3D simulations of clump formation in stellar wind collisions
  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 (${\sim}10^{-5}\rm\ M_{\odot}\ yr^{-1}$), wind speeds of
$500$-$1500\rm\ km\ s^{-1}$, and stellar separations of ${\sim}20$-$200\rm\
au$. 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 (${\sim}10^{-3}$-$10^{-2}\rm\ M_{\oplus}$), 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.
