These particles make up about 90 percent of cosmic rays. For 10 points each:
[10e] What particles name the “chain” that low-mass stars use to fuse helium? One of these particles is equivalent to a hydrogen nucleus.
ANSWER: protons [accept proton–proton chain; prompt on p or p–p chain]
[10h] Protons can interact with photons to emit these particles, which is the basis for the GZK limit on the energy of cosmic rays. The electromagnetic component of cosmic ray air showers is produced when a neutral one of these particles decays into two photons.
ANSWER: pions [or pi mesons; prompt on mesons]
[10m] Proton–photon collisions can also form pions in these highly relativistic outflows pointed along the axes of active galactic nuclei. Blazars are quasars with one of these phenomena pointed towards Earth.
ANSWER: relativistic jets
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