Ultrahigh-energy cosmic Rays (UHECRs) are the highest-energy particles in the universe, whose energies are more than a million times what humans can achieve. While UHECRs have existed for 60 years, researchers have not formulated a satisfactory explanation for their origin that explains all the observations.
However, a new theory introduced by New York University physicist Glennys Farrar provides a viable and testable explanation for how UHECRs are created.
The theory suggests that ultrahigh-energy cosmic rays (UHECRs) are produced in binary neutron star (BNS) mergers. This insight offers a new tool for understanding the most cataclysmic events of the universe: two 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.
The work suggests that ultra-high-energy cosmic rays (UHECRs) are accelerated in the turbulent magnetic outflows of Binary Neutron Star mergers. These outflows occur before the final black hole formation and generate powerful gravitational waves, some of which scientists have detected at the LIGO-Virgo collaboration.
Farrar’s proposal in Physical Review Letters explains two mysterious features of UHECRs for the first time: the strong link between a UHECR’s energy and its electric charge and the extremely high energy of a few rare events.
Farrar’s analysis leads to two key points for future experimental validation:
The highest-energy ultra-high-energy cosmic rays (UHECRs) come from rare “r-process” elements like xenon and tellurium. This suggests searching for these elements in UHECR data.
Extremely high-energy neutrinos, resulting from UHECR collisions, are always accompanied by the gravitational waves produced in the parent neutron star merger.
Journal Reference:
- Glennys R. Farrar, Binary Neutron Star Mergers as the Source of the Highest Energy Cosmic Rays, Physical Review Letters (2025). DOI: 10.1103/PhysRevLett.134.081003
