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Stellar evolutionnStellar evolution is a Processnduring which a Star Changesnover time.nStars can have life from fewnmillion to trillion years.nStar is formed from cloud ofngas and dust called Nebula.nA proto star is formed when regionnof nebulae collapse under gravitynAs contents density increase, hencenTemperature and KE of Particles increase.nOver time, the velocity of Particlesnincreases hence Temperature andnKE increase to increase.nAfter millions of years Proto starnreaches State of equilibriumnKnown as Main Sequence StarnAs Temperature increase Pressurenalso increase, in Stable Starninternal gravity is balanced bynexternal pressure.nThis condition is described bynhydrostatic equationnAP/AR = GMB/R^2nThis equation means that anStar neither contracts nor expandsnindefinitely.nIn the EquationnP is pressure inside StarnOP change in Pressure with radiusnP is pressure from CenternG is gravitational Constant.nM is mass inside radius rnPr is density at rnNegative sign meansnincrease outward gravitynPull is insteadnImbalance between Two forcesn-> Gravitational force > internal pressurenthen Star Contractsn-> If internal pressure > gravitational forcenthen Star expandnRole of Nuclear fusionnContinuous fusion powers the Starnon well an increases temperaturenand causes the Star to expand intonRed giant