Black holes, often perceived as cosmic vacuum cleaners, actually play a much more complex role in the Universe. They act as true energy engines, capable of redistributing enormous amounts of energy. This energy, extracted from their immediate surroundings through their rotation and powerful magnetic fields, powers jets of particles and influences the dynamics of galaxies.
Advanced computer simulations reveal that up to 70% of this energy can be redirected into space. These jets, composed of particles and radiation, erupt from the poles of black holes and play a crucial role in the surrounding regions. Researchers use 3D models to understand how magnetic fields interact with the rotation of black holes.
Illustration of an active quasar.
Credit: NASA, ESA, and CSA
Black holes are surrounded by accretion disks, structures of rotating gas and dust. When these disks are highly magnetized, they can extract some of the energy from the black hole's rotation through the Blandford-Znajek effect. This effect is considered the primary mechanism behind the formation of jets, although many questions remain about the distribution of this energy.
The simulations show that the efficiency of energy extraction depends on the black hole's rotation speed. The faster the black hole spins, the more energy it releases. However, some of this energy is absorbed by the disk or dissipated as heat, complicating the understanding of the processes at play.
Researchers have also observed that intense magnetic fields increase the brightness of the accretion disk. This additional brightness could explain why some black holes appear brighter than predicted by theoretical models. The unused energy near the black hole could also contribute to the formation of a corona, a region of hot gas emitting X-rays.
Future simulations aim to better understand the formation of jets and coronae around black holes. These studies could shed light on the energy mechanisms at work in the active nuclei of galaxies, such as quasars, and their impact on galaxy evolution.
What is the Blandford-Znajek effect?
The Blandford-Znajek effect is a physical process that allows the extraction of energy from a black hole's rotation. It occurs when intense magnetic fields interact with the accretion disk surrounding the black hole. This interaction generates jets of particles and radiation that escape from the black hole's poles.
This mechanism is crucial for understanding how black holes can influence their surroundings. The jets produced by the Blandford-Znajek effect are among the most energetic phenomena in the Universe. They can travel intergalactic distances and play a key role in galaxy formation.
How do simulations help us understand black holes?
Computer simulations are essential tools for studying black holes. They allow researchers to model the interactions between magnetic fields, accretion disks, and black hole rotation. These models incorporate the laws of general relativity and magnetohydrodynamics to replicate the extreme conditions near black holes.
Thanks to these simulations, researchers can explore scenarios that are impossible to observe directly. For example, they can study how energy is extracted and redistributed around black holes. These studies provide valuable insights into the formation of jets and coronae, as well as their impact on galaxies.