▁layers ▁probably ▁were ▁blow n ▁away ▁by ▁the ▁super n ova ▁explos ion ▁that ▁gave ▁birth ▁to ▁the ▁black ▁hole . ▁The ▁two ▁stars ▁orbit ▁each ▁other ▁every ▁ 1 0 . 4 ▁hours ▁at ▁a ▁distance ▁of ▁roughly ▁ 2 ▁million ▁miles ▁( 3 . 2 ▁million ▁km ). ▁ ▁Spect ral ▁rad iance ▁ ▁During ▁the ▁January ▁ 2 0 – 2 1 , ▁ 1 9 9 1 , ▁out bur st ▁which ▁led ▁to ▁its ▁discovery , ▁radiation ▁was ▁produced ▁by ▁posit ron ▁anni h ilation . ▁The ▁S IG MA ▁teles cope ▁ab o ard ▁GR AN AT ▁detected ▁a ▁relatively ▁narrow ▁variable ▁emission ▁line ▁near ▁ 5 0 0 ▁ke V ▁in ▁the ▁spectrum . ▁From ▁January ▁ 9 - August ▁ 1 4 , ▁ 1 9 9 1 , ▁the ▁spectrum ▁had ▁a ▁strong ▁hard ▁component ▁extending ▁up ▁to ▁ ∼ 3 0 0 ▁ke V . ▁ ▁References ▁ ▁Harvard ▁website ▁written ▁by ▁O ros z , ▁Jer ome ▁A .; ▁B ail yn , ▁Charles ▁D .; ▁McC lin to ck , ▁Jeff rey ▁E .; ▁Rem ill ard , ▁Ron ald ▁A . ▁ ▁Category : X - ray ▁astronom y ▁Category : A stronom ical ▁X - ray ▁sources ▁Category : St ell ar ▁black ▁holes ▁Mus ca e , ▁G U ▁Category : Mus ca ▁( const ell ation ) ▁Category : K - type ▁main - sequence ▁stars <0x0A> </s> ▁The ▁Sim ono ▁were ▁an ▁ ▁ind igen ous