there are three stages in theevolution of a typical sun like star. First is protester stage, main sequencestage, and third is red giant stage. Thisidea will tell us that how a star is born, ages, and dies. Life spans thatexceed billions of years for most stars.
Studying stellar evolution we can findout stars of different ages, at different points in their life cycles. Everystage of a star’s life is ruled by gravity. A stare is a ball of very hotgases, caught between the opposing forces of gravity. Protostar stage: at the first stage gravitational contractioncontinues much and more. This causes to the developing star to heat much faster than its outer envelope. Whenthe temperature reaches of 10 million K, the pressure within intense thatgroups of a several step process and fuse into single helium nuclei. Nowastronomers refer to this nuclear reaction and hydrogen nuclei are fused intohelium.
The heat causes the gases inside stars to move with increased vigor,raising the internal gas pressure. Outward force that balances the inward forceof gravity. Then reaching this balance, the stars become stable main sequencestars. Main – Sequence stage: inthis stage the stars minimal changes in size or energy output. Into helium wecan get Hydrogen and the energy released maintains the gas pressure high toprevent gravitational collapse. At the ending of their main sequence stage hot,blue stars got energy and they substantially deplete their hydrogen fuel inonly a few million years.
The red starsmay take hundreds of billions of years to burn their hydrogen. A yellow starlike the sun takes 10 billion years. An average star spends 90 percent of itslife burning hydrogen. Once hydrogencomes out of stars they die. With the least massive stars they die late whenanother type of nuclear reaction is triggered and the star becomes a red giant. Red Giant Stage: Whenhydrogen is consumed in star’s interior the red giant stage begins leaving ahelium rich core.
Star’s outer shell hydrogen fusion is still progressing, inthe core there is no fusion taking place. The core no longer has the gaspressure to support it self against the inward force of gravity without asource of energy. Now the core begins to contract. As gravitational energy isconverted into thermal energy, The collapse of a star’s interior causes itstemperature to rise rapidly . In the shell a more vigorous level of hydrogenfusion surrounding the star’s core.
From accelerated rate of hydrogen fusionexpands the star’s outer gaseous shell using the additional heat. Sun likestars become bloated red giants.