Solid entry with some of the best pacing I've seen so far. I think this is a great example of a jam game: short, shows off the core concepts and its future potential, and leaves you wanting a full version.
The game starts off interesting enough - the visuals are engaging and you immediately get the sense of a growth game (like agar.io). Idle play quickly became the ideal way to play for me, so afterwards it turned into more of a standard idle game. Being able to upgrade things such as particle count and gravity pull were great uses of the core mechanics.
The unfolding hits fast, which again, is great for a jam game and really pulled me along. Things start moving fairly quickly after the 5th protostar or so. At that point, it seemed like you opted for upgrades via milestones more so than opting in. While convenient and idle-friendly, that swayed it pretty far towards the idle end and I mostly ended up just checking in on it every once in a while since it didn't really need my input.
Watching the universe light up over time + the bottom bar filling up is a great touch. This is a good concept overall and the part I liked best was how you could divide up work between your protostars to achieve different goals simultaneously. Definitely something worth exploring more if you do a full version.