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

摘要

We present 3D, adaptive mesh refinement simulations of G2, a cloud of gasmoving in a highly eccentric orbit towards the galactic center. We assume thatG2 originates from a stellar wind interacting with the environment of the SgrA* black hole. The stellar wind forms a cometary bubble which becomesincreasingly elongated as the star approaches periastron. A few months afterperiastron passage, streams of material begin to accrete on the central blackhole with accretion rates $\dot{M} \sim 10^{-8}$ M$_\odot$ yr$^{-1}$. PredictedBr$\gamma$ emission maps and position-velocity diagrams show an elongatedemission resembling recent observations of G2. A large increase in luminosityis predicted by the emission coming from the shocked wind region duringperiastron passage. The observations, showing a constant Br$\gamma$ luminosity,remain puzzling, and are explained here assuming that the emission is dominatedby the free-wind region. The observed Br$\gamma$ luminosity ($\sim 8 \times10^{30}$ 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 theemission comes from the shocked wind. A faster and less dense wind reproducesthe Br$\gamma$ luminosity if the emission comes from the inner, free windregion. The extended cometary wind bubble, largely destroyed by the tidalinteraction with the black hole, reforms a few years after periastron passage.As a result, the Br$\gamma$ emission is more compact after periastron passage.