1. What is the Lifecycle of a Star? Chapter 30.3

2. Stars form when a nebula contracts due to gravity and heats up (see notes on formation of the solar system). Stars form when a nebula contracts due to gravity and heats up (see notes on formation of the solar system). When the pressure and temperature in the protostar is enough, fusion of hydrogen into helium begins. This is the birth of a star. When the pressure and temperature in the protostar is enough, fusion of hydrogen into helium begins. This is the birth of a star. Once fusion begins, there is an outward force that balances the inward force of gravity. The star will remain stable. (Main sequence.) Once fusion begins, there is an outward force that balances the inward force of gravity. The star will remain stable. (Main sequence.)

3. Once the fusion of H  He ends in a star, the star will begin to die. How it will end up depends on how much mass it has. Once the fusion of H  He ends in a star, the star will begin to die. How it will end up depends on how much mass it has. A star with a mass like ours will begin contracting again, due to gravity. The outer layers will expand and cool, causing the star to become a Red Giant. A star with a mass like ours will begin contracting again, due to gravity. The outer layers will expand and cool, causing the star to become a Red Giant. This outer material will eventually become interstellar matter. This outer material will eventually become interstellar matter. The inner portion will contract and become a white dwarf, undergo fusion up to C and eventually cool off, leaving a lump of carbon The inner portion will contract and become a white dwarf, undergo fusion up to C and eventually cool off, leaving a lump of carbon

4. A star more massive than the Sun will continue undergoing different phases of fusion while a white dwarf, producing the elements up to Fe (iron). A star more massive than the Sun will continue undergoing different phases of fusion while a white dwarf, producing the elements up to Fe (iron). Stars that are more than 8 times the mass of our Sun won’t end up as white dwarfs. Stars that are more than 8 times the mass of our Sun won’t end up as white dwarfs. Once it runs out of fuel to produce iron, the star collapses due to gravity, and explodes outward in a “supernova.” This supernova explosion produces all the elements from Fe to U (uranium), throwing them into space. Once it runs out of fuel to produce iron, the star collapses due to gravity, and explodes outward in a “supernova.” This supernova explosion produces all the elements from Fe to U (uranium), throwing them into space. A dense neutron star is left behind. A dense neutron star is left behind. Stars with 20 times the mass of our Sun will leave behind a black hole. Stars with 20 times the mass of our Sun will leave behind a black hole.