New research from the Norwegian University of Science and Technology may finally answer the question of the power source behind mysterious cosmic rays that have long perplexed astronomers.
Although often called “rays,” this cosmic radiation comprises highly accelerated small particles—primarily atomic nuclei—sent forth from parts of the universe that have long remained undetermined. Their intensity has led scientists to suspect that they have some relationship to the universe’s most extreme environments, such as neutron stars, black holes, or supernovae, with some cosmic rays displaying extraordinarily high energy levels.
Black Hole Winds
“We suspect that this high-energy radiation is created by winds from supermassive black holes,” said co-author Foteini Oikonomou, an associate professor at the NTNU Department of Physics.
Our Sun is just one of at least 100 billion stars within the Milky Way galaxy. At the center of our galaxy lies the Sagittarius A* black hole, which is currently relatively quiet due to a lack of nearby material to consume. However, many black holes across the universe are far more active, devouring matter equal to several Suns each year.
“A tiny portion of the material can be pushed away by the force of the black hole before it is pulled in,” said co-author Enrico Peretti from the Université Paris Cité. “As a result, around half of these supermassive black holes create winds that move through the universe at up to half the speed of light.”
A Potential Source of Cosmic Rays
Scientists first discovered these intense winds about a decade ago and found that their force could have galaxy-scale effects—such as halting star formation by dispersing interstellar gas. The NTNU researchers proposed that these winds might also produce smaller-scale phenomena, including cosmic rays. To test this, they developed an advanced computer model.
“It is possible that these powerful winds accelerate the particles that create the ultra-high-energy radiation,” said lead author Domenik Ehlert.
“The ultra-high-energy radiation consists of protons or atomic nuclei with energy up to 10²⁰ electron volts,” Oikonomou added. This represents an extraordinary amount of energy compressed into a tiny particle. If applied to something the size of a tennis ball, the same amount of energy could propel it at 200 kilometers per hour—about a billion times more energy than particles produced in the Large Hadron Collider.
Cosmic Radiation: A Cause for Concern
Despite their incredible power, cosmic rays are harmless to life on Earth, as the atmosphere destroys them before they can reach the ground—or even the cruising altitude of commercial airplanes. Still, there are important reasons to study them beyond pure scientific interest.
“For astronauts, cosmic radiation is a very serious problem,” Oikonomou emphasized.
“The main concern for astronauts is cosmic low-energy radiation produced by our own Sun, because it is much more common. The rays we study are infrequent enough that it is extremely unlikely they would pass through an astronaut,” she explained.
Comparisons to Earlier Work
Previous theories proposed other sources for cosmic rays, including starburst galaxies, gamma-ray bursts, and plasma outflows from black holes.
“All the other hypotheses are very good guesses—they are all sources that contain a lot of energy. But no one has provided evidence that any of them are the source. That is why we decided to investigate the winds from the supermassive black holes,” said Ehlert.
“We find that the conditions related to these winds align particularly well with particle acceleration. But we are still unable to prove that it is specifically these winds that accelerate the particles behind the high-energy cosmic radiation,” said Oikonomou.
Despite how well the model fits, one aspect remains unresolved. For cosmic rays in a specific energy range, the particles show a chemical composition that the current model cannot yet explain. Further studies will be necessary to uncover the complete origin story.
“We can also test the model using neutrino experiments,” Oikonomou added. “In the years to come, we hope to collaborate with neutrino astronomers to test our hypothesis.”
The paper “Ultra-high-energy Cosmic Rays from Ultra-fast Outflows of Active Galactic Nuclei” appeared on May 19, 2025, in Monthly Notices of the Royal Astronomical Society.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.