Complex sentence: In the majority of other known black hole binaries, the companion star is large, massive and bright, this brings to question if the companion existed alongside star that created Black Hole or it was born out of supernova remnant.
Split into simpler sentences: In the majority of other known black hole binaries, the companion star is large, massive and bright. It is not known if the companion existed alongside the star that created the black hole or it was born out of a supernova remnant.