Scientists solve half-century-old mystery of X-rays from black holes 16:03

Finnish astrophysicists from the University of Helsinki have uncovered a secret that has intrigued their colleagues since the 1970s. They have figured out why black holes act as powerful sources of X-rays. The study was published in the scientific journal magazine Nature Communications (NatComms).

Most observed black holes have a companion star with which they form a binary star system. In a binary system, the objects orbit each other and the companion star’s material is gradually drawn into its gravitational funnel. This slow-moving stream of gas often forms an accretion disk around the black hole, a bright, observable source of X-ray radiation.

Scientists used detailed supercomputer simulations to simulate the interactions between radiation, plasma and magnetic fields around black holes. They found that the chaotic motions (turbulence) caused by the magnetic fields heat up the local plasma, causing it to emit X-rays.

In a simulated electron-positron plasma and photon mixture, local X-rays can be converted into electrons and positrons, which can then be converted back into radiation on contact.

Turbulent plasma naturally produces X-rays seen in accretion disks.

The simulations also made it possible to see for the first time that the plasma around black holes can exist in two different equilibrium states, depending on the external radiation field. In one case, the plasma is cold and transparent, and in the other, it is hot and impenetrable.

Earlier scientists solved It’s a long-standing mystery that supermassive black holes are merging in a way that defies the known laws of physics.