Spiral arms, warping, and clumps formation in the Galactic center young stellar disk

TL;DR

This study uses advanced simulations to demonstrate that residual asphericity in the nuclear star cluster can naturally cause warping, spiral arm formation, and clumping in the Galactic center's young stellar disk, without requiring an intermediate-mass black hole.

Contribution

It shows that disk warping and clumping can result from intrinsic cluster asymmetries, challenging previous models that invoked intermediate-mass black holes.

Findings

Residual asphericity causes disk warping and spiral arms.

Spiral arms explain observed clumping and asymmetries.

Disk evolution is influenced by cluster structure and dynamics.

Abstract

The Galactic center of the Milky-Way harbors a massive black hole (BH) orbited by a diverse population of young and old stars. A significant fraction of the youngest stars ($\sim4-7$ Myr) reside in a thin stellar disk with puzzling properties; the disk appears to be warped, shows asymmetries, and contains one or more clumpy structures (e.g. IRS 13). Models explaining the clumping invoked the existence of an intermediate-mass BH of $10^{3}-10^{4}$ M$_{\odot}$, but no kinematic evidence for such a BH has been found. Here we use extended $N$-body simulations and hybrid self-consistent field method models to show that naturally formed residual temporal asphericity of the hosting nuclear star cluster gives rise to torques on the disk, which lead to changes in its orientation over time, and to recurrent formation and dissolution of single spiral arm ($m=1$ modes) structures. The changing orientation leads to a flapping-like behavior of the disk and to the formation of a warped disk structure. The spiral arms may explain the over-densities in the disk (clumping) and its observed asymmetry, without invoking the existence of an intermediate-mass BH. The spiral arms are also important for the overall disk evolution and can be used to constrain the structure and composition of the nuclear stellar cluster.