Cas a is the 300 - year - old remnant created by the supernova explosion of a massive star 仙后座a是有着300年历史的遗迹，成因是大质量恒星的超新星爆发。
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This spectacular image of the supernova remnant cassiopeia a is the most detailed image ever made of the remains of an exploded star 这张壮观的仙后座a照片是迄今对爆发恒星的残骸拍摄过的最精细的照片。
