( ( Massive stars ) ( ( ( ( die ( in ( spectacular ( supernova explosions ) ) ) ) , ) ( leaving ( behind ( ( ( ultradense ( neutron stars ) ) , ) ( which ( ( pack ( ( the mass ) ( of ( the sun ) ) ) ) ( ( into ( a ball ) ) ( ( just ( 12 miles ) ) across ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Massive) (NNS stars)) (VP (VBP die) (PP (IN in) (NP (JJ spectacular) (NN supernova) (NNS explosions))) (, ,) (S (VP (VBG leaving) (PP (IN behind) (NP (NP (JJ ultradense) (NN neutron) (NNS stars)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VB pack) (NP (NP (DT the) (NN mass)) (PP (IN of) (NP (DT the) (NN sun)))) (PP (IN into) (NP (DT a) (NN ball)) (ADVP (NP (RB just) (CD 12) (NNS miles)) (IN across))))))))))) (. .)))
Massive stars die in spectacular supernova explosions, leaving behind ultradense neutron stars, which pack the mass of the sun into a ball just 12 miles across.
(ROOT (S (NP (NN Neutron) (NNS stars)) (VP (VBP are) (NP (NP (DT the) (NNS corpses)) (PP (IN of) (NP (ADJP (VBN left) (RP over)) (NN supernova) (NNS explosions))))) (. .)))