2. THE LIFE CYCLE OF A STAR Objective: I will compare and contrast the life cycle of stars based on their mass.

3. What is a Star? A star is ball of gas undergoing nuclear fusion Stars give off large amounts of energy in the form of light and heat (electromagnetic radiation)

4. Formation of a Star Stars are formed in a nebula, a very large cloud of gas and dust in space.

5. Protostars Gravity causes dense areas of gas take on a definite shape and are called protostars.

6. A Star is Born! Once the core of a protostar reaches 10,000,000 K, nuclear fusion begins and the protostar becomes a star. The bright spot is a new star igniting

7. Nuclear Fusion Nuclear Fusion is the process by which two nuclei combine to form a heavier element. New stars initially will fuse hydrogen nuclei together to form helium.

8. Life Cycle of a Star

9. Main Sequence Stars Once nuclear fusion occurs, a star enters the main sequence Stars live most of their life in the main sequence In smaller stars, it takes about 10 billion years to consume all the hydrogen in the main sequence

10. A Delicate Balancing Act Two forces acting on the star: inward force of gravity and outward force of energy caused by fusion Once fusion of hydrogen stops, the star collapses inward due to gravity

11. Red Giant Collapsing outer layers cause core to heat up. Fusion of helium into carbon begins. Forces regain balance. Outer shell expands greatly Red Giants last for about 100 million years.

12. Unbalanced Forces (again) When the Red Giant has fused all of the helium into carbon, the forces acting on the star are again unbalanced. The massive outer layers of the star again rush into the core and rebound, generating staggering amounts of energy. What happens next depends on how much mass the star has.

13. Mass Matters Red Giant Mass < 3 x sun White Dwarf Black Dwarf Mass > 3x sun Red Supergiant Supernova Neutron StarBlack Hole

14. White Dwarf  Black Dwarf Star’s outer layers drift away and become a planetary nebula. A white dwarf is left over and the core cools over time into a black dwarf Planetary nebula around a white dwarf star.

15. Red Supergiants Massive stars with go from Red Giants to Red Supergiants Fusion of heavier elements such as carbon into iron begins

16. Supernova Massive explosion of a red supergiant. All elements heavier than iron are produced in supernovas Gas ejected from a supernova explosion

17. Neutron Star or Black Hole Neutron star- left over core from a supernova Black hole- core so dense and massive that it will generate so much gravity that not even light can escape it.