Just like our Milky Way Galaxy, there’s a large hole at the centre of other galaxies at well. Sometimes, these galaxies can collide with each other in the vast expanse of our universe. So, what happens to these galactic centres i.e., black holes when such a collision occurs? Well, they start to grow, rapidly.
According to NASA, as the galaxies collide and material start to fall toward the giant black holes, they get heated to over millions of degrees and produce X-rays. The discovery was made possible with the help of NASA's Chandra X-ray Observatory in addition to multiple other telescope facilities.
While there have been some studies about two galaxies merging and their subsequent impact on black holes before, a triple merger had largely been unobserved. In the newest study, Adi Foord of Stanford University, and her team looked particularly at collisions among three galaxies.
Using NASA's WISE mission and the Sloan Digital Sky Survey (SDSS) and the Chandra archive, the team located a whopping seven different triple galaxy mergers. They are all between 370 million and one billion light-years from Earth.
With the help of targeting systems, they detected the source of X-rays in each, which would identify the position of the black hole. X-ray images are hard to track as they give faint results, so special software was developed to allow for proper imaging. Additionally, they used data from other telescopes to confirm the X-ray was indeed coming from a black hole and not some unidentifiable source.
The result, the team discovered slightly different processes in each of the seven triple galaxy mergers. One of them has a single, supermassive, growing black hole. Four have double growing supermassive black holes. And the last has a triple growing supermassive black hole. One of the systems did not yield any result as no X-ray could be detected from any supermassive black holes.
The systems that had multiple black holes have around 10,000 and 30,000 light-years between them. Researchers claim these results are important as it may shed some light onto how black holes grow in the galaxies they inhabit.
Data from Chandra and WISE showS that when a supermassive black hole is growing, it has the largest amount of dust and gas. The observation is identical to the computer simulations about mergers. The theoretical simulations had suggested, “higher levels of gas near black holes are more likely to trigger rapid growth of the black holes.”
The scientists can study these triple mergers to understand a phenomenon called gravitational waves. They want to assess if the multiple supermassive black holes can approach so close to each other that they make ripples in spacetime. The energy released during gravitational waves must cause the black holes to merge as well.
Previous data from other space observation centres (ex LIGO in Europe) has suggested stellar-mass black holes can create gravitational waves and merge. However, it is not known is supermassive black holes can do the same.