A lantern shines through thick fog. Light scatters off water droplets, and the lantern appears blurred. Something similar happens around a black hole: hot gas, like fog, envelops it, while X-rays from the inner parts of the disk struggle through this cloud. Only here, the "droplets" are electrons, and the "fog" itself is called the corona.
The authors of the new study built a model of such a corona for a black hole that is accreting matter very slowly — at about one-hundredth of the maximum possible rate. They considered not only light scattering off electrons but also pair production: when two photons collide with sufficient energy, they can transform into an electron and its antiparticle, a positron. This process, it turns out, significantly densifies the corona and squeezes it closer to the black hole.
The model allowed the team to compute how the X-ray emission would appear to an observer at different angles. It turns out that the degree of polarization (how much the light waves oscillate in a single plane) in the 2–8 keV range reaches 4–10%. These numbers agree well with data from real binary systems where a black hole pulls matter from a companion star. Such an "X-ray lantern" helps us peer into the very heart of an accreting black hole.
as written by the authors arXiv:2604.24961
We build a self-consistent model of a warm scattering corona near an accreting black hole in Kerr geometry, in the regime of slow ($$\sim 0.01$$ Eddington) mass accretion. An iterative Monte Carlo procedure is developed that incorporates self-consistently the effects of Compton scattering and electron-positron pair creation, as well as general relativistic lensing and frame dragging effects. Soft thermal photons are seeded in the inner disk and the velocity dispersion of the electrons and positrons adjusted to yield a fixed seed luminosity amplification through Compton scattering. A simple kinematic prescription is also added for bulk outflow. Pair creation by photon collisions raises significantly the density of scattering charges in and around the innermost ion disk, which is assumed to be geometrically thick and rarefied compared with the disk outside 10 gravitational radii. The self-consistent pair cloud is concentrated closer to the BH. The spectrum and polarization of the escaping X-rays are recorded as a function of the observer's orientation. The temperature and Compton parameter measured from the output spectra using the compPS package are consistent with fits to binary BH data in the hardest spectral state; the polarization degree rises to $$4-10\%$$ through the 2-8 keV band with allowance for $$e^\pm$$ upflow from the BH equator.
Electron-positron pairs in a black hole's corona are born from pure energy — two photons collide and vanish, and in their place appear two particles with mass. This is a direct example of Einstein's E=mc² in action.
In Charles Stross's novel "Accelerando," civilizations are described that use black hole accretion disks as sources of energy and raw materials for producing antimatter — almost like in this model.