Abstract
Young massive stars in the central parsec of our Galaxy are best explained by star formation within at least one, and possibly two, massive self-gravitating gaseous discs. With help of numerical simulations, we here consider whether the observed population of young stars could have originated from a large angle collision of two massive gaseous clouds at R ≃ 1 pc from Sgr A*. In all the simulations performed, the post-collision gas flow forms an inner, nearly circular gaseous disc and one or two eccentric outer filaments, consistent with the observations. Furthermore, the radial stellar mass distribution is always very steep, Σ * oc R -2 , again consistent with the observations. All of our simulations produce discs that are warped by between 30° and 60°, in accordance with the most recent observations. The three-dimensional velocity structure of the stellar distribution is sensitive to initial conditions (e.g. the impact parameter of the clouds) and gas cooling details. For example, the runs in which the inner disc is fed intermittently with material possessing fluctuating angular momentum result in multiple stellar discs with different orbital orientations, contradicting the observed data. In all the cases the amount of gas accreted by our inner boundary condition is large, enough to allow Sgr A* to radiate near its Eddington limit over ∼10 5 yr. This suggests that a refined model would have physically larger clouds (or a cloud and a disc such as the circumnuclear disc) colliding at a distance of a few parsecs rather than 1 pc as in our simulations.
Highlights
The power output of the central parsec of our Galaxy is dominated by young massive ‘He–I’ stars (Krabbe et al 1995)
The bright He–I stars seem to be excluded from the central arcsecond [1 arcsec ≈ 0.04 pc when viewed from the ≈8 kpc distance to the Galactic Centre (GC)], which instead contains at least a dozen less massive but still quite young B-type stars (Ghez et al 2003, 2005)
In this paper we presented several simulations of cloud–cloud collisions aimed at reproducing gas flows that could have formed gaseous disc(s) in the central parsec of our Galaxy, as well as the resulting star formation
Summary
The power output of the central parsec of our Galaxy is dominated by young (aged 6 ± 1 Myr) massive ‘He–I’ stars (Krabbe et al 1995) Many of these stars are located in a well-defined thin disc structure that rotates clockwise as seen on the sky (Genzel et al 2003; Levin & Beloborodov 2003; Paumard et al 2006). The bright He–I stars seem to be excluded from the central arcsecond [1 arcsec ≈ 0.04 pc when viewed from the ≈8 kpc distance to the Galactic Centre (GC)], which instead contains at least a dozen less massive but still quite young B-type stars (Ghez et al 2003, 2005) These stars (commonly referred to as S-stars in the GC community) appear to be on rather eccentric orbits distributed without any notable preference to a planar configuration (e.g. Eisenhauer et al 2005; Lu et al 2006). At present it is not clear if the S-stars are physically related to the more massive ‘disc’-stars,
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