▁Here ▁the ▁fil ament ▁absor bs ▁soft ▁X - ray s ▁between ▁ 1 0 0 ▁and ▁ 3 0 0 ▁e V , ▁indicating ▁that ▁the ▁hot ▁gas ▁is ▁located ▁behind ▁the ▁fil ament . ▁This ▁fil ament ▁may ▁be ▁part ▁of ▁a ▁shell ▁of ▁neutral ▁gas ▁that ▁surr ounds ▁the ▁hot ▁b ubble . ▁Its ▁interior ▁is ▁energ ized ▁by ▁ult rav io let ▁( U V ) ▁light ▁and ▁stell ar ▁wind s ▁from ▁hot ▁stars ▁in ▁the ▁Or ion ▁O B 1 ▁association . ▁These ▁stars ▁energ ize ▁a ▁super b ubble ▁about ▁ 1 2 0 0 ▁l ys ▁across ▁which ▁is ▁observed ▁in ▁the ▁visual ▁( H α ) ▁and ▁X - ray ▁port ions ▁of ▁the ▁spectrum . ▁ ▁Pro posed ▁( f uture ) ▁X - ray ▁observ atory ▁sat ell ites ▁ ▁There ▁are ▁several ▁projects ▁that ▁are ▁proposed ▁for ▁X - ray ▁observ atory ▁sat ell ites . ▁See ▁main ▁article ▁link ▁above . ▁ ▁Ex pl or ational ▁X - ray ▁astronom y ▁ ▁Usually ▁observ ational ▁astronom y ▁is ▁considered ▁to ▁occur ▁on ▁Earth ' s ▁surface ▁( or ▁beneath ▁it ▁in ▁neut r ino ▁astronom y ). ▁The ▁idea ▁of ▁limit ing ▁observation ▁to ▁Earth ▁includes ▁orbit ing ▁the ▁Earth . ▁As ▁soon ▁as ▁the ▁observer ▁leaves ▁the ▁co zy ▁conf ines ▁of ▁Earth , ▁the ▁observer ▁becomes ▁a ▁deep ▁space ▁expl orer . ▁Ex cept ▁for ▁Explorer ▁ 1 ▁and ▁Explorer ▁ 3 ▁and ▁the ▁earlier ▁sat ell ites