It is stated that stopping the collapse of a red dwarf star would "save an entire galaxy from destruction". One star transforming from red to white dwarf would certainly effect its solar system, but would not have any measurable effect on an entire galaxy.
It's stated in this episode that Superman is on his way do save a galaxy that's about to be destroyed by a red dwarf star collapsing. Superman would be the last hero that should be sent as red star radiation makes Superman human.