Milky Way Center
This addon adds to Celestia famous black holes and most real stars (catalogs E, N, B, GCIRS and partially S added) of the Milky Way center.
Some stars have real orbits, and some are still stable because their orbital period is unknown.
Some stars have their own characteristics (double star systems or accretion discs in Be stars)
The addon radially modifies black holes (especially Sagittarius A *), transforming them from something outdated and incomprehensible into really dangerous objects.
It is also worth noting that the add-ons as shown by various tests with such aggressive accretion discs work without brakes.
How to install add-ons? Find out here.