Ultraheavy nuclei may explain origins of highest-energy cosmic rays, Penn State study finds
By
Sam Sholtis
Crispy enough to crunch, soft enough to enjoy. A good bake.
Summary
New research led by Penn State scientists suggests that ultrahigh-energy cosmic rays—including the record-breaking "Amaterasu particle" detected in 2021—may consist of atomic nuclei heavier than iron. These ultraheavy nuclei lose energy more slowly than lighter particles as they travel through intergalactic space, allowing them to reach Earth at extreme energies. The findings, published in Physical Review Letters, could help narrow down the cosmic sources capable of accelerating these particles, such as neutron star mergers or collapsing massive stars. The research places new constraints on how ultraheavy nuclei contribute to the observed cosmic-ray population and may explain differences between northern and southern sky observations.
Key quotes
· 5 pulledUltrahigh-energy cosmic rays can only be accelerated by some of the most powerful sources in the universe.
The origins and acceleration mechanisms of ultrahigh-energy cosmic rays have been among the biggest mysteries in the field for more than 60 years, since the first example was reported.
Our research showed that at energies comparable to that of the Amaterasu particle, ultraheavy nuclei lose energy more slowly than protons or intermediate-mass nuclei, making them better able to survive cosmic distances and reach Earth at extreme energies.
We are not saying that all ultrahigh-energy cosmic rays are ultraheavy nuclei. But if some of the highest-energy events are ultraheavy nuclei, that would impact how we search for their sources.
The most promising sites for producing and accelerating such ultraheavy nuclei are massive star deaths involving explosive collapse into black holes or strongly magnetized neutron stars, as well as binary neutron-star mergers known to be powerful gravitational-wave emitters.
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