A black hole does not necessarily retain all the matter it attracts. In the Swift J1727.8−1613 system, a large amount of gas seems to be heading back out into space. According to the researchers, this outflow could be comparable to the amount absorbed at the same time.
This system consists of a black hole and a small star orbiting each other. The black hole has about ten times the mass of the Sun. It gradually pulls gas from its companion, forming a very hot disk around it.
Representation of the geometry of the system and its physical processes.
In August 2023, the system suddenly became very bright in X-rays. Astronomers followed this entire outburst with the Very Large Telescope, located in Chile. Its X-Shooter instrument split the incoming light in order to study the motions and properties of the gas.
During the most intense phase, the black hole produced a narrow jet of matter. The observations also show a change in the outer part of the disk. This outer part appears to have received more radiation, with no detectable change in the region closest to the black hole.
The surprise came when the outburst had largely subsided. Certain features observed in the light indicate that a gas wind continued to escape from the disk. This gas, relatively cold for such an environment, was moving at about 750 kilometers per second.
Simulations reproduced the shape of these features with a dense, rotating and accelerating wind. The researchers estimate that this wind was ejecting at least one billionth of a solar mass per year. This minimum rate would be comparable to the amount of matter absorbed by the black hole at the same time.
This comparison, however, remains an estimate. The result depends on the shape of the wind, its density and its physical state.