Dark Matter Reefs

The Dark Matter Reefs were a collection of similar astronomical phenomena in close proximity to each other.

Based on the way that Professor Yana described their general location to the Tenth Doctor, Martha and Jack in about the year 100,000,000,000,000, they were far from the planet Malcassairo. He suggested that the planet Utopia was between the Condensate Wilderness on the near side of Malcassairo and "the Wildlands" and the Reefs on the far side. (TV: Utopia)