( Stars ( ( ( are essentially ) ( ( ( huge balls ) ( of ( ( extremely hot ) gas ) ) ) ( that ( ( generate ( energy ( in ( their centers ) ) ) ) ( through ( ( a process ) ( called ( nuclear fusion ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Stars)) (VP (VBP are) (ADVP (RB essentially)) (NP (NP (JJ huge) (NNS balls)) (PP (IN of) (NP (ADJP (RB extremely) (JJ hot)) (NN gas))) (SBAR (WHNP (WDT that)) (S (VP (VBP generate) (NP (NP (NN energy)) (PP (IN in) (NP (PRP$ their) (NNS centers)))) (PP (IN through) (NP (NP (DT a) (NN process)) (VP (VBN called) (NP (JJ nuclear) (NN fusion)))))))))) (. .)))
Stars are essentially huge balls of extremely hot gas that generate energy in their centers through a process called nuclear fusion.
(ROOT (S (NP (NP (JJ Nuclear) (NN fusion)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ results) (PP (RB because) (IN of) (NP (NP (JJ great) (NN pressure)) (PP (IN at) (NP (NP (DT the) (NN center)) (PP (IN of) (NP (DT a) (NN star)))))))))) (, ,)) (VP (VBZ causes) (S (NP (NNS stars)) (VP (TO to) (VP (VB shine))))) (. .)))