A Prior arrived on Kallana, rid himself of the Jaffa population and initiated an Ori forcefield which eventually engulfed the entire planet. Once this was done, the force field shrank the mass of Kallana until the world had become a singularity, designed specifically for powering the Supergate indefinitely.
The Supergate was destroyed before it was able to be activated, but Kallana was lost.
HOME TO - Destroyed
FIRST APPEARED - Beachhead
Beachhead - SG-1 arrives on Kallana with a Mark IX Gate Buster to destroy the Ori force field, but instead the weapon grows the field and eventually engulfs and destroys the planet.
Ripple Effect - The black hole that was once Kallana is the focal point for a break down of the metaverse when more than 65 alternate realities collide.