Originally Posted by Darth Credence
Not a binary system. It didn't drain a star entirely for one shot, both its shots were needed to drain the star (and it didn't get the second one off).
Originally Posted by Daimbert
Spoiler: Why they built it there
Starkiller Base was built into the planet Ilum, which was one of the biggest sources for kyber crystals and the Jedi's most sacred planet. The Empire stripped it, among other planets, for crystlas for the Death Star, and created the enormous trench, and also left behind a large amount of infrastructure and technology.