Early galaxies discovered by the James Webb Space Telescope (JWST) may be bombarding Earth with high-energy neutrinos after a roughly 13-billion-year journey, according to a study led by Riku Kuze. These high-redshift objects, often dubbed “Little Red Dots,” could solve a long-standing astrophysics mystery regarding the origin of the all-sky neutrino background.
Detecting Neutrinos from Little Red Dots
Shortly after becoming operational, the James Webb Space Telescope focused its infrared optics on the early Universe. According to observations detailed in the research, astronomers identified an abundance of small red objects existing between 0.6 and 1.6 billion years after the Big Bang. Researchers theorize that these Little Red Dots (LRDs) contain growing supermassive black holes (SMBHs) at their centers, functioning essentially as early quasars.
These supermassive black holes are believed to be embedded in dense gaseous envelopes formed directly after massive gas clouds collapsed. According to an international team of researchers—including scientists from the Yukawa Institute for Theoretical Physics (YITP), Penn State’s Center for Multimessenger Astrophysics, Tohoku University, and Peking University—this dense environment creates ideal conditions for producing high-energy neutrinos.
Why Little Red Dots Hide Gamma Rays
Neutrinos are electrically neutral elementary particles created when high-energy particles like protons collide with surrounding matter or photons. While scientists routinely detect high-energy neutrinos on Earth, the exact source of their all-sky energy background remains unknown.
A major clue lies in the relationship between neutrinos and gamma rays. Astrophysical sources that produce high-energy neutrinos typically generate gamma rays as well. However, if all neutrinos came from standard luminous sources, the observed gamma-ray background would be significantly stronger than what instruments currently record. This discrepancy indicates that the true source must consist of hidden objects that successfully trap gamma rays.
Unlike typical active galactic nuclei, LRDs do not emit massive amounts of the radiation normally associated with jets or outflows from supermassive black holes. The research team theorizes that these jets are concealed entirely within the surrounding thick gas envelopes. As Riku Kuze explained in a Kyoto University press statement, abundant photons and dense gas are expected to exist around these black holes.
Numerical Calculations and Next Steps
To test their hypothesis, the international team used the observed luminosity and number density of LRDs to estimate their potential contribution to the all-sky neutrino background. They ran numerical calculations evaluating particle acceleration, secondary particle production, and cooling processes inside the gas envelopes.
The results demonstrate that if particle acceleration occurs in these concealed environments, LRDs can successfully produce high-energy neutrinos while suppressing gamma-ray emission. This indicates that LRDs contribute a fraction of the high-energy neutrinos currently reaching Earth.
Moving forward, the research team aims to estimate the precise ratio of different neutrino flavors and further investigate the physical conditions that keep jets concealed within these dense gaseous envelopes.
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