Planets of the DC Multiverse: Green Lantern Allies

The Guardians of Earth-One's universe deemed it necessary to remove chaotic energy from their  realm, transferring it the the parallel plane of Earth-Two (as described in All-Star Squadron Annual #1). Encased in the heart of a star of that alternate universe, it later became sentient as the Starheart. Mass within that star was the doppelgänger of the planet Oa's sun, while the star’s actual doppelgänger being the white dwarf star which the Atom of Earth-Two discovered. Since there was no planet replicated in Earth-Two's realm to compensate for the presence of Oa (and Qward of the Anti-Matter universe), it would be the Rock of Eternity that originated in Earth-S' universe that would be the center of space and time in all other universe.

Within their own dimension, the Guardians recruited a sentient planetary body named Mogo to become a Green Lantern in its own space sector. All other worlds aside from Oa also existed in other universes, and that would have included Earth-Two's own Mogo, which alas never received the ambient emerald energy kept within the Starheart. Hence it sadly remained alone in the cosmos.

One aspect of the Starheart that arrived on Earths Two and S, and perhaps other parallel planets throughout the cosmos, were meteors that crash landed in China aeons ago later known as the Green Flame of Life. This gigantic meteorite's sentient energy had a doppelgänger in the white dwarf star core that landed in Ivy Town on Earth-One, which gave the Atom his powers. And the globe that was the Starheart from which the meteorite originated, landing in China, had a parallel in the Main Power Battery located on Oa. Both were what powered Hal Jordan and Alan Scott's green lanterns.