The Galactic Center Cloud G2 -- a Young Low-Mass Star with a Stellar Wind

TL;DR

This paper proposes that the G2 gas cloud near Sagittarius A* is actually a young T Tauri star with a stellar wind, and explores how its bow shock and emission features support this model, predicting its survival through pericenter.

Contribution

It introduces a novel model where G2 is a young star with a stellar wind, explaining observed emissions and predicting its survival during close approach to the black hole.

Findings

The bow shock emission measure matches observations.

The star's wind is likely to survive pericenter passage.

Emission characteristics depend on ionization mechanisms.

Abstract

We explore the possibility that the G2 gas cloud falling in towards \sgra is the mass loss envelope of a young TTauri star. As the star plunges to smaller radius at 1000 to 6000 \kms, a strong bow shock forms where the stellar wind is impacted by the hot X-ray emitting gas in the vicinity of \sgra. For a stellar mass loss rate of $4\times10^{-8}$ \msun per yr and wind velocity 100 \kms, the bow shock will have an emission measure ($EM = n^2 vol$) at a distance $\sim10^{16}$ cm, similar to that inferred from the IR emission lines. The ionization of the dense bow shock gas is potentially provided by collisional ionization at the shock front and cooling radiation (X-ray and UV) from the post shock gas. The former would predict a constant line flux as a function of distance from \sgra, while the latter will have increasing emission at lesser distances. In this model, the star and its mass loss wind should survive pericenter passage since the wind is likely launched at 0.2 AU and this is much less than the Roche radius at pericenter ($\sim3$ AU for a stellar mass of 2\msun). In this model, the emission cloud will probably survive pericenter passage, discriminating this scenario from others.