( ( ( ( ( ( ( When even ) ( ( the helium ) ( is gone ) ) ) ( , ( ( the core ) ( collapses ( into ( a ( white ( dwarf star ) ) ) ) ) ) ) ) , ) and ) ( ( the ( outer parts ) ) ( ( ( escape ( into space ) ) , ) ( forming ( an ( expanding shell ) ) ) ) ) ) . )
(ROOT (S (S (SBAR (WHADVP (WRB When) (RB even)) (S (NP (DT the) (NNP helium)) (VP (VBZ is) (VP (VBN gone))))) (, ,) (NP (DT the) (NN core)) (VP (VBZ collapses) (PP (IN into) (NP (DT a) (JJ white) (NN dwarf) (NN star))))) (, ,) (CC and) (S (NP (DT the) (JJ outer) (NNS parts)) (VP (VB escape) (PP (IN into) (NP (NN space))) (, ,) (S (VP (VBG forming) (NP (DT an) (VBG expanding) (NN shell)))))) (. .)))
When even the helium is gone, the core collapses into a white dwarf star, and the outer parts escape into space, forming an expanding shell.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT the) (NNP helium)) (VP (VBZ is) (VP (VBN gone))))) (, ,) (NP (DT the) (NNS stars)) (VP (VBP become) (NP (JJ white) (NNS dwarfs))) (. .)))