Supermassive black holes are known to contain strong X-rays, UV photons and fierce space winds, all combining to create a formidable amount of energy. But could there be a calm zone surrounding these whirling collections of stars and space material? Researchers using the Atacama Large Millimeter/submillimeter Array (ALMA) think there is, based on their recent observations of a black hole near the center of NGC 1068, known as M77 to amateur stargazers.
Scientists theorized that these complex carbon-based molecules would be easily destroyed by the strong waves and radiation that surround the supermassive black holes. The new ALMA data tells a different story however, suggesting that pockets of calm exist even in this high-energy region. Astronomers have long been studying the molecular signatures around supermassive black holes: both the starburst regions and the surrounding rings of dust and gas known as a circumnuclear disks (CND) that spiral inward to feed an active black hole. These regions are important for understanding the evolution of galaxies, but can often be hard to observe.
A research team -- led by Shuro Takano at the National Astronomical Observatory of Japan (NAOJ) and Taku Nakajima at Nagoya University -- observed the spiral galaxy M77, which is located about 47 million light-years from Earth in the direction of the constellation Cetus (the Whale). Their findings were published in the journal Publications of the Astronomical Society of Japan in February 2015. This galaxy is known to have an actively feeding central black hole, which indicates it has a substantial circumnuclear disk. That disk, in turn, is surrounded by a 3,500 light-year wide starburst ring. ALMA is extremely sensitive and can produce high-fidelity images. Combined with earlier observations conducted by the 45-meter radio telescope at the Nobeyama Radio Observatory of the National Astronomical Observatory of Japan (NAOJ) Takano's team was able to reveal the distributions of nine types of molecules in the surrounding disk and starburst ring.
"In this observation, we used only 16 antennas, which are about one-fourth of the complete number of ALMA antennas, but it was really surprising that we could get so many molecular distribution maps in less than two hours. We have never obtained such a quantity of maps in one observation," said Takano.
The results clearly show that the molecular distribution varies according to the type of molecule. While carbon monoxide (CO) is distributed mainly in the starburst ring, five other types of molecules are concentrated primarily in the CND. In addition, carbon monosulfide (CS) and methanol (CH3OH) are distributed both in the starburst ring and the CND.
It was thought that a supermassive black hole would destroy complex organic molecules that surround it because as a black hole creates energy temperatures rise to extreme levels and intense X-rays and UV photos are emitted which would destroy the atomic bonds in these molecules. The ALMA observations, however, proved the contrary: Complex organic molecules are abundant in the CND, though not so in the broader starburst region.
"It was quite unexpected that complex molecules with a large number of atoms like acetonitrile and cyanoacetylene are concentrated around the black hole's disk," said Nakajima.
The research team speculates that organic molecules remain intact in the CND due to the large amount of gas there, which acts as a barrier for the X-rays and UV photons. Gas concentrations are lower in the starburst region so there are not as many organic molecules found there. The researchers point out that these results are a significant first step in understanding the structure, temperature, and density of gas surrounding the active black hole in M77.
