3D hydrodynamical simulations of the impact of mechanical feedback on
  accretion in supersonic stellar-mass black holes
  Isolated stellar-mass BH accrete gas, often at supersonic speeds, and can
form outflows that can influence the accreted gas. The latter process, known as
mechanical feedback, can significantly affect the accretion rate. We use
hydrodynamical simulations to assess the impact of mechanical feedback on the
accretion rate when the BH moves supersonically through a uniform medium. We
carry out 3D hydrodynamical simulations of outflows fueled by accretion that
interact with a uniform medium, probing scales similar to and larger than the
accretor gravitational sphere of influence. In the simulations the accretor is
at rest and the medium moves at supersonic speeds. The outflow power is assumed
to be proportional to the accretion rate. The simulations are run for different
outflow-medium motion angles and velocity ratios. The impact of different
degrees of outflow collimation, accretor size, and resolution is also
investigated. In general, the accretion rate is significantly affected by
mechanical feedback. The effect is small for outflows perpendicular to the
medium motion, and quickly grows for smaller angles. Moreover, the smaller the
medium-to-outflow velocity ratio is, the more accretion decreases. On the other
hand, the impact of outflow collimation seems moderate. The effect is enhanced
when the accretor size is reduced. For a population of BH with random outflow
orientations, the average accretion rate drops by (high-low resolution)
~0.2-0.4 and ~0.1-0.2 for medium-to-outflow velocity ratios of 1/20 and 1/100,
respectively, when compared to the corresponding cases without outflow. Our
results strongly indicate that, on the considered scales, mechanical feedback
can easily reduce the energy available from supersonic accretion by a factor of
several. This should be taken into account when studying the mechanical,
thermal and non-thermal output of isolated BH.
