In a kind of star assembly line, interstellar molecular clouds collapse, producing new stars, which then gradually push back the remaining gas and dust.
类似于一条恒星生产线，星际间分子云瓦解产生新恒星，然后新的恒星逐渐将剩下的气体和尘埃推走。
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The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star's remaining core.