A Stellar Wind Origin for the G2 Cloud: Three-Dimensional Numerical Simulations

Abstract

We present 3D, adaptive mesh refinement simulations of G2, a cloud of gas moving in a highly eccentric orbit towards the galactic center. We assume that G2 originates from a stellar wind interacting with the environment of the Sgr A* black hole. The stellar wind forms a cometary bubble which becomes increasingly elongated as the star approaches periastron. A few months after periastron passage, streams of material begin to accrete on the central black hole with accretion rates $\dot{M}\sim 10^{-8}$ M${}_{\odot }$ yr${}^{-1}$. Predicted Br$\gamma$ emission maps and position-velocity diagrams show an elongated emission resembling recent observations of G2. A large increase in luminosity is predicted by the emission coming from the shocked wind region during periastron passage. The observations, showing a constant Br$\gamma$ luminosity, remain puzzling, and are explained here assuming that the emission is dominated by the free-wind region. The observed Br$\gamma$ luminosity ($\sim 8\times 10^{30}$ erg s${}^{-1}$) is reproduced by a model with a $v_w=50$ km s${}^{-1}$ wind velocity and a $10^{-7}$ M${}_{\odot }$ yr${}^{-1}$ mass loss rate if the emission comes from the shocked wind. A faster and less dense wind reproduces the Br$\gamma$ luminosity if the emission comes from the inner, free wind region. The extended cometary wind bubble, largely destroyed by the tidal interaction with the black hole, reforms a few years after periastron passage. As a result, the Br$\gamma$ emission is more compact after periastron passage.

6 pages, 5 figures, submitted to the Astrophysical Journal Letters

References in corpus (2)

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• The dynamics of internal working surfaces in MHD jets

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