Among some of the most interesting things in space today are black holes and gravitational waves, but scientists now believe that there could be a connection between the two and that dark matter has something to do with it.
While dark energy is currently being challenged in the scientific community, dark matter is something completely different. Dark matter is essentially all the matter that exists in the universe that we can't see because the universe is a very dark place. Scientists estimate that dark matter makes up as much as 85% of the unseen universe.
One of the big clues to this idea is the hypothetical existence of a subatomic particle called an axion, which is many times smaller than an electron. It's believed that when these particles meet a black hole, they multiply and then form axion clouds. Inside of these, axions can slam into each other, and this might cause gravitational waves.
On the other hand, most of this is still hypothetical, as these gravitational waves aren't quite powerful enough for LIGO to detect like it has much larger gravitational waves previously. Perhaps someday, when LIGO undergoes some sensitivity upgrades, we'll be able to confirm or deny these theories.