Life Cycle of a Star

1. Life Cycle of a Star

2. Birth of a Star • Starts in a nebula • A nebula is a giant cloud of gas and dust

4. Birth of a Star • Gravity in the nebula gradually pulls the hydrogen together which causes it to spin. • This spinning and the atoms bumping into each other creates heat. • Once the temperature of this spinning mass of gas reaches 15 million degrees fusion begins and a star is born.

5. Fusion • Fusion is when two nuclei combine to form one heavier nucleus. • Typically the resultant nucleus has less mass than the initial nucleuses together. It’s this loss in mass that causes the extreme amounts of energy and heat created. • Inside a star gravity creates a pressure so great that the electrons are stripped creating a plasma. This plasma inside the core is where the fusion takes place.

6. Main Sequence Stars • The fusion creates an outward pressure of energy that counteracts the inward pull of gravity. • Once this energy reaches they outer layers of the star it is emitted as electromagnetic radiation.

8. Here we go again • Once all the hydrogen is depleted gravity again takes control creating more and more pressure on the now helium core. • This pressure creates heat just as it did before causing fusion. • Now we have a Red Giant

9. Red Giants Continually increase in size Higher density core, output energy from fusion is greater

11. Different Paths

12. Sun sized stars • Helium core continues to fuse until it reaches a solid carbon state. • When this happens it sheds it outer envelope into what is called a planetary nebula.

13. The White Dwarf • It is one millionth the size of the original star. • No nuclear process is occurring so what is keeping it from collapsing on itself.

14. High density matter causes low amounts of room for electrons in the lower energy shells, forcing them into the higher ones giving off energy.

16. Black Dwarfs • After the white dwarf has expelled all of its energy in the process of cooling down it no longer gives off light and is considered a black dwarf.

17. Medium sized stars • Their nuclear fusion does not stop after the reaches its carbon state. • Continues until reaches an iron core, and is extremely dense. • The incoming matter creates pressure and heat eventually causing the repulsive force between the nuclei over powers the force of gravity and a supernova occurs.

18. Neutron Star • They are small and massive objects • Some can be considered pulsars • 1.4 times mass of sun and only ten mile diameter

19. Black Holes • Gravitational pull is so strong light cannot escape. • Star collapses into its event horizon

20. Questions • What is the main factor in determining the cycle of the star? • What two forces are acting to counterbalance one another inside a star? • What occurs during fusion? • Where does a star begin its life? • What are the possible states that a star winds up in?

21. Questions • What causes solar flares? • Why can you see the “shells” of a planetary nebula?