The Origin of the Young Stars in the Nucleus of M31

Abstract

The triple nucleus of M31 consists of a population of old red stars in an eccentric disk (P1 and P2) and another population of younger A stars in a circular disk (P3) around M31's central supermassive black hole (SMBH). We argue that P1 and P2 determine the maximal radial extent of the younger A star population and provide the gas that fueled the starburst that generated P3. The eccentric stellar disk creates an $m=1$ non-axisymmetric perturbation to the potential. This perturbed potential drives gas into the inner parsec around the SMBH, if the pattern speed of the eccentric stellar disk is $\Omega_p \lesssim 3-10 {\rm km s^{-1} pc^{-1}}$. We show that stellar mass loss from P1 and P2 is sufficient to create a gravitationally unstable gaseous disk of $\sim 10^5\Msun$ every $0.1-1$ Gyrs, consistent with the 200 Myr age of P3. Similar processes may act in other systems to produce very compact nuclear starbursts.