The pair of supermassive black holes in the galaxy NGC 7727 in the constellation of Aquarius is about 89 million light-years from Earth. It may seem far away, but on a cosmic scale it is not – especially as this result quite significantly beats the existing record for the closest arrangement of such objects to us (470 million light years), making the newly found closest pair of the known ones.
Supermassive black holes lurk in the cores of large galaxies, and when such galaxies merge, the black holes hit a collision course. The pair in NGC 7727 breaks the record for the smallest known separation between two supermassive black holes – observations indicate that the distance between them is within 1,600 light years.
“For the first time, we found two supermassive black holes that are close together, less than half of the separation in existing record holders,” said Karina Voggel, astronomer at Strasbourg Observatory in France and lead author of a study published at the end of November this year. in the periodical Astronomy & Astrophysics. “The small separation and speed of the two black holes indicate that they will merge into a monstrous black hole, which is likely to happen in the next 250 million years,” said another co-author, Holger Baumgardt, professor at the University of Queensland (Australia).
Black hole merging, such as the one described, may explain how the most massive black holes in the universe are formed. Voggel and her team were able to determine the masses of the two objects by analyzing how the gravitational pull of black holes affects the movement of stars around them. For the larger black hole, located precisely at the core of NGC 7727, it was possible to establish a mass nearly 154 million times that of the Sun. Its companion, on the other hand, has about 6.4 million solar masses.
This is the first time masses have been measured in this way for a pair of supermassive black holes. This was made possible by the system’s proximity to the Earth and the team’s detailed observations at the Paranal Observatory in Chile with the Multi-Unit Spectroscopic Explorer (MUSE) on the VLT. By determining the masses with MUSE and using additional data from the Hubble Space Telescope, the team of scientists was able to confirm that the objects in NGC 7727 are in fact supermassive black holes.
Astronomers suspected that the galaxy has two black holes, but until now have not been able to confirm their existence because we do not see large amounts of high-energy radiation coming from their immediate surroundings. “Our discovery indicates that there could be many more such relics from galactic merger, and may contain a lot of hidden massive black holes still waiting to be found,” Voggel pointed out. “This could increase the total number of supermassive black holes known in the local universe by 30 percent,” she added.
Scientists expect that thanks to the Extremely Large Telescope (ELT) that ESO plans to launch later this decade in the Chilean Atacama Desert, the search for similar hidden pairs of supermassive black holes will gain additional momentum. “This detection of a pair of supermassive black holes is just the beginning,” said co-author Steffen Mieske, astronomer at ESO in Chile and Director of ESO Paranal Science Operations. “Thanks to the HARMONI instrument on the ELT, we will be able to make similar detections much further than is currently possible. ESO’s ELT will be indispensable for understanding these objects, ”he discussed.
Source: European Southern Observatory