Why a distant quasar's radio core is mysteriously weak on magnetism

3C 138, a distant quasar that erupted in radio and gamma rays in 2022, reveals an unusual magnetic environment in its compact radio core. Using radio telescopes across multiple frequencies, researchers measured the magnetic field strength via synchrotron radiation and compared it to theoretical equipartition expectations, finding the actual field is only about 5% as strong. This particle-dominated, weakly magnetized core can still produce X-rays and gamma rays through inverse Compton scattering when shocks accelerate particles—a cleaner picture than requiring exotic relativistic beaming.