What is an example of a binary black hole system?

A binary black hole system consists of two black holes that are in close orbit around each other. NGC 6240 is an excellent example of this type of system, as it has been identified in observations as featuring two supermassive black holes at its center, which are merging. The discovery of such systems is important in astrophysics because they allow astronomers to study the dynamics of black holes, gravitational wave emissions, and the evolution of galaxies.

In contrast, the other options do not fit the criteria for a binary black hole system. The Andromeda Galaxy and the Whirlpool Galaxy are large galaxies that may contain supermassive black holes at their cores, but they are not specifically recognized as binary systems. The Great Attractor is a gravitational anomaly in intergalactic space that is influencing the motion of galaxies, but it is not associated with the presence of binary black holes. Therefore, NGC 6240 stands out as the correct answer due to its direct observation of two black holes in close proximity to each other, highlighting the significance of this phenomenon in the study of cosmic structures.