An Eccentric-Disk Model for the Nucleus of M31

Abstract

The nucleus of M31 may be a thick eccentric disk, composed of stars traveling on nearly Keplerian orbits around a black hole or other dark compact object. This hypothesis reproduces most of the features seen in HST photometry of the center of M31; in particular the bright off-center source P1 is the apoapsis region of the disk. An eccentric disk can also explain the rotation curve and asymmetric dispersion profile revealed by ground-based observations. The central object must be smaller than ~1 pc so that the potential felt by the disk is nearly Keplerian. The disk eccentricity may be excited by dynamical friction from the bulge.