Journal Article

On the number of young stellar discs in the Galactic Centre

U. Löckmann and H. Baumgardt

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 394, issue 4, pages 1841-1846
Published in print April 2009 | ISSN: 0035-8711
Published online April 2009 | e-ISSN: 1365-2966 | DOI:
On the number of young stellar discs in the Galactic Centre

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Observations of the Galactic Centre show evidence of disc-like structures of very young stars orbiting the central supermassive 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 recognized 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.

Keywords: black hole physics; stellar dynamics; methods: N-body simulations; Galaxy: centre

Journal Article.  4165 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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