Article: Birth zone shrinks for top cosmic rays.(Brief Article)

When cosmic rays, the universe's most energetic particles, pound into Earth's atmosphere, they unleash showers of particles streaking down with a dim, blue glow. Of these rays, those with the highest energy pepper the planet with the densest sprays over the widest areas, up to 10 kilometers across.

Astrophysicists have long pondered where and how the strongest cosmic rays acquire millions of times the energy that any earthbound particle accelerator can produce. Proposals on a growing list range from decaying superheavy particles in this galaxy to colliding cosmic strings of energy stretching across all of space.

If cosmic rays come from the farthest ...

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