Pavel Kroupa of the University of Bonn, and colleagues, analysed the notion of dwarf galaxies, thousands of stars that orbit the Milky Way. These are apparently orbiting in a plane rather than being evenly distributed – which is a problem for calculations. These seem to show such small galaxies do not contain dark matter yet, observations of their orbital speed implies they should contain dark matter as the extent material is not enough to explain the velocities inferred. See various sources such as www.dailygalaxy.com/my_weblog/2011/07/dwarf-galaxies-orbiting-the-milky-…. Dwarf galaxies are faint companions of the Milky Way that were discovered by sky searches such as the Sloan Digital Sky Survey – but see also http://holographicgalaxy.blogspot.com and http://hologramuniverse.wordpress.com.