Browsing by Author "Burkert, Andreas"

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    3D simulations of clump formation in stellar wind collisions
    (2019) Calderón Espinoza, Diego Nicolás; Cuadra, Jorge; Schartmann, Marc; Burkert, Andreas; Prieto Brito, Joaquín; Russell, Christopher M. P.
    The inner parsec of our Galaxy contains tens of Wolf-Rayet stars whose powerful outflows are constantly interacting while filling the region with hot, diffuse plasma. Theoretical models have shown that, in some cases, the collision of stellar winds can generate cold, dense material in the form of clumps. However, their formation process and properties are not well understood yet. In this work we present, for the first time, a statistical study of the clump formation process in unstable wind collisions. We study systems with dense outflows (∼10−5 M yr−1 ), wind speeds of 500–1500 km s−1, and stellar separations of ∼20–200 au. We develop 3D high resolution hydrodynamical simulations of stellar wind collisions with the adaptive-mesh refinement grid-based code RAMSES. We aim to characterise the initial properties of clumps that form through hydrodynamic instabilities, mostly via the non-linear thin shell instability (NTSI). Our results confirm that more massive clumps are formed in systems whose winds are close to the transition between the radiative and adiabatic regimes. Increasing either the wind speed or the degree of asymmetry increases the dispersion of the clump mass and ejection speed distributions. Nevertheless, the most massive clumps are very light (∼10−3–10−2 M⊕), about three orders of magnitude less massive than theoretical upper limits. Applying these results to the Galactic Centre we find that clumps formed through the NTSI should not be heavy enough either to affect the thermodynamic state of the region or to survive for long enough to fall onto the central super-massive black hole.
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    The Galactic Centre source G2 was unlikely born in any of the known massive binaries
    (2018) Calderón Espinoza, Diego Nicolás; Cuadra, Jorge; Schartmann, Marc; Burkert, Andreas; Plewa, P.; Eisenhauer, F.; Habibi, M.
    The source G2 has already completed its pericentre passage around Sgr A*, the supermassive black hole in the centre of our Galaxy. Although it has been monitored for 15 yr, its astrophysical nature and origin still remain unknown. In this work, we aim to test the hypothesis of G2 being the result of a stellar wind collision. To do so, we study the motion and final fate of gas clumps formed as a result of collisions of stellar winds in massive binaries. Our approach is based on a test-particle model in order to describe the trajectories of such clumps. The model takes into account the gravitational field of Sgr A*, the interaction of the clumps with the interstellar medium as well as their finite lifetimes. Our analysis allows us to reject the hypothesis based on four arguments: (i) if G2 has followed a purely Keplerian orbit since its formation, it cannot have been produced in any of the known massive binaries since their motions are not consistent, (ii) in general, gas clumps are evaporated through thermal conduction on very short timescale (⁠<100yr⁠) before getting close enough to Sgr A*, (iii) IRS 16SW, the best candidate for the origin of G2, cannot generate clumps as massive as G2, and (iv) clumps ejected from IRS 16SW describe trajectories significantly different to the observed motion of G2.