Active galaxies constitute a significant fraction of all galaxies. Their cores are much more luminous than the rest of the galaxy. This activity is interpreted as due to the presence of a supermassive black hole (with a mass ranging from several million to several billion solar masses) in the centre of the core and by the radiation produced by the accretion of matter surrounding this black hole.
In ordert to explain the diverse aspects of this activity, the unified model of active galactic cores postulates that a toroidal concentration of dust and gas with a radius ranging from several parsecs to several tens of parsecs surrounds the supermassive black hole and its accretion disc. The existence of this dense and opaque concentration of gas and dust has until now only been inferred indirectly.
During the summer of 2014, the exoplanet hunter SPHERE1 was installed at the VLT in Chile. To find new exoplanets, this instrument is has extremely efficient adaptive optics coupled to a variety of observational modes of operation. Using in particular the polarimetric mode, the team led by Damien Gratadour has obtained images of unprecedented quality of the active core of the galaxy NGC 1068. The spatial resolution, 2,5 pc, is nearly 20 times better than that obtained without the correcting system, thanks to which it has been possible to reveal specific structures within the active core : a double cone in the form of an hour glass, and an elongated central structure aligned in a direction perpendicular to the axis of the double cone.
The first structure highlights clearly the less dense region within which gas clouds are ionized by the intense radiation emerging from the central supermassive black hole. The second structure, extending over about 55 pc with a thickness of about 20 pc, is revealed by the light radiated by the central source and scattered by the dust in this torus. This is thus the first direct observation of the dust torus postulated by the unified model of active galactic cores
