THE EVO­LU­TION OF STARS

iD magazine - - Space -

»The life of a sun of­ten lasts for bil­lions of years— and yet each has a very spe­cific ex­pi­ra­tion date. This can be pre­cisely cal­cu­lated by look­ing at the amount of nu­clear en­ergy re­serves it has (mainly hy­dro­gen and he­lium). Once this fuel has been used up, an un­stop­pable process of dis­in­te­gra­tion be­gins— the star dies. But the fate of the star af­ter its death de­pends on how mas­sive it was dur­ing its life­time. A star that has a resid­ual 1.44 so­lar mass (around 3.2 oc­til­lion tons) be­comes a blind­ingly bright white dwarf. On the other hand, a dy­ing star of 1.44 to 3 so­lar masses ends in a big bang— a supernova. Af­ter that it ekes out an ex­is­tence for many mil­lions of years as a neu­tron star— an ex­tremely dense sphere with a di­am­e­ter of 12 miles. The end is dif­fer­ent for gi­ant stars with more than 3 so­lar masses. They also ex­plode, but they sub­se­quently mu­tate into black holes. Ex­perts pre­dict that our Sun’s hy­dro­gen re­serves will last about 5 to 6 bil­lion more years at most.

The cloud is mainly made of hy­dro­gen. The gas is held to­gether by its own grav­ity in space. If its grav­i­ta­tion ex­ceeds a crit­i­cal point, the cloud col­lapses and a star is formed. Such a star has a mass, for ex­am­ple, equiv­a­lent to that of our Sun. (1 so­lar

small star red gi­ant large star molec­u­lar cloud

The hy­dro­gen has been con­sumed, and the star ex­pands. Such a gi­ant is around 1,500 times as big as our Sun— and 100,000 times brighter. The dy­ing star opens its shell— from which gas and plasma spread like mist. It’s a process that gives rise to heavy ele

red su­per­giant white dwarf neu­tron star black hole supernova plan­e­tary neb­ula

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