Rich Kozai-Lidov Dynamics in an Initially Thin and Eccentric Stellar Disc Around a Supermassive Black Hole

TL;DR

This paper demonstrates that Kozai-Lidov oscillations can significantly alter the structure of eccentric stellar discs around supermassive black holes, especially in the presence of a spherical cluster, impacting star formation and disc evolution.

Contribution

It reveals the robustness of Kozai-Lidov oscillations in eccentric stellar discs and shows how a spherical cluster can trigger these oscillations, challenging previous damping assumptions.

Findings

Kozai-Lidov oscillations occur in eccentric stellar discs around SMBHs.

Presence of a spherical cluster can induce oscillations despite damping effects.

Oscillations can change disc thickness and eccentricity distribution.

Abstract

There is growing evidence of star formation in the vicinity of supermassive black holes (SMBH) in galactic nuclei. A viable scenario for this process assumes infall of a massive gas cloud towards the SMBH and subsequent formation of a dense accretion disc which gives birth to the young stars. Numerical hydrodynamical models indicate that this star formation process is rather fast and it precedes full circularization of the accretion flow, i.e. the new stars are born on elliptic orbits. By means of direct numerical N-body modeling, we show in this paper that the non-zero eccentricity of the stellar discs around the SMBH leads to an onset of various types of the Kozai-Lidov oscillations of a non-negligible subset of individual orbits in the disc, showing a remarkable robustness of this classical mechanism. Among others, we demonstrate that under certain circumstances, presence of an additional spherical cluster (which is generally known to damp Kozai-Lidov oscillations) may trigger such oscillations due to affecting the internal flow of the angular momentum through the disc. We conclude that the Kozai-Lidov oscillations are capable to substantially modify the initial structure of the disc (its thickness and distribution of eccentricities, in particular).