▁produced ▁an ▁expand ing ▁wave ▁of ▁star ▁production ▁( sh own ▁as ▁bright ▁blue ) ▁travel ing ▁at ▁an ▁effective ▁speed ▁of ▁ <0xE2> <0x89> <0xB3> 1 0 0   km ▁s − 1 ▁and ▁began ▁some ▁ 4 0 ▁million ▁years ▁ago . ▁The ▁most ▁extreme ▁period ▁of ▁star ▁formation ▁is ▁estimated ▁to ▁have ▁ended ▁ 1 5 ▁million ▁years ▁ago ▁and ▁as ▁the ▁young , ▁super ▁hot ▁stars ▁died ▁( as ▁expl oding ▁super nov as ) ▁they ▁left ▁behind ▁neut ron ▁stars ▁and ▁black ▁holes . ▁ ▁The ▁right - side ▁galax y ▁is ▁ 3 0 , 0 0 0 ▁light ▁years ▁in ▁diameter ▁and ▁is ▁located ▁ 2 1 , 0 0 0 ▁light ▁years ▁away ▁from ▁its ▁partner ▁galax y . ▁The ▁entire ▁system ▁extends ▁some ▁ 1 1 5 , 0 0 0 ▁light ▁years ▁across . ▁ ▁In ▁September ▁ 2 0 0 8 , ▁Hub ble ' s ▁main ▁data - hand ling ▁unit ▁failed . ▁After ▁the ▁problem ▁was ▁corrected , ▁the ▁teles cope ' s ▁W ide ▁Field ▁Planet ary ▁Camera ▁ 2 ▁was ▁aim ed ▁at ▁Ar p ▁ 1 4 7 ▁and ▁the ▁quality ▁of ▁the ▁images ▁taken ▁assured ▁NASA ▁that ▁Hub ble ▁was ▁working ▁properly . ▁ ▁Main ▁ring ▁The ▁main ▁ring ▁contains ▁nine ▁bright ▁X - ray ▁sources ▁which ▁are ▁black ▁holes , ▁each ▁with ▁a ▁mass ▁ 1 0 – 2 0 ▁times ▁the ▁mass ▁of ▁the ▁Sun . ▁The ▁edge - to - edge ▁expansion ▁of