Located at a distance of about 45 million light-years in the southern constellation Fornax (the Furnace), NGC 1097 is a relatively bright, barred spiral galaxy seen face-on. The galaxy is a moderate example of an Active Galactic Nucleus (AGN), whose emission is thought to arise from matter (gas and stars) falling into oblivion in a central black hole. Astronomers have been trying to understand for a long time how the matter is "gulped" down towards the black hole. Watching directly the feeding process requires very high spatial resolution at the centre of galaxies.
Astronomers obtained images of NGC 1097 with the adaptive optics NACO instrument attached to Yepun, the fourth Unit Telescope of ESO's VLT in Chile. These new images probe with unprecedented detail the presence and extent of material in the very proximity of the nucleus. The resolution achieved with the images is about 0.15 arcsecond, corresponding to about 30 light-years across. For comparison, this is only 8 times the distance between the Sun and its nearest star, Proxima Centauri.
NGC 1097 has a very strong bar and a prominent star-forming ring inside it. Interior to the ring, a secondary bar crosses the nucleus almost perpendicular to the primary bar. The newly released NACO near-infrared images show in addition more than 300 star-forming regions, a factor four larger than previously known from Hubble Space Telescope images. These "HII regions" can be seen as white spots in the photo. At the centre of the ring, a moderate active nucleus is located. Details from the nucleus and its immediate surroundings are however outshone by the overwhelming stellar light of the galaxy seen as the bright diffuse emission all over the image.
The astronomers also note that the curling of the spiral pattern in the innermost 300 light-years seem indeed to confirm the presence of a super-massive black hole in the centre of NGC 1097. Such a black hole in the centre of a galaxy causes the nuclear spiral to wind up as it approaches the centre, while in its absence the spiral would be unwinding as it moves closer to the center.
Image Credit: NASA/ESO