( ( ( The remains ) ( of ( the ( central star ) ) ) ) ( ( collapses ( to ( become ( a ( white ( dwarf star ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NNS remains)) (PP (IN of) (NP (DT the) (JJ central) (NN star)))) (VP (VBZ collapses) (S (VP (TO to) (VP (VB become) (NP (DT a) (JJ white) (NN dwarf) (NN star)))))) (. .)))
The remains of the central star collapses to become a white dwarf star.
(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))) (. .)))