NASA said its Hubble Space Telescope and Chandra X-ray Observatory detected a pair of supermassive black holes that are closer together than previously discovered duos.Its the closest detected pair of black holes found in the local universe, although several dozen black hole duos have been discovered before.The black holes are buried deep in a pair of colliding galaxies that are fueled by infalling gas and dust, NASA said in a press release. The phenomenon makes them shine brightly as active galactic nuclei.RELATED STORY | Polaris space mission will provide the first private space walkNASA said black hole duos like this one were likely more common in the early universe when galaxy mergers were more frequent.The two supermassive black holes were once at the core of their respective host galaxies, but NASA said a merger between the galaxies brought the black holes into close proximity.They will continue to spiral closer together until they eventually merge in perhaps 100 million years rattling the fabric of space and time as gravitational waves, said NASA in a press release.RELATED STORY | The Starliner space capsule has returned to Earth without its crewNASA also announced that its Europa Clipper spacecraft passed a key milestone this week and it is on track to launch in October to explore signs of habitability on one of Jupiters moons.