4 research outputs found
Simple hydrodynamical Simulations of the Circumnuclear Disk
The âcircumnuclear diskâ (CND) is a dense, clumpy, asymmetric ringâlike feature centered on Sgr A*. The outer edge of the CND is not distinct but the disk extends for more than 7 pc; the distinct inner edge, at a radius of â1.5 pc, surrounds the âminiâspiralâ of the HII region, Sgr A West. We present simple 3D hydrodynamical models of the formation and evolution of the CND from multiple selfgravitating infalling clouds and compare the results with recent observations. We assume the clouds are initially BonnerâEbert spheres, in equilibrium with a hot confining interâcloud medium. We include the gravitational potential due to the pointâmass of Sgr A* as well as the extended mass distribution of the underlying stellar population. We also include the effects of the ram pressure due to the stellar winds from the central cluster of earlyâtype stars.
A single spherically symmetric cloud cannot reproduce the clumpy morphology of the CND; multiple clouds on diverse trajectories are required so that cloudâcloud collisions can circularize the clouds' orbits while maintaining a clumpy morphology. Collisions also serve to compress the clouds, delaying tidal disruption while potentially hastening gravitational collapse. Low density clumps are disrupted before reaching the inner CND radius, forming shortâlived arcs. The outer parts of more massive clumps get tidally stripped, forming longâlived lowâdensity wideâangle arcs, while their cores potentially undergo gravitational collapse. The fine balance between resisting tidal disruption and preventing gravitational collapse implies that most if not all clumps are not stable for much more than an orbit. Thus, in order for the CND to be a longâlived clumpy object, it must be continually fed by additional inâfalling clouds. Clouds that survive to small radii are likely to be the sites of present or future star formation. However, within a few parsecs of Sgr A*, the stellar winds decelerate any inâfalling cloud so that the windâcloud interface becomes RayleighâTaylor unstable, potentially disrupting the cloud and inhibiting star formation