4C +37.11 or Galaxy 0402+379 is a radio galaxy and elliptical galaxy featuring binary supermassive black holes with the least separation of any directly observed binaries, as of 2006. The separation between the two is 24 light-years or 7.3 parsecs, with an orbital period of 150,000 years.
The previous directly observed least separation of supermassive binary black holes was 2,400 light-years. However, quasar OJ 287 is inferred to have a binary supermassive black hole pair with an orbital period of 12 years, and thus be much closer together, but they have not been directly observed.
The eventual collision of the pair would result in strong gravitational waves.