high energy radiation stellar environment ref name gudel current wisdom massive coronal main sequence stars late early f stars conjecture supported observation theory ref name gudel young low mass stars cluster newly formed stars orion nebula newly formed stars known pre main sequence stars stage stellar evolution reach main sequence stars stage ages million years produce x rays stellar coronae however x ray emission sup sup sup sup times stronger main sequence stars similar masses ref name preibisch ref x ray
Natural science Space science Astronomy X-ray astronomy