Depletion of bright red giants in the Galactic center during its active phases

TL;DR

This paper proposes that past activity of Sgr A* involved jets that ablated red giant envelopes, explaining the observed flat core of bright late-type stars near the Galactic center.

Contribution

It introduces a jet-star interaction scenario that accounts for the depletion of bright red giants in the Galactic center during active phases.

Findings

Red giant envelopes can be ablated by jets with luminosity 10^{41}-10^{44} erg/s.

Jet interactions reduce infrared luminosity of red giants over thousands of events.

Additional tidal and disc interactions contribute to the flat stellar density profile.

Abstract

Observations in the near-infrared domain showed the presence of the flat core of bright late-type stars inside $\sim 0.5\,{\rm pc}$ from the Galactic center supermassive black hole (Sgr A*), while young massive OB/Wolf-Rayet stars form a cusp. Several dynamical processes were proposed to explain this apparent paradox of the distribution of the Galactic center stellar populations. Given the mounting evidence about a significantly increased activity of Sgr A* during the past million years, we propose a scenario based on the interaction between the late-type giants and a nuclear jet, whose past existence and energetics can be inferred from the presence of $\gamma$-ray Fermi bubbles and bipolar radio bubbles. Extended, loose envelopes of red giant stars can be ablated by the jet with kinetic luminosity in the range of $L_{\rm j}\approx 10^{41}$-$10^{44}\,{\rm erg\,s^{-1}}$ within the inner $\sim 0.04\,{\rm pc}$ of Sgr A* (S cluster region), which would lead to their infrared luminosity decrease after several thousand jet-star interactions. The ablation of the atmospheres of red giants is complemented by the process of tidal stripping that operates at distances of $\lesssim 1\,{\rm mpc}$, and by the direct mechanical interaction of stars with a clumpy disc at $\gtrsim 0.04\,{\rm pc}$, which can explain the flat density profile of bright late-type stars inside the inner half parsec from Sgr A*.