▁for ▁a ▁long ▁time . ▁Phys ical ▁theory ▁changes ▁with ▁time . ▁With ▁respect ▁to ▁cel est ial ▁X - ray ▁sources , ▁X - ray ▁ast ro physics ▁tends ▁to ▁focus ▁on ▁the ▁physical ▁reason ▁for ▁X - ray ▁bright ness , ▁whereas ▁X - ray ▁astronom y ▁tends ▁to ▁focus ▁on ▁their ▁classification , ▁order ▁of ▁discovery , ▁vari ability , ▁resol v ability , ▁and ▁their ▁relationship ▁with ▁nearby ▁sources ▁in ▁other ▁const ell ations . ▁ ▁Within ▁the ▁const ell ations ▁Or ion ▁and ▁Er id anus ▁and ▁stretch ing ▁across ▁them ▁is ▁a ▁soft ▁X - ray ▁" hot ▁spot " ▁known ▁as ▁the ▁Or ion - Er id anus ▁Super b ubble , ▁the ▁Er id anus ▁So ft ▁X - ray ▁En h ancement , ▁or ▁simply ▁the ▁Er id anus ▁B ubble , ▁a ▁ 2 5 ° ▁area ▁of ▁inter lock ing ▁ar cs ▁of ▁H α ▁em itting ▁fil aments . ▁So ft ▁X - ray s ▁are ▁em itted ▁by ▁hot ▁gas ▁( T ▁~ ▁ 2 – 3 ▁M K ) ▁in ▁the ▁interior ▁of ▁the ▁super b ubble . ▁This ▁bright ▁object ▁forms ▁the ▁background ▁for ▁the ▁" shadow " ▁of ▁a ▁fil ament ▁of ▁gas ▁and ▁dust . ▁The ▁fil ament ▁is ▁shown ▁by ▁the ▁over la id ▁cont ours , ▁which ▁represent ▁ 1 0 0 ▁mic rom et re ▁emission ▁from ▁dust ▁at ▁a ▁temperature ▁of ▁about ▁ 3 0 ▁K ▁as ▁measured ▁by ▁IR AS .