Gases Around Black Holes Are More Like Fountains Than Donuts

ALMA image of the gas around the supermassive black hole in the center of the Circinus Galaxy. The distributions of CO molecular gas and C atomic gas are shown in orange and cyan, respectively. ALMA (ESO/NAOJ/NRAO), Izumi et al.

At the center of almost every galaxy, there’s a supermassive black hole. These massive objects can be active if they have enough material to feed on. Astronomers tend to picture the gas falling into a black hole as a donut surrounding the extreme object, but a new analysis suggests a more dynamic interpretation.

The donut is not a rigid structure, but rather a consequence of certain interactions. The team described the system as a fountain in a city park, where the flow of material in and out creates complex interactions. Cold gas approaches the black hole on the plane of rotation. As it gets closer, it’s heated up and its molecules are broken down. Some of these atoms and ions can fall into the black hole but others are thrown back out. Some of this escaping gas falls back onto the disk, forming the characteristic donut shape previously observed.

As reported in the Astrophysical Journal, the team used a combination of computer models and observations of a nearby supermassive black hole from the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA was able to track the cold and warm gas at the center of a galaxy known as Circinus, which is located 14 million light-years away. Being relatively close, it gave the researchers a unique perspective on the environment around black holes.

“By investigating the motion and distribution of both the cold molecular gas and warm atomic gas with ALMA, we demonstrated the origin of the so-called ‘donut’ structure around active black holes,” said lead author Takuma Izumi, a researcher at the National Astronomical Observatory of Japan (NAOJ), in a statement. “Based on this discovery, we need to rewrite the astronomy textbooks.”

Artist’s impression of the gas' motion around the supermassive black hole in the center of the Circinus Galaxy. NAOJ

The team had access to a powerful supercomputer operated by the NAOJ, which allowed them to test the potential motion in the “donut” in a different way. They were then able to compare their simulations to the detailed observations made by ALMA. 

“Previous theoretical models set a priori assumptions of rigid donuts,” co-author Keiichi Wada, a theoretician at Kagoshima University in Japan, explained. “Rather than starting from assumptions, our simulation started from the physical equations and showed for the first time that the gas circulation naturally forms a donut. Our simulation can also explain various observational features of the system.”

This research brings forward more understanding of a very complex region of space, although there is still a lot for us to learn.

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