With the help NASA’s Chandra X-ray Observatory astronomers discovered the first pair of supermassive black holes in a spiral galaxy similar to the Milky Way. Approximately 160 million light years from Earth, the pair is the nearest known such phenomenon. The black holes are located near the center of the spiral galaxy NGC 3393. NGC 3393 is a well-organized spiral galaxy, and its central bulge is dominated by old stars. The black holes are likely the remnant of a merger of two galaxies of unequal mass a billion or more years ago. Previous observations in X-rays and at other wavelengths indicated that a single supermassive black hole existed in the center of NGC 3393.
However, a long look by Chandra allowed the researchers to detect and separate the dual black holes. Both black holes are actively growing and emitting X-rays as gas falls towards them and becomes hotter. Both of the supermassive black holes are heavily obscured by dust and gas, which makes them difficult to observe in optical light. According to astronomers they are the closest supermassive black holes to Earth ever seen.