Supermassive Black Hole growth limits dark matter

Found an interesting article, at the daily galaxy. About a paper from from Dr. Xavier Hernandez and Dr. William Lee, (sorry, no article citation in the link, and couldn't find them with an ArXiv search), which looks at how the central black hole in the middle of a galaxy, absorbs dark matter. According to the Hernandez and Lee, if the density of dark matter in the centre of the galaxy, is greater than seven hole masses per cubic light year, the central black hole would grow fast than observation of black hole size predict. However ordinary theory of dark matter predict that concentration of dark matter is cuspy, tending to infinity as 1/r square, or so at the centres of galaxy. Thus some mechanism must intervene to prevent dark matter getting to dense. This could be annihilation of dark matter particles in the super-symmetric models, or formation of mirror stars, in the mirror matter model.