( ( ( ( Think ( of ( draining ( your bathtub ) ) ) ) : ) ( ( Accretion disks ) ( ( ( ( are ( ( the ( celestial equivalent ) ) ( of ( this phenomenon ) ) ) ) , ) and ) ( can ( be ( ( found ( around ( ( ( ( ( ( ( ( ( black holes ) , ) ( neutron stars ) ) , ) ( white dwarfs ) ) , ) or ) around ) ( ordinary stars ) ) ) ) ( -LRB- ( ( planets ( are ( believed ( to ( form ( from ( ( an ( accretion disk ) ) ( around ( a protostar ) ) ) ) ) ) ) ) ) -RRB- ) ) ) ) ) ) ) ) . )
(ROOT (S (S (VP (VB Think) (PP (IN of) (S (VP (VBG draining) (NP (PRP$ your) (NN bathtub))))))) (: :) (S (NP (NNP Accretion) (NNS disks)) (VP (VP (VBP are) (NP (NP (DT the) (JJ celestial) (NN equivalent)) (PP (IN of) (NP (DT this) (NN phenomenon))))) (, ,) (CC and) (VP (MD can) (VP (VB be) (VP (VBN found) (PP (IN around) (NP (NP (JJ black) (NNS holes)) (, ,) (NP (NN neutron) (NNS stars)) (, ,) (NP (JJ white) (NNS dwarfs)) (, ,) (CC or) (ADVP (RB around)) (NP (JJ ordinary) (NNS stars)))) (PRN (-LRB- -LRB-) (S (NP (NNS planets)) (VP (VBP are) (VP (VBN believed) (S (VP (TO to) (VP (VB form) (PP (IN from) (NP (NP (DT an) (NN accretion) (NN disk)) (PP (IN around) (NP (DT a) (NN protostar))))))))))) (-RRB- -RRB-))))))) (. .)))
Think of draining your bathtub:  Accretion disks are the celestial equivalent of this phenomenon, and can be found around black holes, neutron stars , white dwarfs, or around ordinary stars (planets are believed to form from an accretion disk around a protostar).
(ROOT (S (NP (NP (DT The) (JJ tidal) (NNS forces)) (PP (IN near) (NP (JJ black) (NNS holes)))) (VP (VBP are) (ADJP (RB so) (JJ great) (SBAR (S (NP (PRP they)) (VP (MD can) (ADVP (RB actually)) (VP (VB tear) (NP (NN matter)) (PP (IN from) (NP (DT a) (NN companion) (NN star))))))))) (. .)))