These Strange Red Dots In The Sky Might Be Able To Tell Us About The Earliest Black Holes In The Universe
In December 2022, NASA’s James Webb Space Telescope detected several small red objects in the sky. Scientists referred to them as “little red dots” (LRDs).
These objects have never been seen before, so experts don’t really know how they developed such unique colors or what they reveal about the early universe.
A team of astronomers put together data of the largest samples of LRDs to date. Almost all of them existed during the first billion and a half years after the Big Bang.
They found that a significant portion of the LRDs showed signs of containing supermassive black holes that are growing.
“We’re confounded by this new population of objects that Webb has found. We don’t see analogs of them at lower redshifts, which is why we haven’t seen them prior to Webb,” said Dale Kocevski, the lead author of the study from Colby College in Waterville, Maine.
“There’s a substantial amount of work being done to try to determine the nature of these little red dots and whether their light is dominated by accreting black holes.”
The team was able to gather such a large sample size because of the widely available public Webb data. They searched for the red objects in the Cosmic Evolution Early Release Science (CEERS) survey before expanding their investigation to other surveys.
Through their close examination of the data, they discovered that LRDs emerged in big groups after the Big Bang and went through a rapid decline in numbers about 1.5 billion years after the Big Bang.
Next, the team looked at the Red Unknowns: Bright Infrared Extragalactic Survey (RUBIES) for more information on some of the LRDs in their sample.
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They found that about 70 percent of the targets exhibited evidence of gas orbiting rapidly at two million miles per hour.
This was a sign of an accretion disk around a supermassive black hole. The findings suggest that many LRDs are just accreting black holes, also known as active galactic nuclei (AGN).
“The most exciting thing for me is the redshift distributions. These really red, high-redshift sources basically stop existing at a certain point after the Big Bang,” said Steven Finkelstein, a co-author of the study at the University of Texas at Austin.
“If they are growing black holes, and we think at least 70 percent of them are, this hints at an era of obscured black hole growth in the early universe.”
There is a lot about LRDs that is still up for debate among the scientific community. More work needs to be done to fully understand their nature, such as examining their mid-infrared properties and seeing how many accreting black holes in the universe fit the criteria of LRDs.
The results of the study were posted to the arXiv preprint server.
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