A supermassive black hole

It is holed up in gas trenches, particularly dense pockets of organic molecules that are resistant to lethal radiation that permeates the surroundings of the supermassive black hole in the process of power at the center of the galaxy M77. It was discovered by a research group of Japanese guidance using the radio telescope ALMA in Chile.


Credit: ESO/C. Malin

Using the array of radio telescope ALMA (Atacama Large Millimeter / submillimeter Array) in Chile, a group of astronomers has discovered pockets of organic molecules in the vicinity of the supermassive black hole at the center of the galaxy NGC 1068, better known to fans as M77, 47 million light-years away in the constellation of Cetus. Contrary to expectations, these clouds of organic molecules are not destroyed by the intense radiation – X-ray and ultraviolet – that usually permeate the environment surrounding the supermassive black holes.
According to the research team, led by Shuro Takano National Astronomical Observatory of Japan (NAOJ) along with Taku Nakajima of Nagoya University, it is as if the organic molecules were in the areas of relative calm near the eye of the storm, probably defended by a shield with particularly dense gas and dust that filters radiation otherwise lethal.
The interstellar gas contains a wide variety of molecules, differentiated according to the environment in which they are generated. For example, the hot star-forming regions produce different molecules than those commonly found in cold interstellar regions. This allows scientists to deduce the temperature and density of some galactic regions by studying their chemical composition. Of particular interest are the accretion discs, rings of falling matter spiral on the black hole to power it. These regions are important for understanding the evolution of galaxies, but observations are often difficult.
Thanks to the power of ALMA, the team Takano managed to capture the faint radio emission of the molecules present in M77. This galaxy is known to possess a central black hole that is feeding voraciously using a gargantuan circumnuclear disc. Disc which, in turn, is surrounded by an area with a ring of star formation that extends 3,500 light years. The new ALMA observations clearly showed the distribution of nine types of molecules in the accretion disk and the ring around it.


Credit: ALMA(ESO/NAOJ/NRAO), S. Takano et al., NASA/ESA Hubble Space Telescope and A. van der Hoeven

“In this observation, we have used only 16 antennas, which are about a quarter of the total number of antennas which is available on ALMA, but it was very surprising to obtain many maps of molecular distribution in less than two hours. We never got such a lot of maps in a single observation, “said Takano.
The results reveal that the molecular distribution varies depending on the type of molecule. Contrary to expectations, since their atomic bonds would be easily broken by UV radiation and X, the complex organic molecules are abundant in the accretion disk, but much less in the star-forming region surrounding.
It was quite unexpected to find that complex molecules with a large number of atoms, such as acetonitrile and cyanoacetylene, are concentrated around the accretion disk of the black hole,” said Nakajima.
The research group hypothesizes that organic molecules remain intact in the circumnuclear disk because of the large amount of gas present there, which acts as a barrier to X-rays and UV, while they could not survive the exposure to strong UV photons in the surrounding region star formation, in which the density of the gas is relatively low.
“ALMA projected astrochemistry in a new era,” commented Eric Herbst, the University of Virginia and a member of the research team. “Detecting and tracking the distribution of molecules throughout the cosmos allows us to know much more about areas otherwise hidden, just like the regions surrounding the black hole in M77.”

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