The torus around a supermassive black hole, observed for the first time

Using the ALMA (Atacama Large Millimeter-Submillimeter Array) array, a team of researchers, led by Santiago García-Burillo (of the National Astronomical Observatory (OAN-IGN), Spain) has managed to observe, for the first time, the dust and gas torus surrounding a supermassive black hole, in this case the one at the center of galaxy NGC 1068 (also known as Messier 77).

The core of galaxy NGC 1068.

Active Galactic Nuclei (AGN) galaxies are those that harbor a supermassive black hole at their core with signs of recent activity. These types of black holes accrete material while emitting a large amount of energy over a wide spectrum of wavelengths. It is believed that all galaxies, at some point in their lives, can be active galaxies.

For a period of activity to be triggered, the central supermassive black hole must be “fed” and, for a long time, it has been postulated that the fuel should be stored on a dust and gas disc surrounding the black hole. Although the immediate environment of the black holes of active galaxies may be as bright as the entire galaxy that houses it, some of these nuclei appear to be hidden behind a ring-shaped structure of dust and gas, called a “torus”.

The torus (or doughnut) shape, adopted in many theoretical models, would explain many of the enigmatic and spectacular features observed in active galaxies. But, due to the great distance that separates us from these objects, to isolate that small structure we need advanced instrumentation and the use of interferometric techniques, capable of achieving a very high angular resolution [1].  This has finally been made possible by the ALMA (Atacama Large Millimeter/submillimeter Array) antenna array.  

This is the first time that a circumnuclear disc of this type -its composition, dust emission, gas distribution and even its movement- is clearly observed [2].

NGC 1068 or Messier 77

This galaxy is one of the most active and, at the same time, one of the closest to us (it is about 50 million light years away), so, for decades, it has been the subject of numerous observational studies that have tried to detect the presence of that disc of torus-shaped material at its center, surrounding the supermassive black hole.

For Santiago García-Burillo, astrophysicist at the National Astronomical Observatory (OAN-IGN), member of ASTROMOL and principal investigator of this work, “These observations are an evidence of what ALMA can do, managing to spatially detect and solve very small structures in nearby galaxies. We will be able to know more about the behavior of these discs and how they stabilize around the supermassive black holes, feeding them to create monsters whose mass can reach from millions to billions of times the mass of our Sun.”

These observations demonstrate the existence of these discs. However, the torus discovered in NGC1068 appears to be much more complex than expected. The next step will be to study other similar galaxies to see if this uncovered complexity is a common phenomenon in galaxies with active nuclei or whether, on the contrary, NGC 1068 is an exception.


[1] Better than 0.1″ (arcseconds).

2] The emission in the continuum of dust from the torus has been obtained, but, most notably, the torus has also been spatially resolved in the emission of molecular gas. To do this, the 6-5 rotational line of carbon monoxide (CO) was used as a dense gas tracer (n(H2)~1×105 cm-3). This allowed to derive the size of the torus (about 7-10 pc ~ 26 light-years in diameter) and study the kinematics of the gas, which turns out to be very complex: the gas would be expected to rotate regularly at these distances around the black hole, however, in addition to the gas disc appears to be praised, the gas has strong non-circular movements superimposed on rotation.

More information:

Paper: ALMA resolves the torus of NGC 1068: continuum and molecular line emission.

Other links:

NewScientist: Dusty doughnut around massive black hole spied for first time (Shannon Hall).


Image 1: The NASA/ESA Hubble Space Telescope has captured this vivid image of spiral galaxy Messier 77 — a galaxy in the constellation of Cetus, some 45 million light-years away from us. The streaks of red and blue in the image highlight pockets of star formation along the pinwheeling arms, with dark dust lanes stretching across the galaxy’s starry centre. The galaxy belongs to a class of galaxies known as Seyfert galaxies, which have highly ionised gas surrounding an intensely active centre. Credit: NASA/JPL-Caltech. Link to the original image.

Image 2: Emission on the continuum of the dust captured by ALMA on the circumnuclear disc of NGC1068 from scales of ~200 parsec ~ 600 light-years (panel-a) to the scales of the torus ~7-10 parsecs ~ 26 light-years (panels b and c).

Image 3: Emission (a) and speed field (b) of molecular gas detected by ALMA on the circumnuclear disc of NGC1068.