Formation of stars | how are stars formed?

   Formation of star : some time we look at sky and think how are stars formed? Why are stars formed? And why are star shinning in sky? How and where are heavier elements formed?. So this post for you. Start reading this post and get all your answer.

       

 How are stars formed? 

     In dark night every where in sky,we see only stars and stars are visible. Whole sky shinning with stars. And we are happy to watch these shinning stars. But sometimes we asked self how are star formed? 
     

Stars are born in nebula. Nebula are a giant clouds of dust and gas mostly hydrogen, helium and other ionized gases. Density of particles in nebula generally from 100 to 10000 particles per cm^3(in the earth atmosphere almost particle density 2.5*10^15particle per cm^3 ). So density in nebulas is too low.  And there temperature is too low like 10 to 20 kelvin and they are too cold. 
     We know atoms have mass, so they have property to attract each other.yes,there mass is too low so there gravitational Force also too low. Normally these atoms and ionized particles balanced by gravitational force among them and also their pressure.
     

But some time clouds are more dense then normally so gravitational force attract gases atoms and clouds are denser then before. As they dense temperature in core of cloud(called protostar) start to increase. More they they dense there gravitational Force pull outside normal density cloud and involve them in process. So as cloud dense as temperature in the core inverse.  By conversation of angular momentum all clouds move in spiral. This process is too slow so it's take long long time to birth The Star. 
     Temperature increased enough to start nuclear fusion reaction. Actually dutirium add up and create helium atoms. But temperature in core is very high so normal hydrogen atoms add and create helium atoms.  This process is exothermic. The star now begins to shine brightly and the radiation from star prevents further material accerting onto the star and it may disperse the remaining material in the disk that still surrounds the star. 
     When in star start nuclear fusion reaction then we say that the star is born. 
     In stars temperature is very high to create heavier elements by nuclear fusion reaction like oxygen,nitrogen and more. And upside of iron all elements create in supernova.