On March 24, 2021 the scientific collaboration Event Horizon Telescope (EHT), which in 2019 had published the first "photo" of a black hole, published a fantastic new representation of the huge astrophysical object (the size of our solar system, but of mass billions of times that of the Sun!) at the center of the active galaxy M87: it is the image in polarized light in the radio band, which for the first time directly shows us the structure of the magnetic field around the accretion black hole.

From this study, valuable information is obtained to understand the behavior of magnetic fields around black holes and the processes that, in these extremely dense and energetic regions, are able to accelerate particle jets at highly relativistic speeds so powerful that they extend far beyond the M87 galaxy itself.

The luminous jets of energy and matter, which come out of the core of M87 and extend for thousands of light years from its center, are one of the most mysterious and energetic phenomena in the galaxy. Most of the matter that is near the edge of a black hole falls into it. However, some of the particles manage to escape shortly before being captured, and are thus accelerated into space in the form of jets.

This new polarized light image is based on the same data collected in 2017, but it took years of work for the EHT collaboration to develop complex data analysis techniques and validate them through simulations. The polarized light image now provides fundamental additional information on what produces the emission that the original 2019 image could not provide and also allowed to estimate the density and temperature of the rotating plasma at small distances to the black hole.