Little Red Dots Lead To Big Discoveries

Names are a strange thing in astronomy. Sometimes scientists come up with grandiose, simple name, like the Extremely Large Telescope. Other times, they come up with unique sounding names, like quasars. And sometimes they come up with names that, while descriptive in some sense, are completely misleading in others. That is the case for Little Red Dots (LRD) - active galactic nuclei in the early universe that show up as a little red dot in the images captured by whatever telescope found them. However, they actually represent supermassive black holes hundreds of millions of times the size of our Sun. A new paper from Federica Loiacono and her colleagues at Istituto Nazionale di Astrofisica in Italy describes one of these behemoths they found with the James Webb Space Telescope at a period of the early universe, about 11 billion years ago, known as the “cosmic noon”.

Cosmic noon, the period from 10-11 billion years ago, is thought by astronomers to be one of the most active periods in the history of the universe. Stars were being formed and black holes were eating matter at a rate not matched either before or since. Finding LRDs during this period will provide key insights into how supermassive black holes formed during this time, potentially providing insights into the further evolution of the universe from then on.

Dr. Loiacono and her team did find one of those, and, in another interesting naming decision, they decided to call this latest LRD the Big Red Dot (BiRD). That’s not because it’s bigger than other LRDs found in the same epoch of time, but because it’s brighter than all other LRDs found so far. Given that there’s been several hundred, that is a pretty impressive feature for this one particular discovery.

BiRD was discovered using the James Webb Space Telescope’s Emission-Line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER) survey, which was specifically designed to check out the areas around six notable quasars, including SDSS J1030+0524, the one that BiRD was found near.

One of the most striking features of BiRD is that it is blasting out helium gas at a rate of 830 km/s. That fast-moving gas creates an absorption line in the data by blocking out some of the light the researchers expected to see there.

Strangely, it is also relatively quiet in two other spectra where LRDs are normally very active - X-rays and radio. The authors offer up two theories for why BiRD might be quiet in the X-ray spectrum. First, it might be blocked by a thick cloud of gas that is essentially dust-free, which, while possible, would be much more all-encompassing of the black hole than other examples. Alternatively, BiRD’s black hole could be eating matter much faster than normal rates, causing a thick disk of material to form around it, blocking the light. The lack of radio waves is harder to explain, though undoubtedly the authors have some theories that just didn’t make it into the paper.

Another important feature of BiRD is that it is very similar to two other LRDs found in the same period of universal evolution. The “Rosetta Stone” and the RUBIES-BLAGN-1 LRDs represent the extremes of astronomical naming conventions, as well as have similar properties to BiRD. They have similarly strong helium gas outflows, and are conventionally the same expected size as BiRD, despite its name.

As JWST and other, even more powerful telescopes come online, we will undoubtedly find more of these Little Red Dots, and therefore begin to piece together how the universe was back when it was a “teenager”. It will take some more time to determine whether BiRD will stand out from its peers, or whether it is representative of a great mass of as-yet-undiscovered black holes. Either way will be good news for the future of astronomy.

Learn More:

F. Loiacono et al - A big red dot at cosmic noon

UT - New Insights Into Little Red Dots. An Early Phase of Black Hole Growth

UT - Webb Provides an Explanation for "Little Red Dots"

UT - Little Red Dots in Webb Photos Turned Out to Be Quasars