Free Astronomy Magazine March-April 2022

53 ASTRO PUBLISHING jects by looking at how the gravita- tional pull of the black holes influ- ences the motion of the stars around them. The bigger black hole, located right at the core of NGC 7727, was found to have a mass almost 154 million times that of the Sun, while its companion is 6.3 million solar masses. It is the first time the masses have been measured in this way for a su- permassive black hole pair. This feat was made possible thanks to the close proximity of the system to Earth and the detailed observations the team obtained at the Paranal Observatory in Chile using the Multi- Unit Spectroscopic Explorer (MUSE) on ESO’s VLT, an instrument Voggel learnt to work with during her time as a student at ESO. Measuring the masses with MUSE, and using addi- tional data from the NASA/ESA Hub- ble Space Telescope, allowed the team to confirm that the objects in U sing the ESO’s Very Large Telescope, astronomers have revealed the closest pair of supermassive black holes to Earth ever observed. This video sum- marises the discovery. [ESO] NGC 7727 were indeed supermassive black holes. Astronomers suspected that the galaxy hosted the two black holes, but they had not been able to confirm their presence until now since we do not see large amounts of high-energy radiation coming from their immediate surroundings, which would otherwise give them away. “Our finding implies that there might be many more of these relics of galaxy mergers out there and they may contain many hidden massive black holes that still wait to be found,” says Voggel. “It could in- crease the total number of super- massive black holes known in the local Universe by 30 percent.” The search for similarly hidden su- permassive black hole pairs is ex- pected to make a great leap for- ward with ESO’s Extremely Large Telescope (ELT), set to start operat- ing later this decade in Chile’s Ata- cama Desert. “This detection of a supermassive black hole pair is just the beginning,” says co-author Stef- fen Mieske, an astronomer at ESO in Chile and Head of ESO Paranal Sci- ence Operations. “With the HAR- MONI instrument on the ELT we will be able to make detections like this considerably further than currently possible. ESO’s ELT will be integral to understanding these objects.” !