When the density of hydrogen atoms went up to above 60000 per cubic centimeter in space because normally it is 1 per cubic centimeter, the matter outside the cubic centimeter will fall to the centre of the it which makes the homogeneous gas become a group of hydrogen atoms which has extremely high density at one single point and surround by rarefies but thick”atmosphere” on the outside. This will results more and more hydrogen atoms been pulled into the “singularity” with faster and faster speed. The process could last for about one hundred thousand years and until it’s singularity is getting denser and denser, bigger and bigger, hotter and hotter, after the hydrogen atoms all move fiercely, after the hydrogen atoms lost all their electrons, after the singularity achieved ten million degrees, an epic that last for ten billion years begins.
An extremely bright light appears, the whole universe seems to changed from black to white, with the γ ray, β ray, α ray, with different sorts of electronic magnetic wave and gravitational wave, a young star appears. This star unscrupulously shows the universe it’s unimaginable power by nuclear fusion reaction in the centre of itself.
During the next few billions of years, this star keeps fighting with its own gravitational pressure by using the radiation repulsive force which was produced by the huge amount of energy that was lost during the nuclear fusion. At this stage, this star is well balanced with the radiation repulsive force and the gravitational pressure so it is calm and comfortable because it has plenty of hydrogen as reactant to react.
Everything has a beginning and an ending. Including the universe, stars also die. As soon as the hydrogen runs out, the calm period ends. The balance between the radiation repulsive force and the gravitational pressure will soon be broken. The star will soon dim down and collapse under its own gravity. Aye, but not yet to die! Because of the collapse, the core got pressurized therefore the temperature increase in a instant, it lit up the helium for its nuclear fusion power and expand quickly again just as it was born. This is what we called- the helium flash. Under the unimaginable gravitational pressurization and ten million degrees, helium atoms start grabbing other two helium atoms to form carbon atoms. Then the carbon atom will grab another helium atom to form oxygen. These reactions are not as gentle as hydrogen fusion reaction, they shine and react in a sudden which is what we called- the helium flash.This will make the helium in the core burnt out first so the it has to burn the helium with is outside the core. This will results to the big expansion of the star that makes the star expands about one billion times bigger and because it expands, the temperature drops fast that make it changes from bright yellow to red. This is what we called- the Red giant star. But because of the size expanded, it still looks extremely bright with low temperature so the brightest star in the night sky are mostly red giant star.
After millions of year, after the reactive elements run out, after the iron appears, the efficiency of nuclear fusion drops fast and finally, the end of the epic appears. There are four possible endings for a star and they are a White drawf, a Supernova, a Neutron star or to become a Blackhole.
