An article published in “The Astrophysical Journal Letters” reports the results of a study on the region of very hot plasma that surrounds a black hole called the corona. A group of researchers used detections conducted with the IXPE space telescope to obtain precise information on the corona of 12 black holes ranging from stellar-mass ones to supermassive black holes. For the first time, it was possible to observe the geometry of the corona of black holes and its relationship with the accretion disk that surrounds them. The geometry seems very similar regardless of the size of the black holes but this is still a tentative result.
Astronomers have been able to observe the details of accretion disks around black holes but were not so successful with the corona. To achieve this result, a polarimetric instrument such as IXPE (Imaging X-ray Polarimetry Explorer), a mission by NASA and the Italian Space Agency launched on December 9, 2021, was needed: it can detect the polarization of X-rays, allowing the structure and shape of the corona of black holes to be mapped.
Stars also have a corona of very hot plasma. The Sun’s corona has temperatures that can reach a million degrees Celsius, while it’s estimated that the plasma in the corona of black holes can reach temperatures of billions of degrees Celsius.
The detections conducted with the IXPE space telescope indicate that the corona extends in the same direction as the accretion disk of the black hole. This offers clues to its shape and proves the relationship with the accretion disk. Instead, the possibility that the corona has the shape of a lamppost hovering above the disk has been ruled out.
The observations included 12 black holes ranging from Cygnus X-1 and Cygnus X-3, binary systems with stellar-mass black holes, to the supermassive black holes at the center of the Circinus Galaxy and the galaxies NGC 1068 and NGC 4151.
The results suggest that the black holes created accretion disks and coronae with a similar geometry. This is surprising considering that stellar black holes can steal gas from a companion while supermassive black holes gobble up all the gas close enough.
The researchers hope to conduct further examinations of black holes of both types to verify these similarities. According to Lynnie Saade, a researcher at NASA’s Marshall Space Flight Center in Huntsville and lead author of this study, there’s still much more to be learned from X-ray studies of black holes, and the IXPE space telescope provided the first opportunity in a long time to reveal their accretion processes and unlock new findings about these extreme objects.