Using Scenes effectivly

The game world of a project I am working out (space based) may need to be separated between multiple scenes. This is necessary due to the dangers of large coordinate spaces. Each scene would be a new star system (for example). The problem is, as I understand scenes they are not 'active' until loaded. So all 'life' in those scenes are pretty much dead until loaded.

I would like to create a more alive universe by having stuff go on in other star systems. Any ideas on how to approach this problem? Since this is a 2D game, could I just have the Star systems on different parts of the Z-axis rather than in new scenes?

you could do

Application.LoadLevelAdditive

or DontDestroyOnAwake

i am also building a space game my issue is also space itsself i want to be able to have multipule scenes run at the same time and not have one pause while the other runs