Explained: Two black holes merged billions of years ago. Why is this puzzling scientists?

News: Billions of years ago, collision between two black holes sent gravitational waves rippling through the universe.In 2019,signals from these waves were detected at the gravitational wave observatory LIGO (United States) and the detector Virgo(Italy). Facts: GW190521: It is a gravitational wave signal resulting from the merger of two black holes near a third supermassive… Continue reading Explained: Two black holes merged billions of years ago. Why is this puzzling scientists?