Oral Presentation

Wandering of the central black hole in a galactic nucleus and the correlation of the black hole mass with the bulge mass

Author(s): Hajime Inoue (ISAS, JAXA)

Presenter: Hajime Inoue (ISAS, JAXA (Prof. Emeritus))

A mechanism for a super-massive black hole at the center of a galaxy to wander in the nucleus region is investigated.
A situation is supposed that the central black hole tends to move by the gravitational attractions from the nearby molecular clouds in a nuclear bulge but is braked via the dynamical frictions by ambient stars there.
We approximately estimate the kinetic energy of the black hole in an equilibrium between the energy gain rate through the gravitational attractions and the energy loss rate through the dynamical frictions, in a nuclear bulge composing of a nuclear stellar disk and a nuclear stellar cluster as observed from our Galaxy.
The wandering distance of the black hole in the gravitational potential of the nuclear bulge is evaluated to get as large as several 10 pc, when the black hole mass is relatively small.
The distance, however, shrinks as the black hole mass increases and
the equilibrium solution between the energy gain and loss disappears when the black hole mass exceeds an upper limit.
As the result, we can expect the following scenario for the evolution of the black hole mass:
When the black hole mass is smaller than the upper limit, mass accretion of the interstellar matter in the circum-nuclear region, causing the AGN activities, makes the black hole mass larger.
However, when the mass gets to the upper limit mass, the black hole loses the balancing force against the dynamical friction and starts spiraling downward to the gravity center. From simple parameter scaling, the upper limit mass of the black hole is found to be proportional to the bulge mass and it could explain the observed correlation of the black hole mass with the bulge mass.