Shortly after NASA's James Webb Space Telescope began its science observations, astronomers reported a new class of mysterious compact, red objects located roughly 12 billion light-years from Earth or farther. Many scientists believe LRDs are supermassive black holes embedded in dense clouds of gas that mask the typical signatures - including X-rays - that astronomers normally use to identify growing black holes. This makes them distinct from typical growing supermassive black holes, which are not shrouded in dense gas, allowing bright ultraviolet light and X-rays from material orbiting the black holes to escape freely. Because of these characteristics and their potential similarities to stellar atmospheres, researchers have described this as the "black hole star" scenario for LRDs.
The newly identified X-ray dot, officially designated 3DHST-AEGIS-12014 and located about 11.8 billion light-years from Earth, may provide a crucial bridge between black hole stars and typical growing supermassive black holes. It displays most of the hallmarks of an LRD - being small, red, and at a vast cosmological distance - but unlike other known LRDs, it emits detectable X-ray light.
"Astronomers have been trying to figure out what little red dots are for several years," said lead author Raphael Hviding of the Max Planck Institute for Astronomy in Germany. "This single X-ray object may be - to use a phrase - what lets us connect all of the dots."
The team found this exceptional object by comparing new data from Webb with a deep survey previously carried out by Chandra. "If little red dots are rapidly growing supermassive black holes, why do they not give off X-rays like other such black holes?" said co-author Anna de Graaff of the Center for Astrophysics at Harvard and Smithsonian, in Cambridge, Massachusetts. "Finding a little red dot that looks different from the others gives us important new insight into what could power them."
The researchers propose that the X-ray dot represents a transition phase between an LRD and a typical growing supermassive black hole. As the black hole star consumes its surrounding gas, patchy holes form in the gas clouds, allowing X-rays from infalling material to escape and be detected by Chandra. Eventually all the surrounding gas is consumed and the black hole star phase ends entirely.
Additional hints in the Chandra data suggest variations in X-ray brightness, which supports the partial-obscuration interpretation. As the rotating gas cloud moves patches of denser and less dense material across the line of sight to the black hole, the observed X-ray brightness fluctuates accordingly.
"If we confirm the X-ray dot as a little red dot in transition, not only would it be the first of its kind, but we may be seeing into the heart of a little red dot for the first time," said co-author Hanpu Liu of Princeton University in New Jersey. "We would also have the strongest piece of evidence yet that the growth of supermassive black holes is at the center of some, if not all, of the little red dot population."
An alternative explanation is that the X-ray dot is a more common type of growing supermassive black hole obscured by an exotic variety of dust not previously observed by astronomers. Future observing campaigns are planned to distinguish between these possibilities.
"The X-ray dot had been sitting in our Chandra survey data for over ten years, but we had no idea how remarkable it was before Webb came along to observe the field," said co-author Andy Goulding of Princeton. "This is a powerful example of collaboration between two great observatories."
Related Links
NASA Chandra X-ray Observatory
Understanding Time and Space
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
