The Cormoran Supermassive Black hole, in NGC 6183, is surrounded by an alien civilisation.
A supermassive black hole (SMBH) is the largest type of black hole, on the order of hundreds of thousands to billions of solar masses. SMBHs are found in the centre of almost all large galaxies; some have more than one such object, although these will almost certainly merge at some point in the future.
In the core of the Milky Way galaxy, Sagittarius A* is a SMBH with a mass of 4.3 million solar masses, slightly small compared to others in comparable galaxies. Telescopic observations by the Argus Array and similar systems have found that galactic supermassive black holes are often the site of considerable actiity by xenosophont civilisations, and are sometimes surrounded by various kinds of megastructure or other remnants of intelligent construction. The Cormoran SMBH for instance is embedded in a large artificial accretion disk which provides light and heat for a large swarm of planets.