Bondi accretion in the finite luminous region of elliptical galaxies

Abstract

Abstract The classical Bondi model is adopted to study accretion onto the finite luminous region around the central massive black hole (MBH) in an elliptical galaxy. Unlike Bondi (1952), we define the boundary conditions at a certain finite radius (rf) instead of at the infinity and examine the variation of solutions for a simple case. In the following, we consider the special case of a MBH at the center of a Hernquist galaxy and involve the gravity and luminosity of its own galaxy. Our results in the first part show that kinitic energy at the final radius is ignorable even for not so far away from the center. Moreover, the mass accretion rate will be approximately equal to its Bondi value if the final radius (rf) becomes about 2-3 orders of magnitude larger than semi-Bondi radius, i.e. $GM/c_{sf}^2$ (where M and csf are the mass of the central object and the sound speed at rf). In the second part, adding the two extra forces of gravity and radiation in the momentum equation let us know that the maximum possible of accretion rate increases with greater characteristic linear density of galaxy and lower radiation.