SAT Inferences Question

Musician and astronomer Darsan Swarop Bellie researches gravitational waves. These invisible waves move very quickly through space. They cannot be viewed through a telescope, but they do make sounds that can be detected with special equipment. In his musical composition Dance of the Black Holes, Bellie demonstrates what gravitational waves might sound like as two black holes merge in space. With this composition and others, Bellie hopes to make aspects of science more accessible. According to the text, what is the subject of Bellie's research?