Sky Hotspots: The Senders of Ultra-Particles Identified express
Every day, particles with colossal energy enter Earth's atmosphere, like unsigned letters. Their source long remained a mystery. New research shows: these 'visitors' point to nearby galaxies, where from time to time catastrophes occur — collisions of neutron stars, ultra-dense spheres the size of a city but with the mass of the Sun. Upon impact, they scatter particles like postal items, and some fly straight to us.
The same model explains why the northern and southern hemispheres see a slightly different 'assortment' of particles: simply, the nearest 'post offices'—the sources — are located on different sides of the sky. Previously, it was thought that the composition of rays depends only on energy, but now it's clear: the key to the puzzle lies in the arrangement of the sender galaxies.
Original abstract
as written by the authors arXiv:2510.06193
The origin of ultra-high-energy cosmic rays remains one of the central open questions in astroparticle physics. Recent measurements reveal anisotropies in arrival directions, a rigidity-dependent composition dominated by intermediate-mass nuclei, and striking hemispheric differences in the energy spectra. Here we show that \emph{rare transients in nearby galaxies} can naturally account for these features. In our fiducial neutron-star merger model, the cosmic ray flux above $$25$$~EeV is dominated by ten nearby galaxies within $$8\,$$Mpc. This accounts for the observed hotspots: seven of the ten brightest galaxies coincide with reported excess regions, a chance probability of $$p\sim0.001$$. Nearby transients can also explain the spectral excess of TA over Auger and modify the rigidity--aligned succession of isotopes.
One such particle, smaller than an atom, carries energy comparable to a baseball's impact, like a carrier pigeon delivering a truck.