What is the symbolic role of the Green Sun in the narrator's visions?

The Green Sun initially appears to the narrator as a 'single, great star, of vivid green' [1] that grows to 'vast proportions' [1], filling 'all the sky' [1]. It is described as a 'huge emerald, scintillating rays of fire across the world' [1], and its light is so tremendous that it appears to fill the sky with 'quivering flames' [1].

Symbolically, the narrator speculates that this 'stupendous globe of green fire might not be the vast Central Sun—the great sun, 'round which our universe and countless others revolve' [1]. He also questions if 'the dead stars make the Green Sun their grave' [1] and if it is 'the abode of some vast Intelligence' [1]. It represents a source of ultimate light and a potential cosmic center at the end of all things.

Space: The House On The Borderland