How can black holes merge

Computer simulations show for the first time how the jets of matter from supermassive black holes combine

Black hole

Toronto (Canada) / Baton Rouge (USA) - When black holes merge, the rays of matter emanating from them also merge. This leads to an outbreak of electromagnetic radiation that can be measured over billions of light years. This is shown by computer simulations presented by a trio of researchers from Canada and the USA in the current issue of the journal "Science". The simultaneous measurement of this typical electromagnetic radiation burst and gravitational waves could, the researchers say, prove to be a valuable astrophysical tool for studying dark energy or looking for deviations from general relativity.

The collisions and mergers of galaxies play an important role in the history of cosmic evolution. Most galaxies harbor supermassive black holes in their centers with a mass millions or even billions of times the mass of the sun. When galaxies merge, the central black holes inevitably approach each other, ultimately forming a double system and colliding in a final catastrophe.

In order to be able to predict the radiation signature of these processes, a precise understanding of the physical processes involved in the merging of black holes is necessary. In recent years, researchers have made great strides in this area, simulating, for example, the merging of black holes in a matter-free environment and the associated emission of gravitational waves. Carlos Palenzuela from the Canadian Institute for Theoretical Astrophysics (CITA) in Toronto, Luis Lehner from Louisiana State University in Baton Rouge and Steven Liebling from Long Island University in Brookville have now succeeded for the first time in detecting magnetic fields and thus also the rays of matter characteristic of black holes to include their simulations.

The computer simulation carried out by the three researchers shows that in the course of the merger, rays of matter form even with non-rotating black holes. In contrast to single black holes, in a double black hole these "jets" are not driven by the rotational energy, but by the kinetic energy of the orbital motion. In the further course, the jets of matter also unite and a "classic" rotating black hole is formed with jets at both poles. In addition to gravitational waves, a shower of electromagnetic radiation that can be measured from afar is also released.