Relative to

The Relative to property of an object sets the reference point for the object's Distance, Position Vector, Speed, and Velocity Vector. There are two options for the Relative to property: the Simulation Origin, and the object's Orbital Parent. If the object has no Orbital Parent, the Relative to property will be automatically set to the Simulation Origin.

Location
The Relative to property can be found at the top of the Motion tab in an object's properties panel. For Galaxy objects, the Relative to property is located in the Galaxy tab, and refers specifically to the Black Hole's Relative to property. For Galaxy Nebula objects, the Relative to property is located in the Motion section of the Nebula tab.