AGN

After further research into the LRDs, Kocevski and his team confirmed that 81 percent of the subset are active galactic nuclei, or AGN, meaning they have central black holes which cause them to glow at the brightness that led to such puzzlement in the first place.

Scientists have found hints that an AGN’s brightness varies and can pulse on and off over periods lasting from 10,000 to 10 million years.

And could a galaxy have more than one AGN phase?

But in 2022 it began to show some telltale signs of an AGN.

The most likely explanation for this rapid brightening is a black hole with a mass 1 million times that of our Sun switching on an AGN at the heart of SDSS1335+0728, the team concludes.