Life Cycle of a Star- How Fusion Makes Sunlight By Caio Life Formation of a Star • All stars begin as Nebulae, giant clouds of dust and gas in space. • Once a nebula gains sufficient mass it will begin to collapse under its own gravity and spin. • This spinning and extreme gravity causes the core to heat up and becomes a Protostar. • The core’s temperature continues to rise until it reaches around 15,000,000°C and fusion is able to begin. “Pillars of Creation” from the Eagle Nebula • The fusion prevents further gravitational collapse as the fusion causes increased thermal pressure and a star is created. Fusion • When two atoms collide with a large enough force they will fuse to form a new atom with a smaller mass. • This mass can be released as radiation, positrons, photons or neutrinos. • The positrons annihilate when they come into contact with an electron as they have equal and opposite charge and release two photons • The radiation, photons and neutrinos are released by the sun and may travel to earth • The amount of energy release by this fusion can be calculated using the famous equation E=mc2 Main Sequence • Initially, the star remains in stable equilibrium • Low mass such as our sun stars spend billions of years fusing hydrogen to helium • As the hydrogen is used up it shrinks and gains temperature • Eventually all the hydrogen is fused into helium and fusion is no longer able to occur Red Giant • The decrease in thermal pressure causes the core to collapse • The radiation pressure is so great that the outermost layer of the star expand • Eventually the core becomes hotter and denser and reaches a temperature of 100 million K and helium nuclei begin to fuse into carbon. Death of a Star • The outer layer of the Red Giant continues to expand until gravity can no longer contain it • This forms what is know as a Planetary Nebula • The carbon core will eventually cool and become a white dwarf, the dense dim remnant of a once bright star • The cooling core is called a white dwarf, and eventually can no longer be seen and is then called a black dwarf. Any Questions?
