The growth of galaxies seems to be tied to the growth of supermassive black holes, and vice-versa. Extragalactic space is relatively crowded, and galaxies are often pulled together by the mutual gravitational attraction of their (mostly dark) matter. As galaxies collide and merge, the supermassive black holes they contain may eventually spiral together, rocking the Universe with a burst of gravitational waves, and leaving behind an even more super-massive black hole as a result. A new study helps show how this might happen in triple-galaxy mergers. Such triple mergers are thought to be important in the cosmic scheme of things since studies show that supermassive black hole mergers are more frequent in triple systems because the presence of a third black hole can help drive the merger of the other two. The image above shows X-ray images from the Chandra X-ray Observatory (on the left) and optical images (right) of two triple mergers, J1027 and J1708. The circled sources show the locations of X-ray bright, actively feeding supermassive black holes remaining in these two triple mergers. Seven such merging systems were studied, and they showed a variety of properties. One system showed evidence of a single accreting supermassive black hole; one showed the presence of three supermassive black holes; four systems contained two accreting supermassive black holes; and one merger showed no evidence of a supermassive black hole at all - which means that any leftover black holes there are not actively feeding on the gas and dust in the merged galaxy, orperhaps the merged supermassive black hole was flung out of the galaxy, and is now hurtling, unseen, through space.
X-ray: NASA/CXC/Univ. of Michigan/A. Foord et al.;
Optical: SDSS & NASA/STScI
A new study helps reveal what happens to supermassive black holes when three galaxies merge, as reported in our latest press release. This result, which used data from NASA's Chandra X-ray Observatory and several other telescopes, tells astronomers more about how galaxies and the giant black holes in their centers grow over cosmic time.
While there have been previous studies of mergers between two galaxies, this is one of the first to systematically look at the consequences for supermassive black holes when three galaxies come together. This panel of images contains data from two of seven galactic collisions in the new study containing two supermassive black holes left growing after the collision. The pair of mergers are seen in X-rays from Chandra (left in purple) and optical data (right) from NASA's Hubble Space Telescope and the Sloan Digital Sky Survey (SDSS). Circles in a labeled version of the Chandra image show X-rays from hot gas falling towards each black hole.
These triple galaxy mergers were first identified by sifting through data from the SDSS and NASA's WISE mission and then comparing the results to X-ray data in the Chandra archive. This method identified seven triple galaxy mergers located between 370 million and one billion light years from Earth.
AGN Triality of Triple Mergers: Detection of Faint X-ray Point Sources ~ Adi Foord et al