Problems with the book and movie
Even though Kurt Vonnegut loved the adaptation to the movie, it seems pretty clear that Billy Pilgrim's life on Tralfamadore is an illusion and/or coping mechanism Billy has with his life, due to his PTSD from the war and living with a fat, annoying wife. But in the movie, it seems pretty real because Montana Wildhack just disappeared or vanished when someone was with her (the story she tells Billy after meeting him).
Off the subject, I would assume Tralfamadore is just a moon of Jupiter or just a poor choice of FX. The light years from Earth to them is either sloppy arithmetic or their metric system is different