Universe Today - 2010 April 04
The Nuclear Stellar Disk in Andromeda: A Fossil from the Era of Black Hole GrowthIn 1993, the Hubble Space Telescope snapped a close-up of the nucleus of the Andromeda galaxy, M31, and found that it is double.
In the 15+ years since, dozens of papers have been written about it, with titles like The stellar population of the decoupled nucleus in M 31, Accretion Processes in the Nucleus of M31, and The Origin of the Young Stars in the Nucleus of M31.
And now there's a paper which seems, at last, to explain the observations; the cause is, apparently, a complex interplay of gravity, angular momentum, and star formation.
- arXiv.org > astro-ph > arXiv:1002.1079v2 > 31 Mar 2010