star’s mass determines the fate of a star
LOW/ AVERAGE MASS STAR :
stars form in huge clouds of gas(mainly hydrogen ,helium) and dust called nebulae. these areas of space containing nebulae are known as ‘stellar nurseries’ or ‘star forming regions’. when the gas particles run into each other they generate heat energy which results in the formation of warm clump of molecules referred to as protostar. gravity causes gas clouds to contract until Nuclear fusion begins
Nuclear fusion : Nuclear fusion is the process of forcing together two light atomic nuclei and creating a heavier one, in the process taking a tiny amount of matter and turning it into massive amounts of energy.
The key to understanding how fusion generates energy is Albert Einstein’s infamous equation explaining how energy equals mass times the speed of light squared (E=mc²). This tells us that matter and energy are interchangeable, while the term c² tells us that a little mass creates a lot of energy.
this fusion powers a star and establish equilibrium generating a yellow or red main sequence star. this star grows with all the energy released from the collision 💥 happening inside.
fusion in the core continues as long as it has hydrogen to fuel it. such a star will continue in this manner for billions of years , slowly fusing all of the hydrogen in its core into helium and maintaining a relatively steady size , temperature and luminosity . The outer layers are pushed away from the core to produce a red giant.
once all the hydrogen is gone the core becomes smaller and hotter and at this stage the star enters helium flash i.e. fusing heavier helium nuclei into larger nuclei — carbon and oxygen by triple alpha process. the star gets smaller , hotter and bluer until much of the helium has fused . once the core is predominantly carbon and oxygen it will collapse and the star will enter to asymptotic giant branch. the outer layers are ejected pushing it away from core back into the interstellar medium and only a small earth size core will be left which will cool soon as it has no more fuel to burn. this core will contract further into a white dwarf 🌟 . the outer layers ejected are called as planetary nebula which will then become available to join more gas particles to form yet another star.
HIGH MASS STAR :
the gas clouds are much larger in size and will contain more mass , more mass means more inward force and the star is much hotter. a hotter temperature leads to faster Nuclear fusion which results into a main sequence star which is HOT , BIG , BRIGHT and BLUE.
slowly the core becomes smaller and hotter producing more energy and the star swells up becoming more giant. each layer of core going inwards is hotter and can fuse helium nuclei to form carbon , oxygen , neon , silicon, and at the center the heaviest element iron. each heavier nucleus is relegated to smaller and smaller region of the core that is hot enough to fuse it. iron nuclei are so stable that furthermore fusion will not take place and no more energy will be released resulting in outer layers bouncing off the core in one second and a huge explosion ejecting most of the heavy nuclei back into the space. This stupendous event is known as SUPERNOVA.
particles like electrons and protons don’t want to be near each other but the pressure of collapsing star is so great that they fuse into neutrons that squeeze together as tightly as in atomic nuclei , this spawned in NEUTRON STAR . The mass of a neutron star is million times the mass of the earth but compressed to an object about 25 km wide.
BLACK HOLES : when the mass of the core is even greater , greater then three solar masses then the neutron degeneracy pressure is not enough to stop the immense gravity and the neutrons will be crushed together and all the mass of the core will be contained in a point with infinite density and zero volume known as the BLACK HOLE.