Black Moon of Vanth

Eons ago, a miniature black hole emerged in near vicinity of Vanth. Today, no one can recall whether it was a natural quantum coincidence, a failed experiment of stupendous science, or an equally failed deployment of a planet-busting superweapon, but the black hole caused a series of cataclysms on the surface of Vanth before being contained in a powerful antigravity field by a cabal of scientists, gods, sorcerers and a time traveller. Since then, it had settled into a stable orbit, causing only a periodic visual distortion of the night sky well-known to all vanthian stargazers.
 

Black Moon rising above the North Mountains.
From here.

While the Black Moon doesn't have a true surface, there is one structure built atop of it. The Black Tower started as a simple space station housing the magical and technological apparatus necessary for maintaining the antigravity field, but has been repeatedly expanded and upgraded until its current incarnation. First, it was just the addition of new barracks for a garrison of defenders, should someone try to seize control of the antigravity field for nefarious purposes. Then a new technology stolen acquired from a crashed alien starship allowed for a mineshaft to be drilled through the event horizon of the black hole, and an explosive growth of the station begun soon after the first chunks of the extremely valuable black hole metal ore were extracted.

The station was further fortified as attacks of both space pirates and covetous civilizations grew in frequency and ferocity, until after a century of power struggles and interplanetary wars, a group of no-name psi knights calling themselves the Blackstar Order blind-sided everyone and took over the Black Tower. This Order eventually gained system-wide recognition and acknowledgement, after they withstood the onslaught of many enemies and entrenched themselves into the economy by virtue of their monopoly on black hole metal production.

While the Blackstar Order runs its black hole metal mining operation to this day, its primary interests have slowly shifted more towards politics. The crenellated duralloy bulwarks of the Black Tower no longer have to defy endless would-be conquerors, rather they serve as a secure neutral meeting ground for world leaders, gods and alien ambassadors. Or at least they served, until the recent failure of the Galactic Beacon. With interstellar travel, trade and communications suddenly severed, the Order faces an unexpected end to their routine power plays. However, with their accumulated wealth, an army of psi knights and mercenary troops, and connections throughout the whole solar system, the Order might stand to gain much from this sudden isolation, if they play their hand right.