Hmm... I see where the other answerers are going with this (and I agree, this is more of a graphic design and layout issue). But I disagree that that answer is to distribute things to close up that space, or make things larger to minimize the space.
"White space" is a perfectly valid - and actually quite valuable - design element, and its power should not be underestimated. You can look into the full Gestalt principles of design to learn why... here are a couple of resources:
Blank space plays a strong factor in several of the Gestalt aspects of visual design, but I think in your case we are mostly dealing with issues of proximity and similarity.
So what I'm understanding is that you want the large star to remain discrete and to stand out from the other stars, and you are perfectly appropriately using space/proximity and similarity/difference principle to help that along. But you want a way to make that space itself more interesting, without minimizing it - do I have that right?
This definitely falls into the category of visual and/or motion design, but you could certainly use some sort of interesting background or moving animation field to keep that space more "alive." You want it to be subtle enough that it doesn't interfere with the main action, of course, but generations of arcade games have used such things for this very reason, from Galaga's animated star fields or Super Mario's clouds and plants, to the gorgeous, atmospheric backgrounds of Monument Valley (already a gorgeous game), or any number of newer games with large playfields but a lot of space:
All of those background elements and scenery are strictly ornamental and do nothing to enhance the actual interactions of the games, but they increase the atmosphere and aesthetic value greatly, and in some cases can help to make a good game great.
I can easily envision the exact screen you have there, but with a subtly animated abstract texture in the background, or some interesting (and again subtle) geometric pattern... the animations or patterns could change depending on the level the user is on.
Most importantly, however, is that an ornamental element should never interfere with the interactive elements or detract in any way from the game play value! You will need to experiment and play test on these new factors as well to make sure they are not having any undesired affect on the playability of your game.