An artist's depiction of a supermassive black hole. (Image credit: NASA/JPL-Caltech)

Black holes more massive than entire galaxies are not a major component of the mysterious dark matter that's thought to make up most of the matter in the cosmos, a new study finds.

For decades, to explain why galaxies do not spin apart at the speeds at which they whirl, scientists have suggested the existence of an unseen substance known as dark matter , whose gravitational pull helps keep galaxies together. Dark matter is thought to make up about five-sixths of all matter in the universe .

Much remains unknown about dark matter, however — including whether or not it actually exists. Black holes make good potential contenders for dark matter, since they are extremely massive and are difficult to spot in the dark depths of space.

In the new study, researchers investigated whether dark matter could be made of " stupendously large black holes ," ones with masses greater than 100 billion times the mass of the sun .…