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Sgr A* is extra-ordinarily dim in all wavelengths requiring a very low accretion rate at the present time. However, at a radial distance of a fraction of a parsec from Sgr A*, two rings populated by young massive stars suggest a recent burst of star formation in a rather hostile environment. Here we explore two ways of creating such young stellar rings with a gaseous accretion disk: by self-gravity in a massive disk, and by capturing old low mass stars and growing them via gas accretion in a disk. The minimum disk mass is above 10^4 Msun for the first mechanism and is few tens times larger for the second one. The observed relatively small velocity dispersion of the stars rules out disks more massive than around 10^5 Msun: heavier stellar or gas disks would warp each other by orbital precession in an axisymmetric potential too strongly. The capture of old stars by a disk is thus unlikely as the origin of the young stellar disks. The absence of a massive nuclear gas disk in Sgr A* now implies that the disk was either accreted by the SMBH, which would then imply almost a quasar-like luminosity for Sgr A*, or was consumed in the star formation episode. The latter possibility appears to be more likely on theoretical grounds. We also consider whether accretion disk plane changes, expected to occur due to fluctuations in the angular momentum of gas infalling into the central parsec of a galaxy, would dislodge the embedded stars from the disk midplane. We find that the stars leave the disk midplane only if the disk orientation changes on time scales much shorter than the disk viscous time.
A linear stability analysis has been performed onto a self-gravitating magnetized gas disk bounded by external pressure. The resulting dispersion relation is fully explained by three kinds of instability: a Parker-type instability driven by self-grav
Submillimeter bright galaxies in the early Universe are vigorously forming stars at ~1000 times higher rate than the Milky Way. A large fraction of stars is formed in the central 1 kiloparsec region, that is comparable in size to massive, quiescent g
A self-similar solution for time evolution of isothermal, self-gravitating viscous disks is found under the condition that $alpha equiv alpha (H/r)$ is constant in space (where $alpha$ is the viscosity parameter and $H/r$ is the ratio of a half-thick
We report new infrared measurements of the supermassive black hole at the Galactic Center, Sgr A*, over a decade that was previously inaccessible at these wavelengths. This enables a variability study that addresses variability timescales that are te
We investigate the tidal interaction between a low-mass planet and a self-gravitating protoplanetary disk, by means of two-dimensional hydrodynamic simulations. We first show that considering a planet freely migrating in a disk without self-gravity l