An important discovery comes from space thanks to the Imaging X-ray Polarimetry Explorer (IXPE) mission led by NASA and the Italian Space Agency: X-rays emitted by relativistic blazar jets are produced by high-speed electrons interacting with photons. This was revealed by observations of blazar BL Lacertae, a celestial object with one of its jets oriented toward Earth, studied for one week in November 2023. The data, published in The Astrophysical Journal Letters, show a strong discrepancy between the polarization of optical light (47.5%) and that of X-rays (7.6%). This gap confirms the role of Compton scattering, a process in which infrared photons, struck by energetic electrons, acquire the energy needed to transform into X-rays. This is a fundamental step in understanding the physical mechanisms within the jets produced by supermassive black holes. IXPE is the only satellite capable of measuring X-ray polarization and uses detectors developed in Italy by INFN and INAF. The discovery, led by astrophysicist Iván Agudo of the Instituto de Astrofísica de Andalucía, solves one of the most discussed mysteries in modern astrophysics.