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