Stars and Disks around Massive Black Holes (Poster paper)

Summary

ABSTRACT

We calculated the orbital evolution of stars due to interaction with an accretion disk around a massive black hole in a galactic nucleus. After circularization the radius of a stellar orbit with initial inclination i to the disk shrinks by a factor 4/(1 + cos i)² before it settles in the plane of the accretion disk. Next, we calculate the rate at which stars from the star cluster around the hole are captured by a standard Shakura-Sunyaev disk. We find that the majority of captured stars are on retrograde orbits. These stars may reach a small separation from the hole before settling in the disk. AGN with M ∼ 10⁶ M_⊙ and Ṁ = M_Edd are likely to have stars on inclined orbits with small separation from the hole, i.e. just outside the tidal disruption radius. Observational effects will be most conspicuous in low luminosity AGN.

EVOLUTION OF STAR ORBIT

The pre- and post-impact velocities v and v₁ can be calculated from conservation of momentum: m_*v + Δmw = (m_*, + Δm)v₁, where Δm is the mass swept up by the star and w is the velocity of the accretion disk at the impact point. These three equations together with the requirement that the pre– and post–impact positions are the same, provide a set of four relations between the old and new orbital parameters. It is possible to find explicit expressions for the changes in the orbital parameters by linearizing these equations (Roos and Kaastra 1993, in preparation).