Two disks that rotate in opposite directions around the supermassive black hole at the center of the galaxy NGC 1068


An article published in the journal “The Astrophysical Journal” reports the discovery of a supermassive black hole at the center of the galaxy NGC 1068 surrounded by two gas disks that rotate in opposite directions. A team of researchers led by Caterina Maria Violette Impellizzeri of the National Radio Astronomy Observatory (NRAO) used the ALMA radio telescope to observe the center of that galaxy in sufficient detail to detect the two disks and their motions. That situation is not very stable and in the future a collision between the two rings could generate an abundant meal for the black hole. That’s a possible quick growth mechanism for supermassive black holes.

Observations made in the very deep space allowed to study very ancient galaxies, discovering that supermassive black holes already existed when the universe was “only” a billion years old. Various theories have been proposed to explain how objects with masses even billions of times the Sun’s were formed at the center of galaxies that at that time had formed recently. This new research proposes at least one possible quick growth mechanism for a supermassive black hole.

About 47 million light years away from Earth, the galaxy NGC 1068, also known as Messier 77 or simply as M 77, is visible even with small telescopes. It has an active galactic nucleus powered by a supermassive black hole surrounded by a considerable amount of materials it heats up to the point that they emit strong electromagnetic radiation. However, the amount of dust in that area is considerable and filters visible light so those emissions must be studied with instruments capable of detecting the electromagnetic wavelengths that pass through that dust.

A research published in the magazine “Monthly Notices of the Royal Astronomical Society letters” in December 2015 described a research on the supermassive black hole at the center of the galaxy NGC 1068 which among other things noted that the structure of the disk around it isn’t homogeneous. In that case, ESA’s XMM-Newton and NASA’ NuSTAR space telescopes detected the X-rays emitted by those materials. In this new research, the power and sensitivity of the ALMA radio telescope were exploited to detect the radio waves emitted by those materials obtaining very interesting and surprising results.

The details of the nucleus of the galaxy NGC 1068 detected by the ALMA radio telescope (Atacama Large Millimeter/submillimeter Array), inaugurated in March 2013, showed that around its supermassive black hole there’s an inner disk between 2 and 4 light years which rotates in the same direction as the galaxy, and a second outer disk between 4 and 22 light-years that rotates in the opposite direction.

The image above (ALMA (ESO/NAOJ/NRAO), V. Impellizzeri; NRAO/AUI/NSF, S. Dagnello) shows an ALMA image that illustrates the situation in the nucleus of the galaxy NGC 1068. The colors indicate the motion of the gas: in blue the materials that are moving towards us, in red those that are moving away from us. The white triangles were added to show the accelerated gas expelled from the inner disk.

The presence of two disks with opposite motions is not normal but there are examples of that type in space. In general, such a situation is the consequence of an interaction between galaxies, in this case occurred in the distant past.

The situation is stable only for the moment but in the future the materials of the outer disk will approach the internal disk until they collide. At that point, there could be a collapse of both, and the materials will end up in the supermassive black hole. It could be one of the mechanisms that allows these objects to grow considerably and this makes this research even more interesting. An instrument like the ALMA radio telescope could allow to find other similar situations to verify this hypothesis.

Artist's concept of the disks around the supermassive black hole at the center of the galaxy NGC 1068 (Image NRAO/AUI/NSF, S. Dagnello)
Artist’s concept of the disks around the supermassive black hole at the center of the galaxy NGC 1068 (Image NRAO/AUI/NSF, S. Dagnello)

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