Three giant black holes have been spotted within a titanic collision of three galaxies. This discovery was made using data from NASA's Chandra X-ray Observatory and other telescopes both on the ground and in space. To uncover this rare black hole trifecta, researchers first needed information from the Sloan Digital Sky Survey telescope in New Mexico that scans large swaths of the sky in optical light. With the help of citizen scientists across the globe as part of the Galaxy Zoo Project, the system known as SDSS J0849+1114 was tagged as a system of colliding galaxies. Then astronomers turned to infrared data from NASA's WISE mission, which revealed that the system was glowing intensely in the infrared during a phase in the galaxy merger when more than one of the black holes is expected to be feeding rapidly. To follow up on these clues, astronomers then turned to Chandra and the Large Binocular Telescope, or LBT, in Arizona. The Chandra data revealed X-ray sources — a tell-tale sign of material being consumed by the black holes — at the bright centers of each galaxy in the merger, exactly where scientists expect supermassive black holes to reside. Chandra and NASA's NuSTAR also found evidence for large amounts of gas and dust around one of the black holes, typical for a merging black hole system. One reason it is difficult to find a triplet of supermassive black holes is that they are often shrouded in gas and dust, and this blocks much of the light from the regions around them. The infrared images of WISE, the infrared spectra from LBT and the X-ray images from Chandra bypass this issue, because infrared and X-ray light pierce clouds of gas much more easily than optical light. Astronomers think these triplet collisions, while extremely rare, play a critical role in how the biggest black holes grow over time. Because of that, they will continue to use Chandra and other telescopes to search for these important systems.
