▁astronom y ▁High - mass ▁X - ray ▁bin aries ▁( H M X B s ) ▁are ▁composed ▁of ▁O B ▁super gi ant ▁companion ▁stars ▁and ▁compact ▁objects , ▁usually ▁neut ron ▁stars ▁( NS ) ▁or ▁black ▁holes ▁( B H ). ▁Super gi ant ▁X - ray ▁bin aries ▁( SG X B s ) ▁are ▁H M X B s ▁in ▁which ▁the ▁compact ▁objects ▁orbit ▁massive ▁compan ions ▁with ▁orb ital ▁periods ▁of ▁a ▁few ▁days ▁( 3 – 1 5 ▁d ), ▁and ▁in ▁circular ▁( or ▁slightly ▁ecc ent ric ) ▁or bits . ▁S G X B s ▁show ▁typical ▁the ▁hard ▁X - ray ▁spect ra ▁of ▁acc re ting ▁p uls ars ▁and ▁most ▁show ▁strong ▁absor ption ▁as ▁obsc ured ▁H M X B s . ▁X - ray ▁lum inos ity ▁( L x ) ▁increases ▁up ▁to ▁ 1 0 3 6 ▁erg · s − 1 ▁( 1 0 2 9 ▁w att s ). ▁ ▁The ▁mechanism ▁trigger ing ▁the ▁different ▁temporal ▁behavior ▁observed ▁between ▁the ▁classical ▁S G X B s ▁and ▁the ▁recently ▁discovered ▁super gi ant ▁fast ▁X - ray ▁trans ients ▁( SF XT ) s ▁is ▁still ▁deb ated . ▁ ▁St ell ar ▁X - ray ▁astronom y ▁St ell ar ▁X - ray ▁astronom y ▁is ▁said ▁to ▁have ▁started ▁on ▁April ▁ 5 , ▁ 1 9 7 4 , ▁with ▁the ▁detection ▁of ▁X - ray s ▁from