부산대학교 도서관

Accreting black hole sources show variable outflows at different mass scales. For instance, in the case of galactic nuclei, our own galactic center Sgr A* exhibits flares and outbursts in the X-ray and infrared bands. Recent studies suggest that the inner magnetospheres of these sources have a pronounced effect on such emissions. Accreting plasma carries the frozen-in magnetic flux along with it down to the black hole horizon. During the in-fall, the magnetic field intensifies and it can lead to a magnetically arrested state. We investigate the competing effects of inflows at the black hole horizon and the outflows developed in the accreting plasma due to the action of magnetic field in the inner magnetosphere and their implications. We start with a spherically symmetric Bondi-type inflow and introduce the magnetic field. In order to understand the influence of the initial configuration, we start the computations with an aligned magnetic field with respect to the black hole rotation axis. Then we proceed to the case of magnetic fields inclined to the black hole rotation axis. We employ the 2D and 3D versions of HARM code for the aligned field models while using the 3D version for the inclined field and compare the results of computations against each other. We observe how the magnetic lines of force start accreting with the plasma while an equatorial intermittent outflow develops and goes on pushing some material away from the black hole partially along the equatorial plane, and partly ejecting it out of the plane in the vertical direction. In consequence, the accretion rate also fluctuates. The black hole spin direction prevails at later stages and it determines the flow geometry near the event horizon, whereas on larger scales the flow geometry stays influenced by the initial inclination of the field.
Comment: Submitted to Astronomy & Astrophysics