Not everything that gets close to a black hole ends up in the belly of the beast. Before material crosses the point of no return – the event horizon – it has the chance to be thrown away in powerful jets of plasma. New simulations have now given scientists new insights on how those jets form.
As reported in Physical Review Letters, the simulations are based on a combination of plasma physics and general relativity. Their results reveal the mechanism that drives the electrical currents flowing around black holes and their interaction with the magnetic field, as well as another phenomenon known as the Penrose process. In this process, particles that cross the event horizon appear to have “negative energy” to a far-away observer.
In the model, the team has a collisionless plasma moving around the strong gravitational field of a virtual black hole. The simulations are obviously a simplification of real objects and they are basic compared to actual observations but they provide a new approach to understanding the nature and formation of the jets and how black holes power the jets of material, which in some cases can extend outward for millions of light-years.
“How can the energy in a black hole’s rotation be extracted to make jets?” lead author Dr Kyle Parfrey, from the Nuclear Science Division at Berkeley Lab, said in a statement. “This has been a question for a long time.”
The main culprit has been considered the Blandford-Znajek mechanism. The electric currents around a black hole twist the magnetic field into forming jets, “stealing” energy from the black hole by slowing down its rotation.
This visualization of a general-relativistic collisionless plasma simulation shows the density of positrons near the event horizon of a rotating black hole. Plasma instabilities produce island-like structures in the region of intense electric current. Kyle Parfrey et al./Berkeley Lab
The Penrose process is similar but it has to do with particles being eaten by the black hole, and for this reason, the black hole loses mass. This may seem like some sort of magic cake that you can eat and it makes you lose weight, but it has to do with specific configurations of matter. The idea is that a lump of matter moves around a black hole in a special orbit. Suddenly it breaks in two, with one part falling beyond the event horizon and the rest getting a boost (stealing energy) and escaping to infinity (and maybe beyond).
The team intends to improve on the model by including matter-antimatter pair creations and to have a more realistic radiation emission. The approach will hopefully tell us a lot more about what’s going on around these incredible objects.