At the end of the first part, the hero merges with a sentient star to stop it from going nova. His friend (an alien) along with the assassin (that tries to kill him in the start) also get sucked into this merger. All of them merge with the star and prevent it from going nova. In the end they create a sort of wormhole/bridge through space-time.
The second part is about a vessel traveling through this bridge and facing a threat from bat-like aliens that pull passengers into the void while in hyper/metaspace. The protagonist is a little girl. There is a robot common to both these stories.
It is not the Starchild trilogy or Whipping Star by Frank Herbert.