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
"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
Everything within this core zone is a high security zone where travel is restricted due to the black hole and other shifting gravitational anomalies.
This black hole near Tython is the galactic core black hole mentioned in this answer.