A more than 60-year mystery about the origin of ultra-high-energy cosmic rays might be solved by a new theory.

Ultra-high-energy cosmic rays (UHECRs) are the highest-energy particles in the universe. The energies of these beams are more than a million times greater than the highest energies that humans can create.

“After 6 decades of effort, the origin of the mysterious highest-energy particles in the universe may finally have been identified,” says Glennys Farrar from New York University.

Farrar is the author of a paper published in the journal Physical Review Letters which suggests a testable explanation for how UHECRs are created.

Her theory is that UHECRs are accelerated in the turbulent magnetic outflows caused by the violent mergers of binary neutron stars. The UHECRs are spewed out just before the collision leads to the formation of a black hole.

This process is so powerful that it creates gravitational waves strong enough to be detected using current technology.

“This insight gives a new tool for understanding the most cataclysmic events of the universe: 2 neutron stars merging to form a black hole, which is the process responsible for the creation of many precious or exotic elements, including gold, platinum, uranium, iodine, and xenon,” Farrar adds.

Farrar’s analysis includes 2 outcomes that can be tested using observations.

One is that the highest-energy UHECRs are the result of rare events which produce “r-process” elements such as xenon and tellurium. Astronomers can now look for signals of these elements in UHECR data.

The other is that extremely high-energy neutrinos that come from UHECR events should be accompanied by gravitational waves from the neutron star collision.

Farrar’s explanation that UHECRs are produced by binary neutron star mergers is the first to explain 2 of the most mysterious features of these high-energy particles. One is the correlation between the energy of an UHECR and its electric charge, and the other is the extraordinarily high energy of some of these events.