On the number of young stellar discs in the Galactic Centre

TL;DR

This study uses N-body simulations to investigate the structure of young stellar discs in the Galactic Centre, suggesting that apparent warping and eccentricities can be explained without requiring two distinct discs.

Contribution

The paper demonstrates through simulations that two inclined stellar discs cannot remain flat and circular after interaction, challenging the idea of two separate young stellar discs.

Findings

Two highly inclined discs warp significantly over 5 Myr.

Eccentricities in the clockwise disc can arise from relaxation processes.

The observed structures may originate from a single initial disc.

Abstract

Observations of the Galactic Centre show evidence of disc-like structures of very young stars orbiting the central super-massive black hole within a distance of a few 0.1 pc. While it is widely accepted that about half of the stars form a relatively flat disc rotating clockwise on the sky, there is a substantial ongoing debate on whether there is a second, counter-clockwise disc of stars. By means of N-body simulations using our bhint code, we show that two highly inclined stellar discs with the observed properties cannot be recognised as two flat circular discs after 5 Myr of mutual interaction. Instead, our calculations predict a significant warping of the two discs, which we show to be apparent among the structures observed in the Galactic Centre. While the high eccentricities of the observed counter-clockwise orbits suggest an eccentric origin of this system, we show the eccentricity distribution in the inner part of the more massive clockwise disc to be perfectly consistent with an initially circular disc in which stellar eccentricities increase due to both non-resonant and resonant relaxation. We conclude that the relevant question to ask is therefore not whether there are two discs of young stars, but whether there were two such discs to begin with.