At www.io9.com/5988736/has-the-milky-way-devoured-other-galaxies?utm … a study in the Monthly Notices of the Royal Astronomical Society claims the Milky Way has absorbed smaller galaxies – but millions of years ago. Not only that, speculation is that the two black holes of the two galaxies became a single black hole. Old stars were blasted from the core region at hypervelocity speeds. Two giant lobes of energetic diffuse gamma-ray light are at the heart of our galaxy, straight above and below the galactic plane. The edges of the bubbles are super sharp – like teeth. Most of the smaller galaxy was funnelled into the supermassive black hole – having a gas rich meal.
On a slightly different tack but also involving the centre of the galaxy and the black hole hypothesized as residing there, we learn that astrophysicists at Fermi suggest there is a massive outflow of charged particles from the centre of the Milky Way which may be due to collisions between dark matter – leading to their annihilation. Is that why we can't see them? (http://phys.org/print281865985.html) but the article can be viewed on the prepublication server arxiv.org/abs/1302.6589