The Galactic centre: a remarkable astrophysical system
Abstract: I will give an introduction to the structure and dynamics of the Galactic centre. This region hosts a complex star-forming ecosystem that is continually exchanging matter with the rest of the Galaxy through inflows and outflows. The Galactic bar efficiently transports gas from the Galactic disc inwards at a typical rate of ~1 Msun/yr, creating a ring-like accumulation of molecular gas known as the Central Molecular Zone (CMZ) at a radius R=120pc. The CMZ forms by a process similar to the one responsible for creating gaps in Saturn’s rings, and is the local analog of the star-forming nuclear rings commonly found at the centre of external barred galaxies. Once in the ring, approximately 10% of the gas is consumed by its intense star formation activity. Star formation does not occur uniformly throughout the CMZ ring, but is more likely to occur near the sites where the bar-driven gas inflow is deposited. The star formation rate of the CMZ varies as a function of time, but it is currently debated whether this is due to an internal feedback cycle or to external variation in the bar-driven inflow rate. The radius of the CMZ gas ring slowly grows over secular timescales (Gyr), and its star formation activity builds up a flattened stellar system known as the nuclear stellar disc, which currently dominates the gravitational potential of the Milky Way at Galactocentric radii 30pc<R<300pc. Most of the gas not consumed by star formation in the CMZ is ejected perpendicularly to the plane by a Galactic outflow powered either by stellar feedback and/or the central black hole’s activity, while a tiny fraction continues moving radially inward, probably in an intermittent fashion, towards the circum-nuclear disc at R=few pc, and eventually into the sphere of influence of the central massive black hole SgrA* at R<1pc.
Aula U2-2016