It is believed* to actually be artificial, specifically its a ringworld built by a bunch of overachievers who didn't think making it merely the size of a star system was remotely enough. That's also why you can't see any stars it in, just one gigantic glow from the center. Having multiple stars was annoying and messed with their day/night cycle so they glued them all together into one supermassive sun in the middle that would illuminate the ringworld more evenly.
*Source: This doodle I made on a napkin.