Strong evidence suggests that supermassive black holes influence the chemistry of their host galaxies

Supermassive black holes (SMBHs) cannot be ignored. They can be billions of times more massive than the Sun, and as they actively consume stars and gas, they become luminescent active galactic nuclei (AGN). The galactic center is a busy place, with activity centered on the SMBH. The new study provides compelling evidence that, while going about their business, SMBHs alter the chemistry of their host galaxy. Astrophysicists know a lot about SMBHs and their powerful effects on their host galaxies. It appears that most large galaxies are anchored to an SMBH at their center. Nothing can escape their attractive attraction. Even light is powerless. SMBH is responsible for active galactic nuclei, emitting powerful energy at all wavelengths. The energy comes from the swirling torus of sucked matter that surrounds the SMBH before falling into the hole.

Researchers also know that SMBH generates black hole feedback. The centers of large galaxies contain lots of hot gas that is dense enough to cool over tens or even hundreds of millions of years. This means cold air is moving towards the center. This cooling flow is expected to lead to massive stellar explosions near the galactic center. But in general, this is not what astrophysicists see. Instead, it appears that the SMBH launches powerful jets of material into the surrounding gas, keeping it hot and preventing the flow from cooling and leading to vigorous star formation. This is the response of a black hole. These are just some of the ways that black holes change their environment.

New research shows how the SMBH changes the presence and distribution of chemicals in the host galaxy. The study is titled “Molecular abundance of the perinuclear region around the active galactic nucleus in NGC 1068, based on a 3 mm band imaging line survey with ALMA.” It is published in the Astrophysical Journal and the lead authors are Toshiki Saito of the National Astronomical Observatory of Japan and Taku Nakajima of Nagoya University. Dust and gas block our view of the centers of galaxies and require special observational skills to peer inside. The Atacama Large Millimeter/Submillimeter Array (ALMA) is a group of 66 powerful radio telescopes that work together to produce impressive observing power. Researchers used ALMA to map the presence of chemicals in spiral galaxy NGC 1068, also known as M77 or the Ink Galaxy. They also used new machine learning techniques and mapped the distribution of 23 separate molecules. The team focused on two parts of NGC 1068: the nuclear circular disk and the ring star. Starburst rings (SBRs) are a prominent feature in some galaxies where pressure waves from the core collide with gas causing abundant star formation. There may also be other causes behind stellar explosions, including galaxy mergers or gravitational interactions with other galaxies. NGC 1068 has a ring star and this galaxy is also known as a stellar galaxy. This image is from separate research and shows the structure of NGC 1068. The ring of stars lies between the two dark blue lines and contains many super star clusters (SSCs). SSC is brighter and heavier than other clusters. Image credit: Rico-Vallas et al. 2021 The circular nuclear disk (CND) is a ring of molecular gas orbiting the SMBH.

Astrophysicists aren’t certain how these structures form or if they’re stable or transient. But they can contain an enormous amount of material. The Milky Way’s black hole, Sgr A*, contains tens of thousands of solar masses. The CND is closer to the SMBH than the SBR. The researchers also identified two prominent knotty structures in NGC 1068 that they call the ‘E Knot’ and the ‘W knot,’ which are parts of the CND. This study figure illustrates the structure of NGC 1068. The left panel shows both CND and SBR. The right panel zooms in on the CND and active galactic nuclei, and also shows two nodes. Image credit: Nakajima et al. 2023. The researchers mapped the chemicals in the two areas and found different distributions of different chemicals. This figure is from a study comparing the column density of each molecule on (a) a 350 pc scale and (b) a 60 pc scale. The bar graphs are red, blue, green, and black for CND (or AGN), Node E, Node W, and SBR, respectively.

The order of molecules is arranged in descending order from left to right based on column density towards CND in (a) or AGN in (b). Image credit: Nakajima et al. 2023. NGC 1068’s SMBH emits powerful rays that appear to change chemical properties. Carbon monoxide (CO) is a common molecule in galaxies, and energetic jets appear to disrupt it. There are fewer at CND, which is much closer to SMBH than SBR. The team also discovered unexpected concentrations of hydrogen cyanide (HCN) in the CND, possibly the result of strong shocks that created higher temperatures. CND also contains a lot of H13CN, SiO and H13CO+. In contrast, CND contains less cyanide (CN) than the model predicts due to high radiation. Although strong AGN is much closer to CND, the team believes that mechanical forces have a stronger overall effect on chemistry than AGN’s X-rays. The researchers also measured the fractional content of different chemicals by comparing them to carbon monosulfide (CS). Astronomers use CS because it is one of the best monitors of dense gases. This study data shows partial abundance relative to CS at (a) the 350 pc scale and (b) the 60 pc scale. The ratios relative to unity, indicated by the bold dashed line, represent an improvement in molecular abundance compared to CS.

for shocks. Silicon is present in dust particles and when the particles are shocked, it combines with oxygen to form SiO. Shock waves in galaxies compress, heat and accelerate gases, causing drastic chemical changes. The shocks are what cause gas clouds to collapse into protostellar cores, which eventually become stars. The SMBH and the entire galactic center are difficult to observe. These ALMA observations provide a detailed overview of the region and its compositions, as well as the most abundant chemical species. But the issue is not just the presence or absence of specific chemicals.