http://arxiv.org/abs/1906.04181
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 $(\dot{M}\sim10^{-5}\rm\ M_{\odot}\ yr^{-1})$, wind speeds of $\sim500$-$1500\rm\ km\ s^{-1}$, and stellar separations of $\sim20$-$200\rm\ au$. We develop 3D high resolution hydrodynamical simulations of stellar wind collisions, making use of 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. Our results confirm that more massive clumps are formed in systems whose winds are close to the transition between the radiative and adiabatic regimes, as long as such collisions are capable of creating cold, thin shells. Also, we find that increasing either the wind speed or the degree of asymmetry in the wind interaction increases the dispersion of the clump masses and ejection speed distribution. Nevertheless, our findings show that the most massive clumps are very light $(\sim10^{-3}$-$10^{-2}\rm\ M_{\oplus})$, approximately three orders of magnitude less massive than theoretical upper limits. We apply our results to the central parsec of our Galaxy finding that clumps formed are not heavy enough neither to affect the thermodynamic state of the region nor to survive for long enough in order to fall onto the central super-massive black hole before being destroyed.
D. Calderón, J. Cuadra, M. Schartmann, et. al.
Wed, 12 Jun 19
32/59
Comments: 21 pages, 20 Figures, 2 Tables. Manuscript submitted to MNRAS