( ( When ( neutron ( stars collapse ) ) ) ( , ( ( their atoms ) ( ( ( break apart ) ( into ( ( ( their ( subatomic particles ) ) , ) quarks ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NN neutron)) (VP (VBZ stars) (NP (NN collapse))))) (, ,) (NP (PRP$ their) (NNS atoms)) (VP (VBP break) (ADVP (RB apart)) (PP (IN into) (NP (NP (PRP$ their) (JJ subatomic) (NNS particles)) (, ,) (NP (NNS quarks))))) (. .)))
When neutron stars collapse, their atoms break apart into their subatomic particles, quarks.
(ROOT (S (NP (NP (DT The) (NN number)) (PP (IN of) (NP (NNS neutrons)))) (VP (MD can) (VP (VB vary) (PP (IN between) (NP (NP (NNS atoms)) (PP (IN of) (NP (DT the) (JJ same) (NN element))))))) (. .)))