Supermassive black hole binary. Supercomputer simulation of two supermassive black holes orbiting as a binary pair, close to the point of merging. Regions of light-emitting gas (purple) glow as the black holes merge, all connected by streams of hot gas: a large ring encircling the entire system, called the circumbinary disk, and two smaller ones around each black hole, called mini disks. All these objects emit predominantly ultraviolet (UV) light. Some X-rays are also produced as the UV radiation interacts with each black hole's corona, a region of high-energy subatomic particles above and below the disk. Here, the emitted light represents all wavelengths. This simulation was run in 2018 on the National Center for Supercomputing Applications' Blue Waters supercomputer at the University of Illinois at Urbana-Champaign.