5/11/2010Earth Science 25.2A : Stellar EvolutionThe Birth and Evolution of Stars
5/11/2010Earth Science 25.2 : Stellar EvolutionDetermining how stars are born, age and die can be difficult because the life of a star can span billions of years.However, by studying stars of different ages astronomers have been able to piece together the life and evolution of a star.
5/11/2010Earth Science 25.2 : Stellar EvolutionThe Birth of a Star:The birthplaces of stars are dark, cool interstellar clouds.These nebulae are made up of dust and gases. In the Milky Way, nebulae consist of 92% hydrogen, 7% helium, and less than 1 % of the remaining heavier elements.For some reason not fully understood by scientists, some nebulae become dense enough that they begin to contract, growing smaller yet denser as they shrink.
5/11/2010Earth Science 25.2 : Stellar EvolutionA shock wave from another nearby star may trigger this contraction.Once this process begins to occur, gravity squeezes particles in the nebulae pulling each and every particle toward the center.As the nebulae shrinks and grows denser in it’s center, this gravitational energy increases and is converted into heat energy.
5/11/2010Earth Science 25.2 : Stellar EvolutionProtostar Stage:The initial contraction of gases spans a million years time.As time passes, the temperature of this gas body slowly rises enough to radiate energy from it’s surface in the form of long-wavelength red light.This large red object is called a protostar; a developing star that is not yet hot enough to attain nuclear fusion.
5/11/2010Earth Science 25.2 : Stellar EvolutionDuring the protostar stage, gravitational contraction continues: slowly at first than more rapidly.This collapse causes the core of the protostar to heat much more intensely than the outer layer.When the core of a protostar has reached about 10 million degrees K, pressure within it is so great that the nuclear fusion of hydrogen begins, and a star is born.
5/11/2010Earth Science 25.2 : Stellar EvolutionHeat from hydrogen fusion causes the gases to increase their motion.