On December 20, 2024, a team of astrophysicists from the Czech Academy of Sciences announced significant advancements in understanding black hole behavior through two international studies focusing on X-ray binary systems.
The studies center on Swift J1727.8-1613, a black hole binary system that became visible in August 2023, attracting global attention for its brightness in X-ray wavelengths. This system exhibited a sudden flare, typical of binary systems, but notably brighter than the Crab Nebula, a well-known X-ray source in our galaxy.
Observations utilized the IXPE satellite, a collaboration between NASA and the Italian Space Agency, equipped with a specialized telescope for measuring X-ray polarization. Polarization reveals the orientation of light waves, providing insights into the processes occurring near black holes, where strong gravity influences surrounding material and radiation.
The first study, led by Jiří Svoboda, examined dramatic changes in X-ray polarization during various phases of Swift J1727.8-1613's outburst from August 2023 to February 2024. The research revealed significant polarization changes during the transition between hard and soft spectral states of X-ray radiation, indicating alterations in the structure of the accretion disk and corona surrounding the black hole.
The second study, directed by Jakub Podgorný, focused on the restoration of X-ray polarization after the system returned to a hard state in April 2024. This state, characterized by higher energy radiation, showed a return of polarization levels similar to those observed in the initial outburst, suggesting stability in the corona's geometry despite a significant decrease in brightness.
These findings mark a substantial step forward in understanding black hole interactions with surrounding material, demonstrating that X-ray polarization analysis is a vital tool for studying these phenomena. Further observations with IXPE are necessary to fully determine configurations around black holes in binary systems, as emphasized by Michal Dovčiak, a key contributor to the studies.