Stupendously large black holes are not a major part of dark matter, study finds

An analysis of the cosmic microwave background shows that black holes more massive than 100 billion suns cannot make up a significant fraction of dark matter, since they would make the early universe's light grainy, which is not observed. The study will be published Oct. 26 in Physical Review Letters.

• Researchers examined black holes heavier than 100 billion solar masses
• The largest known black hole weighs about 36 billion suns
• The cosmic microwave background shows no expected graininess
• Scientists are now testing asteroid-sized black holes as a candidate