How Astronomers Are Searching For Hidden Supermassive Black Holes – SlashGear

To find the hidden black holes, the researchers focused on supermassive black holes. These are a particularly large type of black hole that are found most often at the centers of galaxies. It is thought that almost all large galaxies have a supermassive black hole, but some of these have yet to be observed. In this project, the researchers compared galaxies that were bright X-ray sources but dim in visible light, which are called “XBONGs” (X-ray bright, optically normal galaxies). They were able to identify 817 of these XBONGs that shone brightly in Chandra’s X-ray data but not in the Sloan survey data.

When they looked at these XBONGs, they found that around half of them were glowing in the X-ray wavelength due to previously undetected supermassive black holes. These black holes were busy feeding on nearby material, so they were giving off radiation, but most of that energy in the visible light wavelengths was hidden by thick clouds of dust and gas. X-rays can more easily pass through these shrouds, so they can be detected even when visible light can’t be.

The researchers knew that they were looking at supermassive black holes and not other types of objects because the X-rays they were giving off were so bright, they must have been coming from supermassive black holes which are feeding and growing quickly. “It’s not every day that you can say you discovered a black hole,” said another of the researchers, Alyssa Cassity of the University of British Columbia, “so, it’s very exciting to realize that we have discovered hundreds of them.”