Ranjeev Misra

For years, an X-ray telescope in orbit recorded how binary systems shine, where an ordinary star orbits a black hole or a neutron star. Matter from the companion falls onto the compact object, heats up to millions of degrees, and emits X-rays.

At the center of the galaxy Ton S180 lurks a black hole that occasionally flares in X-rays. These flares are like a flashlight beam shining onto a swirling disk of superheated gas. Part of the light heads straight toward us, while another part first hits the disk, bounces off, and only then reaches the telescope.

During its 2021 outburst, the black hole in the GX 339-4 system behaved like an actress changing costumes between scenes. In the hard state, it wore two coronas at once: a hot, rarefied one, and over it, a warm, dense one. In the soft state, only the hot corona remained.