New findings indicate that ultra-high energy cosmic rays gain their power from magnetic turbulence.
Ultra-high energy cosmic rays, which originate in extremely intense astrophysical settings—such as the chaotic regions around black holes and neutron stars—possess significantly more energy than the energetic particles produced by our sun. These cosmic rays carry approximately 10 million times the energy of particles produced in Earth’s most powerful particle accelerator, the Large Hadron Collider.
But where does all this energy come from? For many years, scientists thought that the energy originated from shocks in extreme astrophysical scenarios, like when a star explodes before forming a black hole, which can disperse particles in a massive explosion.
While that theory seemed reasonable, new research published this week in The Astrophysical Journal Letters suggests a different explanation for these observations. The study indicates that magnetic turbulence is a more likely source of the cosmic rays’ energy. Researchers discovered that in these extreme environments, magnetic fields twist and tangle, which accelerates particles rapidly and increases their energy dramatically until it reaches a sharp limit.
“These results address long-standing questions that interest both astrophysicists and particle physicists regarding how these cosmic rays obtain their energy,” stated Luca Comisso, an associate research scientist at the Columbia Astrophysics Lab and one of the study’s authors.
This study builds on earlier research from last year by Comisso and colleagues concerning the energetic particles emitted by the sun, which they also found originate from magnetic fields in the sun’s corona. In that earlier study, they identified better methods to predict the emergence of these energetic particles.
Ultra-high energy cosmic rays are vastly more powerful compared to particles emitted by the sun, reaching up to 1020 electron volts, whereas solar particles can reach about 1010 electron volts, representing a difference of ten orders of magnitude. (To illustrate the scale of this difference, think of a grain of rice weighing about 0.05 grams compared to a 500-ton Airbus A380, the largest passenger airplane in the world.) “Interestingly, despite their vast differences, both environments have highly tangled magnetic fields, and this tangled characteristic is crucial for energizing particles,” Comisso remarked.
“Notably, the data for ultra-high energy cosmic rays strongly supports the predictions made about magnetic turbulence rather than shock acceleration. This represents a significant advancement for the field,” added Glennys R. Farrar, a co-author of the paper and a professor of physics at New York University.
The research was funded by the National Science Foundation.
