Scientists modeled the merger of a black hole and a neutron star

Using a supercomputer, a team of researchers from the Institute of Gravitational Physics of the Max Planck Society and Japan for the first time completely modeled the collision of a black hole and a neutron star. In their work, they calculated the state of the system at the final stages of orbital rendezvous, during the merger, as well as at the subsequent stage when, according to available data, a gamma-ray burst may occur.

Merging of a black hole and a neutron star

The researchers studied two scenarios. In one, a rotating black hole with a mass of 5.4 solar participated in the merger, in the other its mass was 8.1 solar. The mass of the neutron star in all scenarios exceeded the mass of our Sun by 1.35 times. These parameters were chosen based on the assumption that the neutron star would be torn apart by tidal forces from the black hole. 

Merging of a black hole and a neutron star in the artist’s Image.  Source: Carl Knox/OzGrav ARC Centre of Excellence

According to the researchers, although the whole process lasts about two seconds, an extremely large number of events occur during this period of time. The neutron star completes its last orbits, after which its destruction occurs under the action of tidal forces, the ejection of matter, the formation of an accretion disk and jets.

Gamma flash and gold

Modeling has shown that about 80% of the matter of a neutron star (about one solar mass) is absorbed by a black hole within a few milliseconds. During the next 10 milliseconds, the remaining matter of the neutron star forms a one-arm spiral structure.

In the future, some matter from the spiral arm is ejected from the system, while the remaining part forms an accretion disk around the black hole. When this accretion disk falls on a black hole, it leads to the formation of a jet of electromagnetic radiation capable of producing a short gamma-ray flash. The study also showed that heavy elements such as gold and platinum may be present in the flows of the erupted material.

It is worth noting that it took about two months for the Sakura supercomputer to recreate the two-second event. That is why, in such cases, scientists often limit themselves to modeling very short processes. However, the team of researchers believes that only end-to-end simulation can give a self-consistent picture of all processes. It has already started work, the purpose of which is to simulate the merger of two neutron stars.

You can also read about how the “space police” discovered a sleeping black hole in a neighboring galaxy.

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