Amphion

From Memory Alpha, the free Star Trek reference

Amphion was a previously dead star in the antimatter universe that was the counterpart to the star Beta Niobe in our universe.

In 2269, Karla Five, who was investigating the dead star, got caught unaware as Amphion went supernova and came back to life and pulled her ship into the star. Instead of burning up, she passed through the Beta Niobe nova, into a universe where everything operates in reverse to her universe. She hypothesized that two stars going nova at the same time in both universes creates a gateway, through which her ship passed, and eventually returned through. (TAS: "The Counter-Clock Incident")