It might be worth looking at how EVE Online does it. Essentially the star systems are massive but the only bits that actually exist are the bits that need to - generally an area of around 250km (not really modelled as km) around a player’s point of view, with everything in the player’s vicinity being ‘on-grid’. Everything outside of that ceases to exist until the player warps to a new spot, skipping over the empty space in between. The general idea is that the distances are so massive that you’re either effectively in one spot or travelling so fast that you can’t actually register any objects around you before they’re out of sight.