Browsing by Author "Burkert, A."

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    Clump formation through colliding stellar winds in the galactic centre
    (2016) Calderón Espinoza, Diego Nicolás; Ballone, A.; Cuadra Stipetich, Jorge Rodrigo; Schartmann, M.; Burkert, A.; Gillessen, S.
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    Clump formation through colliding stellar winds in the Galactic Centre
    (2017) Calderón Espinoza, Diego Nicolás; Ballone, A.; Cuadra, Jorge; Schartmann, Marc; Burkert, A.; Gillessen, S.
    We study the process of clump formation from hydrodynamic instabilities in stellar wind collisions, using analytical and numerical techniques. We show that the cloud G2 in the Galactic Centre could have been formed in this way, with the most promising sources being compact massive binaries, such as IRS 16SW....
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    The Accretion Mode in Sub-Eddington Supermassive Black Holes: Getting into the Central Parsecs of Andromeda
    (2023) Alig, C.; Prieto, A.; Blana, M.; Frischman, M.; Metzl, C.; Burkert, A.; Zier, O.; Streblyanska, A.
    The inner kiloparsec regions surrounding sub-Eddington (luminosity less than 10(-3) in Eddington units, L-Edd) supermassive black holes (BHs) often show a characteristic network of dust filaments that terminate in a nuclear spiral in the central parsecs. Here we study the role and fate of these filaments in one of the least accreting BHs known, M31 (10(-7) L (Edd)) using hydrodynamical simulations. The evolution of a streamer of gas particles moving under the barred potential of M31 is followed from kiloparsec distance to the central parsecs. After an exploratory study of initial conditions, a compelling fit to the observed dust/ionized gas morphologies and line-of-sight velocities in the inner hundreds of parsecs is produced. After several million years of streamer evolution, during which friction, thermal dissipation, and self-collisions have taken place, the gas settles into a disk tens of parsecs wide. This is fed by numerous filaments that arise from an outer circumnuclear ring and spiral toward the center. The final configuration is tightly constrained by a critical input mass in the streamer of several 10(3) M-circle dot (at an injection rate of 10(-4) M-circle dot yr(-1) 6 K is key to the development of a nuclear spiral during the simulation. The final inflow rate at 1 pc from the center is similar to 1.7 x 10(-7) M-circle dot yr(-1), consistent with the quiescent state of the M31 BH.
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    Three-dimensional simulations of clump formation in stellar wind collisions
    (OUP, 2020) Calderón Espinoza, Diego Nicolás; Cuadra Stipetich, Jorge Rodrigo; Schartmann, M.; Burkert, A.; Prieto, J.; 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 three-dimensional high-resolution hydrodynamical simulations of stellar wind collisions with the adaptive-mesh refinement grid-based code ramses. We aim at characterizing 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 on to the central supermassive black hole.