Astronomers have observed that black holes regulate the expulsion of matter by alternating between two distinct types of outflows: high-speed jets and broader X-ray winds, without producing both simultaneously. This discovery, based on a three-year study of a black hole system, enhances understanding of how black holes manage their energy output and interact with their cosmic environments, influencing processes like star formation and galaxy evolution.
Black Hole Outflows Defined
Material drawn into a black hole system typically forms an accretion disk, a swirling body of plasma, before either falling into the black hole or being expelled into space. Prior to this study, the precise mechanism regulating the expulsion of this matter and the relationship between different outflow types remained unclear.
Two primary forms of these outflows have been identified:
- Relativistic Jets: These are narrow beams of plasma projected from the black hole's poles, moving at speeds approaching that of light.
- X-ray Winds: These consist of broader streams of ionized gas that emanate from the surface of the accretion disk.
New Observational Findings
A study published in Nature Astronomy, led by researchers at the University of Warwick, presents observational evidence that these two types of outflows are mutually exclusive. When one outflow is active, the other is not, indicating a competitive process for the black hole's energy output. Dr. Jiachen Jiang, a lead author of the study, described this phenomenon as an "energetic tug-of-war" within the black hole's accretion flow.
The research focused on the black hole system 4U 1630−472, which has a mass approximately ten times that of our Sun and actively draws matter from a companion star. Researchers utilized data collected over three years from NASA's Neutron star Interior Composition Explorer (NICER) X-ray telescope and South Africa's MeerKAT radio telescope.
Observations revealed that 4U 1630−472 never produced strong winds and strong jets simultaneously, even when the inflow of material to its accretion disk remained consistent. Zuobin Zhang of the University of Oxford noted that these observations provide evidence of black hole binary systems switching between these two powerful outflow modes.
Regulation Mechanism and Implications
This alternating behavior suggests a self-regulating mechanism where jets and winds compete for the same supply of mass or energy. Despite the changes in the form of the outflow, the total amount of mass and energy carried away remained comparable, indicating a consistent overall outflow rate from the black hole system.
The findings challenge prior assumptions that the switching between outflow types is solely driven by variations in the accretion rate—the amount of matter falling into the black hole. Instead, researchers theorize that the configuration of magnetic fields within the accretion disk may play a significant role in this regulatory process.
These outflows are considered crucial because they not only remove matter from the vicinity of black holes but also return this matter to the surrounding cosmic environment. Since gas and dust are essential for the formation of new stars, this mechanism of black hole energy output can influence star formation rates and, consequently, the evolution and growth of galaxies.