▁Observ ations ▁are ▁reve aling ▁a ▁growing ▁number ▁of ▁rec urrent ▁X - ray ▁trans ients , ▁character ized ▁by ▁short ▁out bur st s ▁with ▁very ▁fast ▁rise ▁times ▁( t ens ▁of ▁minutes ) ▁and ▁typical ▁dur ations ▁of ▁a ▁few ▁hours ▁that ▁are ▁associated ▁with ▁O B ▁super gi ants ▁and ▁hence ▁define ▁a ▁new ▁class ▁of ▁massive ▁X - ray ▁bin aries : ▁Super gi ant ▁Fast ▁X - ray ▁Trans ients ▁( SF XT s ). ▁Observ ations ▁made ▁by ▁Ch andra ▁indicate ▁the ▁presence ▁of ▁loops ▁and ▁rings ▁in ▁the ▁hot ▁X - ray ▁em itting ▁gas ▁that ▁surr ounds ▁Mess ier ▁ 8 7 . ▁A ▁magnet ar ▁is ▁a ▁type ▁of ▁neut ron ▁star ▁with ▁an ▁extremely ▁powerful ▁magnetic ▁field , ▁the ▁decay ▁of ▁which ▁powers ▁the ▁emission ▁of ▁cop ious ▁amounts ▁of ▁high - energy ▁elect romagnet ic ▁radiation , ▁particularly ▁X - ray s ▁and ▁g amma ▁ray s . ▁ ▁X - ray ▁dark ▁stars ▁ ▁During ▁the ▁solar ▁cycle , ▁as ▁shown ▁in ▁the ▁sequence ▁of ▁images ▁at ▁right , ▁at ▁times ▁the ▁Sun ▁is ▁almost ▁X - ray ▁dark , ▁almost ▁an ▁X - ray ▁variable . ▁Bet el ge use , ▁on ▁the ▁other ▁hand , ▁appears ▁to ▁be ▁always ▁X - ray ▁dark . ▁Hard ly ▁any ▁X - ray s ▁are ▁em itted ▁by ▁red ▁gi ants . ▁There ▁is ▁a ▁rather ▁ab rupt ▁on set ▁of ▁X - ray ▁emission ▁around ▁spectral ▁type ▁A 7 -