In this Thesis, I tackle several open issues regarding the Galactic center (GC) and other galactic nuclei (GNs). First, I describe a novel scenario for the formation of the so-called circumnuclear ring (CNR), a clumpy torus of molecular gas which orbits at ∼2 pc from the supermassive black hole (SMBH) in the GC. Using smoothed-particle hydrodynamics (SPH) simulations, I show that the infall of a molecular cloud and its subsequent tidal disruption can form a clumpy ring whose properties match those of the CNR. An analogous tidal disruption episode has been proposed to explain the origin of the clockwise (CW) disk, the nearly-Keplerian disk of young (∼3Myr old) stars orbiting the SMBH in the GC. However, only 20-50% of the observed young stars lie in the CW disk, suggesting that some kind of perturbation had partially disrupted the disk in the past and produced the outliers. I investigate whether the source of such perturbation can be the CNR, by means of combined direct N-body and SPH simulations. I find that the CNR is not efficient in affecting the stellar disk on timescale consistent with the age of the young stars. On the other hand, I describe how gas in the inner cavity of the CNR could have played a substantial role in shaping the CW disk. The presence of gaseous rings is not a peculiarity of our Galaxy, but seems to be a rather common feature in GNs. Motivated by this, I performed the first systematic study on the formation of circumnuclear gas in GNs other than the GC. I simulate the infall of molecular clouds towards the center of several different GNs. All simulated GNs are modeled as a SMBH plus a nuclear star cluster (NSC), for which I considered a wide range of masses. I find that the morphology of circumnuclear gas can show distinct features depending on whether the gas settles inside or outside the SMBH influence radius. This suggests that the formation of CNR-like structures occurs only in the nuclear regions dominated by the gravity of the NSC. Finally, I investigated the origin of G2, a faint dusty object that has been observed to orbit the SMBH in the GC with a pericentre of only 133AU. Recent work indicates that G2 might be a starless planet brought into highly-eccentric orbit by some kind of mechanism. I investigate how the SMBH tidal field can strip planets from nearby stars, by means of high-accuracy few-body simulations and analytic models. I find that the orbit of planets escaped from the closest stars to the SMBH can match that of G2, except for its inclination. Future detection of stars with similar orbital plane as G2 in the central 1 00 of the GC will be able to further support this scenario.
|Titolo:||Dynamics in extreme environments: galactic nuclei|
|Data di pubblicazione:||20-ott-2017|
|Appare nelle tipologie:||8.1 PhD thesis|