Disk Formation around Black Holes via Stream Accretion

We investigate accretion onto an isolated black hole under two distinct wind configurations: (a) uniform winds directed towards the black hole which can be described by the classical Bondi-Hoyle-Lyttleton (BHL) accretion, and (b) winds streaming past the black hole where only a smaller fraction of the flow can be captured by the black hole. This study employs a non-relativistic two-dimensional simulation code equipped with the relativistically correct equation of state having variable adiabatic index. We inject a continuous parallel wind having different compositions, such as electron-proton flow or a charge-neutral mixture of electron, positron, and proton into the simulation domain through an inflow boundary. We found that no disc-like structures form within the accretion flow when uniform winds are directed toward the black hole. However, in the case of winds streaming past the black hole, the flow initially forms a disc-like structure around the black hole. This disc later transforms into a shock cone due to the inflow pressure but reappears at a later time depending on the angular momentum distribution in different cases. These alternating phases of disc-like structure and shock cone significantly affect the bolometric luminosity of the system, causing variation by an order of magnitude.