Researchers at the University of Helsinki have successfully explained the X-ray radiation coming from the surroundings of black holes by using supercomputer simulations to model the interactions between radiation, plasma, and magnetic fields. The chaotic movements caused by the magnetic fields heat the local plasma and cause it to radiate, leading to the observed X-ray radiation from accretion disks around black holes. This research has been pursued since the 1970s and sheds light on the physics behind this phenomenon.
Black holes are formed when a large star collapses into a dense mass with gravity so strong that even light cannot escape. These black holes can only be observed indirectly through their effects on the surrounding environment. Most observed black holes are in binary star systems with a companion star, and as gas from the companion star spirals into the black hole, it forms an accretion disk that emits bright X-rays. Modeling the radiation from these accretion flows has been a challenge, but recent simulations have provided valuable insights into the process.
The simulations conducted by the researchers revealed that turbulence around black holes is so strong that even quantum effects become important for plasma dynamics. The interactions between electron-positron plasma and photons in the vicinity of black holes can lead to the conversion of X-ray radiation into particles that can then annihilate back into radiation. This phenomenon, where matter appears in place of bright light, is unique to the extreme environments around black holes and plays a crucial role in understanding the origins of X-ray radiation.
The study also showed that the plasma around black holes can exist in two distinct equilibrium states based on the external radiation field. In one state, the plasma is transparent and cold, while in the other, it becomes opaque and hot. This variation in states mirrors the observed changes between soft and hard states of X-ray radiation from black hole accretion disks. By incorporating quantum interactions between radiation and plasma, the researchers were able to create a more accurate model of the physics behind these phenomena.
The findings of this study, published in Nature Communications, provide a deeper understanding of the mechanisms behind X-ray radiation from black hole accretion disks. The research project, funded by a Starting Grant from the European Research Council, aims to unravel the complex interactions between plasma and radiation in extreme environments like those found around black holes. By incorporating all important quantum interactions in their simulations, the researchers have made significant progress toward explaining the origins of X-ray radiation from black hole surroundings.