Previewing a common relativistic plasma simulation without collision. Researchers have used one of the world's most powerful supercomputers to better understand how high energy plasma jets evade the intense gravity of a black hole that absorbs everything else along its path – including light.
Before stars and other matter cross a point without returning a black hole – a limit known as the "horizon of events" – and consumed by the black hole, they are erased in the rotation of the black hole. An issue that has been worrying physicists for decades is how some energy manages to escape from the process and focus on plasma streams that pass through the space near the speed of light.
As described in an article published last week in Exploration of Letters researchers linked to the Department of Energy and the University of California at Berkeley used a supercomputer at Lawrence Berkeley National Laboratory to simulate plasma jets, electrically charged gaseous substance.
Simulations ultimately reconcile two decades of old theories that try to explain how energy can be extracted from a rotating black hole.
The first theory describes how electric currents around a black hole twist the magnetic field to create a jet known as the Blandford-Znajek mechanism. This theory suggests that the material captured in the gravity of a rotating black hole will become more magnetized as soon as it reaches the horizon of events. The black hole acts as a massive wire rotate in a huge magnetic field, which will cause an energy difference between the poles of the black hole and the equator. This energy difference is then dissipated as jets at the poles of the black hole.
The other theory describes the Penrose process, in which particles approaching the horizon of black hole events separate. In this scenario, half of the particle is fired from the black hole and the other half of the particle carries negative energy and falls into the black hole.
"There is an area around a rotating black hole called the ergosphere inside of which all the particles are forced to rotate in the same direction as the black hole," Kyle Parfry, the lead author of the paper and a theoretical astrophysicist at NASA, told me in email. "In this region, it is possible for a particle to effectively have negative energy in some sense if it tries to move in orbit against the rotation of the hole."
In other words, if half of the particle is scattered against a black hole spina, it will reduce the angular momentum or rotation of the black hole. But this rotational energy has to go somewhere. In this case, it becomes an energy that pushes the other half of the black hole particle. According to Parfrey, the Penrose process observed in their simulations is slightly different from the classical particle separation situation described above. Instead of partial separation, the charged particles in the plasma are affected by electromagnetic forces, some of which are propelled against the black hole rotation in a negative energy trajectory. In that sense, Parfrey told me they were still considered Penrose.
Read more: Astronomers discover a supermassive black hole that rotates half the speed of light
The surprising part of the simulation, Parfrey told me, was that it establishes a link between the Penford process and the mechanism of Blandford-Znajek, which has never been seen before.
In order to create twisting magnetic fields that extract energy from the black hole in the Blandford-Stroke mechanism, the electric current carried by particles within the plasma and a significant number of these particles has the negative energy characteristic of the Penrose process.
"It seems that at least in some cases the two mechanisms are linked," said Parfrey.
Parfrey and his colleagues hope their models will provide the required context for photos from the Event Horizon telescope, an array of telescopes designed to directly portray the horizon of the events where these plasma jets are formed. Until the first image was produced, Parferi said he and his colleagues wanted to improve these simulations so they could adapt even better to existing observations.