Blazars are active galactic nuclei with jets of magnetized plasma that point nearly along the line of sight. Most of the light from these extremely luminous objects is produced by high-energy particles. Although the jets are known to be ultimately powered by a supermassive black hole, how these particles are accelerated to such high energies has been an unanswered question. The Imaging X-Ray Polarimetry Explorer (IXPE), a collaboration between NASA...
