The abyss.
Contrary to its name, it wasn't a specific place within the universe. It was just a generalized name for the highest tier of prisons developed by the hegemons for a very specific group of people.
For those who committed crimes but felt no remorse whatsoever.
One could find themselves in the abyss for something as small as snatching groceries on a regular basis, something average like bullying, big crimes like rapes and murders all the way to high crimes like treason or espionage.
Because in essence, it was wrong to call the abyss a prison. Calling it a resocialization center was more on the point.
On their own, abyss locations appeared like your average self-sufficient stations floating in space while maintaining only minimal contact with the rest of the universe. And even that was just to ensure its operations were going smoothly.
