You needed to wait for the boss star to appear, it drops a core on death. Once you collect 10, you win.
Viewing post in The Heaviest Matter of the Universe jam comments
I saw in the description that there are “boss stars” that are supposed to appear every minute, but i never encountered anything that looked like it might be a boss. Do i need to survive longer than three min to get the first? Is there a specific space they spawn in that i might have been too far away from?