Legends Answer:

I only know of 2 books that mention them, *Star Wars: Into the Void* and *Darth Bane: Rule of two*.

In *Star Wars: Into the Void* the protagonists are trying to stop the antagonist from activating an ancient Gree device that would create a black hole,

>It could destroy Tython," Dam-Powl said. "Exposing dark matter to normal matter would be cataclysmic. It would create a **black hole**, swallowing Tython in a heartbeat. The rest of the system, too."

>*Star Wars: Into the Void* page 16,   25 793 BBY

and
>"He's going to kill everyone, " seh said. "Once he initiates the device, the dark matter will form a **black hole** and everyone in the system-"

>*Star Wars: Into the Void* page 185,   25 793 BBY



In the *Darth Bane series* they are searching for an ancient temple located on Tython (though 20 000+ years *after Into the Void*) which is near a black hole.

>"Tython?" Zannah exclaimed, recognizing the name. "Isn't that one of the Deep Core worlds?"

>The Deep Core was a small cluster of densely packed stars centered on a **black hole** in the very heart of the galaxy.

>*Darth Bane: Rule of two* Page ???, ~1000 BBY

This black hole near Tython is the glactic core black hole mentioned in [this][1] answer.


  [1]: http://scifi.stackexchange.com/questions/47830/is-there-a-supermassive-black-hole-at-the-galactic-core