Oa is one of the oldest planets in the DCU. It is the home and headquarters of the Guardians of the Universe, an alien race of blue-skinned, white-haired scientifically powerful humanoids. These aliens have evolved from a planet called Maltus. The Guardians administer their brand of policing the Universe by creating champions know as the Green Lantern Corps, a group of powerful universal police officers. Each member of the Green Lantern Corps is equipped by the Guardians with Green Power Rings and a Green Lantern Power Battery with which to charge the rings. Oa was chosen to be the headquarters of the universe, because it is said by the Guardians that it lies in the center of the universe if we imagine the universe as a sphere. This sphere is divided equally into segments all leading to Oa and those are the patrolling sectors of the Green Lantern Corps.
Oa appears to have no indigenous life. The plant of Oa's only features are what the Guardians have created on its surface.
During Emerald Twilight story arc, the Guardians of the Universe sacrificed themselves to create one final power ring. This power ring is extremely powerful and may be the strongest power ring held by a Green Lantern. This Power Ring was given to the "Torch-bearer" Kyle Rayner. The legendary Green Lantern Corps member Hal Jordan, the Green Lantern of sector 2814, who has now gone rogue under the influence of the evil entity Parallax, killed all but one of the Guardians, Ganthet, and most of the Corps before draining Oa's Central Power Battery of its energy. The planet is later destroyed during a battle between Jordan and his successor, Green Lantern Kyle Rayner.
What was the remains of the planet Oa served as a base of operations for the villain Oblivion during the Circle of Fire story arc.
In the graphic novel Legacy: The Last Will and Testament of Hal Jordan Oa is rebuilt as the final wish of Hal Jordan's former power ring. The Central Battery is recharged and the now resurrected Guardians promote Kyle Rayner to the near-omnipotent Ion, solidifying him as the Torch-Bearer and a key element to Oa.
The Guardians later decide that the Green Lantern Corps is not enough protection for the plant Oa. Now fortified by creating a planet-wide armor and defensive system to prevent attacks, Oa can defend itself. The outer shell is eventually destroyed by the Scarred Guardian in order to make Oa vulnerable for the coming of Blackest Night.
In the 31st Century Oa is a barren wasteland with only one Green Lantern, Rond Vidar, and one Guardian, Sodam Yat, remaining. When Rond Vidar is killed during the events of Legion of 3 Worlds, a downtrodden Yat believes this is the end of the Corps because he has not been able to recreate the Green Lantern Corps for a long time. Eventually he regains the Willpower to restart the Corps, reigniting the Central Power Battery and sending the inert rings out into the universe to find suitable bearers.
When the villain Relic used his collectors to drain and destroy the Central Power Battery, a chain reaction was triggered through Oa's core, obliterating the planet.
Green Lanterns Corps Headquarters
Meeting Hall: Large meeting area for roll call, assignments, briefings and general meetings.
Inner Sanctuary: A large room where the Guardians of the Universe reside. It is often locked and the Guardians refuse to see anyone they do not specifically call on. The inside of the sanctuary itself is an empty void that projects all of space, allowing the Guardians to view the status of the universe from inside their sanctuary.
Central Power Battery: The central feature of Oa. It contains the energy that all Green Lantern Rings use to power their rings.
The Foundry: Subterranean foundry where Power Rings and Batteries are forged from pure Willpower.
Hazard Simulation Facility:This is a training ground. Drill Sergeant Kilowog trains rookies to help them understand how to wield their new power rings.
Dining Hall: The central eating location on Oa. To maintain and sustain any Green Lantern's nutritional needs there is an executive chef, Greet, who specializes in replicating dishes from across the universe.
Hall of Great Service: The hall of great service works as a library and safehouse for the recorded stories and deeds of the finest Green Lanterns of all time. These stories and deeds are recorded in the Book of Oa, which serves as the law book.
Sector Houses: Sector Houses work as remote jail-houses used to hold criminals as they await escort back to the Oan Sciencells. These safe-houses serve as sector headquarters for the sector Lanterns.
The Sciencells: Are the jailing system of the Green Lantern Corps.
Memorial Hall: A Green Lantern named Morro, and his pet Dratures, are the crypt keepers to the Memorial Hall. Many Lanterns have dies in the line of duty and to honor fallen Green Lanterns they have a statue erected in their memory.
Guy's Place or "The Big W":Was a restaurant owned by Guy Gardner and Kyle Rayner, serving Earth's American foods and beverages. Guy Gardner wanted to re-establish this once proud brand of American Fast Food to his fellow Green Lantern Corps and new residence on Oa. The restaurant is eventually wrecked during the Emerald Eclipse arc.