2026/04/06 by Shravan Vengalil Menon, Kun Hu, Henric Krawczynski
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #Black hole (networking) #Earth Systems and Cosmic Evolution #Hawking radiation #Reflection (computer programming) #Relativity and Gravitational Theory #Scattering #Sonic black hole #Spectral signature #Spinning #Spins #Strong gravity
paper · pdf · open access · doi:10.3847/2041-8213/ae6810
published in The Astrophysical Journal Letters 1003(1), L12 (IOP Publishing)
openalex publication_date 2026/05/18 · openalex created_date 2026/05/19 · openalex updated_date 2026/08/05
Abstract The Penrose process and the collisional Penrose process involve particles decaying or interacting very close to a spinning black hole, respectively, during which some particles are pushed into negative energy trajectories and fall into the black hole, while others gain that energy and escape the system. These two processes are difficult to observe as they occur very rarely by chance. Here we report a new observational signature of similar, but less extreme, processes occurring in and near the ergospheres of rapidly spinning black holes. We find that the reflection of the thermal emission from a geometrically thin optically thick accretion disk can lead to the formation of a power-law component, even in the absence of a corona. Unlike the well-known Penrose processes, the scattering particles lose a good fraction of their energy, but are not pushed into negative energy trajectories. We emphasize that this new component has distinct spectral and polarimetric properties that can be used for its identification as long as it outcompetes other power-law emission components. We emphasize that the new component needs to be taken into account when interpreting spectral and spectropolarimetric observations of black holes. The detection and unambiguous identification of the new component with current or future broadband X-ray spectral and spectropolarimetric missions can open a new window into testing Einstein’s theory of gravity close to the edges of black holes, and opens up new opportunities to constrain black hole spins and inclinations.