neutrino background that reaches Earth.
The researchers do not believe these galaxies explain every cosmic neutrino, but they may be an important piece of the puzzle.
Because the Little Red Dots are extremely far away and hidden by dense gas, studying them directly is difficult. Future observations with more powerful telescopes and neutrino detectors will help scientists test the idea.
The next step is to study the different “flavors,” or types, of neutrinos reaching Earth and better understand how the black holes inside these tiny galaxies became surrounded by such thick gas.
Although many questions remain, the discovery suggests that some of the universe’s smallest and faintest galaxies may be quietly producing some of its most powerful particles.
Source: Kyoto University.
