After the Battle of P3Y-229, the Ori were free to come into the Milky Way galaxy as they pleased. In an effort to stop them from sending any more ships into the Milky Way galaxy, a plan was devised by the Tau'ri, which led them to the Pegasus galaxy.
After delivering supplies to Atlantis and dropping off Dr. Daniel Jackson and Vala Mal Doran to search the Atlantis database for Merlin’s weapon, Lt. Colonel Cameron Mitchell and Lt. Colonel Samantha Carter accompanied by the Atlantis expedition's chief science officer, Dr. Meredith Rodney McKay set out on the Odyssey for a black hole. (SG1: "The Pegasus Project")
The Odyssey orbited a black hole in the Pegasus galaxy in order to connect a wormhole to the Supergate in the Milky Way galaxy using a jump between a Stargate in Pegasus released near the black hole by the Odyssey and a Stargate next to the Supergate released by Teal'c in an Al'kesh using Nuclear warheads. After the wormhole was connected between the two gates the first two attempts failed, but the nuclear detonations drew a Wraith Hive ship to the Odyssey's position.
The Hive ship engaged the Odyssey in battle and caused the Odyssey's' hyperdrive to go down. The Odyssey was at a disadvantage due to the black hole interfering with its systems and the gravity well as well, so the Odyssey drew the Hive ship in closer while pulling a slingshot maneuver. The Hive ship's systems, including its jamming field, were affected by the black hole and Odyssey beamed the last two nukes on board when it was next to the active Stargate. The Hive ship was destroyed and the blast caused the wormhole to jump to the Supergate on the other end, destroying an Ori warship in the unstable vortex of the Supergate which had been drawn in by Teal'c piloting the Al'kesh. (SG1: "The Pegasus Project")