Recent advancements in astrophysics have led to groundbreaking observations of the gas flows surrounding supermassive black holes. These observations, conducted at a remarkably detailed light-year scale, have revealed crucial insights into the behavior of these cosmic giants. Notably, researchers have discovered that while a significant amount of gas is drawn towards these black holes, only a small fraction – about 3 percent – is actually consumed. The rest of the gas is ejected and then recycled back into the host galaxy.
Not all of the matter which falls towards a black hole is absorbed, some of it is ejected as outflows. But the ratio of the matter that the black hole “eats,” and the amount “dropped” has been difficult to measure.
An international research team led by Takuma Izumi, an assistant professor at the National Astronomical Observatory of Japan, used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the supermassive black hole in the Circinus Galaxy, located 14 million light-years away in the direction of the constellation Circinus. This black hole is known to be actively feeding.
ALMA’s Role in Unveiling Black Hole Mysteries
Thanks to ALMA’s high resolution, the team was the first in the world to measure the amount of inflow and outflow down to a scale of a few light-years around the black hole. By measuring the flows of gasses in different states (molecular, atomic, and plasma) the team was able to determine the overall efficiency of black hole feeding and found that it was only about 3 percent. The team also confirmed that gravitational instability is driving the inflow.
Analysis also showed that the bulk of the expelled outflows are not fast enough to escape the galaxy and be lost. They are recycled back into the circumnuclear regions around the black hole, and start to slowly fall towards the black hole again.
Reference: “Supermassive black hole feeding and feedback observed on subparsec scales” by Takuma Izumi, Keiichi Wada, Masatoshi Imanishi, Kouichiro Nakanishi, Kotaro Kohno, Yuki Kudoh, Taiki Kawamuro, Shunsuke Baba, Naoki Matsumoto, Yutaka Fujita and Konrad R. W. Tristram, 2 November 2023, Science.
The study was funded by the National Astronomical Observatory of Japan and the Japan Society for the Promotion of Science.