Supermassive black holes at the centers of galaxies emit radiation and ultra-fast winds into space. Here is an artist's visualization. (Credit: NASA, JPL-Caltech)
In a nutshell
- Scientists discovered that ultra-fast winds around supermassive black holes could be launching the most energetic particles in the universe across space at nearly the speed of light.
- These cosmic particle accelerators may solve a long-standing mystery about where ultra-high-energy cosmic rays come from, filling a gap between particles from our galaxy and those from deep space.
- The research examined 86 real examples of these cosmic winds and found that about 5-15% could successfully accelerate particles to extreme energies, with one galaxy standing out as an ideal cosmic ray factory.
TRONDHEIM, Norway — Particles racing through space at nearly the speed of light pack energy millions of times greater than anything we can create on Earth. For decades, these cosmic bullets have puzzled scientists: where do they come from, and how do they get so powerful? New research points to violent winds surrounding supermassive black holes as the answer.
A team of international scientists found that ultra-fast outflows from active galaxies could be launching these mysterious particles, called ultra-high-energy cosmic rays, across the universe like cosmic particle accelerators.
These cosmic bullets are incredibly powerful. Back in 1962, scientists first detected one of these particles carrying an enormous amount of energy, about a hundred million times more energetic than the particles smashed in human-made colliders. To give you an idea of how much energy that is, if you could somehow harness it, a single particle could power a light bulb for about a second.
Researchers from Norwegian University of Science and Technology (NTNU) examined 86 observed ultra-fast outflows around supermassive black holes and found something remarkable: these cosmic winds could be the missing link in explaining where some of the universe’s most energetic particles come from. Their research is published in the Monthly Notices of the Royal Astronomical Society.
These ultra-high-energy particles are incredibly rare visitors to Earth. Scientists have to monitor huge areas of sky for weeks just to catch one. Between 2004 and 2007, researchers watching an area about the size of Rhode Island detected only 27 of these super-energetic particles, or roughly one every month.
How Black Hole Winds Become Cosmic Accelerators
Ultra-fast outflows are incredibly fast streams of matter expelled from regions around supermassive black holes. These winds reach velocities up to about 60% the speed of light, fast enough to circle Earth’s equator in about a tenth of a second. They carry enormous amounts of energy as they plow through space.
When these outflows slam into surrounding gas and dust, they create powerful shock waves that could accelerate particles to mind-boggling speeds. The process works like a cosmic pinball machine, where particles get bounced around and sped up by magnetic fields and shock waves until they’re moving at nearly the speed of light.
Lead researcher Domenik Ehlert and his colleagues used sophisticated 3D computer simulations to track how these particles would behave in these extreme environments. They discovered something interesting: while heavy particles like iron get destroyed by the intense radiation near black holes, lighter particles like protons can escape and keep their incredible energy.
Filling the Cosmic Ray Gap
Scientists have long known there’s a puzzling gap in where cosmic rays come from. On one end, we have cosmic rays from our own galaxy that max out at a certain energy level. On the higher end, we see extremely energetic particles that must come from outside our galaxy. But there’s been a missing piece in between that scientists call the “transition region.”
The team’s computer simulations showed that ultra-fast outflows can accelerate particles to energies that perfectly match what’s observed in this mysterious middle zone, potentially solving a puzzle that’s bothered scientists for years.
The researchers looked at real data from 86 observed ultra-fast outflows across the universe, studying their properties to see which ones would be the best at making high-energy particles.
Most of these outflows turned out to be too harsh for heavy particles to survive. The intense radiation from supermassive black holes destroys atomic nuclei before they can escape. However, the team found that about 5-15% of the outflows could successfully launch medium-weight particles like nitrogen and helium to very high energies.
Finding the Best Cosmic Particle Factories
One standout source emerged from their analysis: NGC 7582, a galaxy about 23 million light-years away. This relatively dim galaxy turned out to be ideal for making high-energy particles because its weaker radiation fields don’t destroy particles as easily as brighter galaxies do.
The research predicts that if these ultra-fast outflows are indeed major sources of ultra-high-energy cosmic rays, they should also produce ghostly particles called neutrinos. These neutrinos barely interact with matter, making them perfect messengers that can travel directly from where cosmic rays are born.
Current and future neutrino detectors like IceCube at the South Pole could test this prediction. If scientists detect the predicted neutrino signal, it would provide strong evidence that ultra-fast outflows are indeed cosmic particle accelerators.
The research tackles one of the biggest mysteries in space science: where do the most energetic particles in the universe come from? While we know that some cosmic rays come from exploding stars in our own galaxy, the ultra-high-energy ones must travel from much farther away.
Questions remain about exactly how common these ultra-fast outflows are and whether they can account for all the ultra-high-energy cosmic rays we observe. Future observations with better instruments will help test these predictions and improve our understanding of the universe’s most powerful particle accelerators.
For now, this study provides compelling evidence that some of the most energetic particles racing through space may have gotten their start in the violent neighborhoods around supermassive black holes — cosmic monsters that simultaneously destroy and create on an unimaginable scale.
Paper Summary
Methodology
The researchers used a combination of theoretical modeling and computer simulations to study how ultra-fast outflows from active galactic nuclei could accelerate cosmic ray particles. They analyzed a sample of 86 observed ultra-fast outflows, examining their properties like velocity, mass outflow rate, and the intensity of radiation fields around them. Using 3D Monte Carlo simulations with software called CRPropa, the team tracked how cosmic ray particles would behave as they’re accelerated and try to escape from these extreme environments. They specifically looked at five types of particles: protons, helium, nitrogen, silicon, and iron nuclei, calculating the maximum energies they could reach and how many would successfully escape.
Results
The study found that ultra-fast outflows can indeed accelerate cosmic ray particles to ultra-high energies, but with important limitations. While protons can escape these environments relatively easily and maintain high energies, heavier atomic nuclei like iron tend to get destroyed by intense radiation before they can escape. About 5-15% of the studied outflows could accelerate medium-weight particles like nitrogen and helium to very high energies above 10^17.6 electronvolts. The researchers determined that these outflows could explain the observed flux of cosmic rays in the “transition region” between galactic and extragalactic sources. One particular galaxy, NGC 7582, stood out as especially promising for producing ultra-high-energy particles due to its relatively weak radiation fields.
Limitations
Several important limitations affect this study. The sample of 86 ultra-fast outflows may not represent the entire population of such objects in the universe, particularly because it’s biased toward brighter, more easily detectable galaxies. The researchers had to make assumptions about uncertain parameters like the magnetic field strength and structure in these environments. Additionally, their mass outflow rate calculations showed that many sources would require more energy than the central black hole produces, suggesting either incomplete knowledge of these systems or that magnetic processes are more important than assumed. The study also focused only on one specific acceleration mechanism (wind termination shocks) and didn’t explore other possible ways these environments might accelerate particles.
Funding and Disclosures
Agence Nationale de la Recherche supported this research (grant ANR-21-CE31-0028). The authors thank several colleagues for helpful discussions and assistance with the compiled ultra-fast outflow samples. No conflicts of interest were disclosed in the paper.
Publication Information
This research was published in Monthly Notices of the Royal Astronomical Society, Volume 539, pages 2435–2462, in 2025. The paper was accepted on March 17, 2025, and published online with advance access on March 19, 2025. The DOI is https://doi.org/10.1093/mnras/staf457. The lead author is Domenik Ehlert from the Norwegian University of Science and Technology, with co-authors Foteini Oikonomou (also at NTNU) and Enrico Peretti from CNRS, Astroparticule et Cosmologie, Université Paris Cité.
