Can distant blazars explain the universe's most energetic cosmic rays?

HSP BL Lacs are supermassive black hole jets that accelerate electrons to extraordinary speeds, producing X-rays and UV light. A 2017 neutrino detection from blazar TXS 0506+056 suggested these objects generate ultra-high-energy cosmic rays and neutrinos, but new data reveal inconsistencies: the extreme mass needed to power both cosmic rays and neutrinos strains physics, and cosmic ray arrival patterns don't match what rare beamed sources should produce. Next-generation detectors will test whether blazars are truly the culprits.