The role of interacting stellar winds feeding Sagittarius A*.
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2019
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Abstract
The central parsec of the Milky Way is among the most enigmatic regions in the entire Galaxy. The existence of the central super-massive black hole, Sgr A*, and its proximity allow us to use it as a laboratory for understanding the astrophysics of galactic nuclei, in general. Although it is well known that this is a very hostile environment due to the presence of tens ofWolf-Rayet (WR) stars with strong outflows, the recent detection of cold gas (-104 K) has challenged our understanding of the gas dynamics and thermodynamics of the region. The so-called G2 source, the dusty sources in the IRS 13E cluster, as well as the disc-like structure in the immediate vicinity of Sgr A* are examples of such cold material. In this thesis, we present a detailed study of the formation of cold gas as a potential result of the collision of the many stellar winds, which are constantly taking place. The main aims of this study are: i) testing the hypothesis of G2 being a gaseous clump formed in a massive binary system, ii) constraining the initial properties and final fate of clumps formed in unstable wind interactions, iii) establishing whether it is possible or not for the system of WR stars orbiting Sgr A* to reach and remain in a steady state between the supplying and inflowing/outflowing material. We find that the properties and dynamics of the clumps produced in the known massive binaries are not consistent with G2’s, ruling out this hypothesis. Additionally, we perform adaptive-mesh refinement hydrodynamical simulations of idealised stellar wind collisions in order to characterise the clump formation process. The results show that clumps formed through thin-shell instabilities are not massive enough to impact significantly the state of the material enclosed within the inner parsec. Finally, the simulation of the complete system of WR stars orbiting Sgr A* shows that the natural outcome of its long-term evolution is the accumulation of material at its centre. Thus, we speculate that the WR stars and their outflows could explain all the phenomenology related to the activity of Sgr A* inferred from observations without the need of invoking external agents.
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Tesis (Doctor in Astrophysics)--Pontificia Universidad Católica de Chile, 2019