Ten billion years ago, strange scarlet sparks already shone in the Universe. The JWST telescope spotted their light, which had reddened due to the expansion of space — scientists call this redshift. The dots were tiny yet as bright as whole galactic evolution. They were dubbed 'little red dots' and for a long time no one could figure out what they were. The answer came from an old theory about how matter falls into a black hole. If there's too much gas, the hole can't handle it — it starts to boil. A Accretion disk of hot gas forms around the hole, but when the flow is too strong, the excess gas is hurled away. This outburst works like a boiling cauldron: the gas heats up to thousands of degrees, becomes a plasma cloud, and hides the hole from our eyes. We see only this cloud, and its light is red.

Red light appears at temperatures between three and six thousand degrees. That's exactly the temperature given by a model built back in the 1970s by Nikolai Shakura and Rashid Alievich Sunyaev to describe 'overfed' black holes. Later, astronomers spread the dots' light into a spectroscopy rainbow and saw the characteristic patterns of hydrogen — confirming that we're looking at hot material flying outward. Nearly a century ago, scientist Arthur Eddington calculated the maximum brightness for any cosmic body, and the red dots shine right at that limit.

Now, by studying these dots with numerical simulation and new data from JWST, astronomers hope to understand how active galactic nucleus affected their hosts. Over time, as the chemical composition of the gas (its metallicity) changed, so did the hole's boiling. In this way, red dots help us read the growth history of the entire Universe.