1. Chapter 19
Section 2 The Life Cycle of Stars
Bellringer
Supernovas represent the “death” of stars that exceed a certain mass. In a few seconds, a supernova can release more energy than it previously did in its entire existence. Look at the photographs of Supernova 1987A and the Large Magellanic Cloud taken before the explosion.
Record and illustrate your answers in your notebook.

2. Chapter 19 Objectives Describe different types of stars.
Section 2 The Life Cycle of Stars
Objectives
Describe different types of stars.
Describe the quantities that are plotted in the H-R diagram.
Explain how stars at different stages in their life cycle appear on the H-R diagram.

3. The Beginning and End of Stars
Chapter 19
Section 2 The Life Cycle of Stars
The Beginning and End of Stars
The Beginning A star enters the first stage of its life cycle as a ball of gas and dust. Gravity pulls the gas and dust together, and hydrogen changes to helium in a processes called nuclear fusion.
The End Stars usually lose material slowly, but sometimes they can lose material in a big explosion. Much of a star’s material returns to space, where it sometimes forms new stars.

4. Different Types of Stars
Chapter 19
Section 2 The Life Cycle of Stars
Different Types of Stars
Stars can be classified by their size, mass, brightness, color, temperature, spectrum, and age. A star’s classification can change as it ages.
Main-Sequence Stars After a star forms, it enters the second and longest stage of its life cycle known as the main sequence. Energy is generated in the core as hydrogen atoms fuse into helium atoms.

5. Different Types of Stars, continued
Chapter 19
Section 2 The Life Cycle of Stars
Different Types of Stars, continued
Giants and Supergiants After the main-sequence stage, a star can enter the third stage of its life cycle. A red giant, as it is know known, is a large, reddish star late in its life cycle.
In this third stage, a star can become a red giant. As the center of the star shrinks, the atmosphere of the star grows very large and cools to form a red giant or a red supergiant.

6. A Tool for Studying Stars
Chapter 19
Section 2 The Life Cycle of Stars
A Tool for Studying Stars
The H-R Diagram the Hertzprung-Russell diagram is a graph that shows the relationship between a star’s surface temperature and absolute magnitude.
Reading the H-R Diagram The diagonal pattern on the H-R diagram where most stars lie is called the main sequence. Find the diagonal pattern in the H-R Diagram on the next two slides.

7. Chapter 19
Section 2 The Life Cycle of Stars
H-R Diagram

8. Chapter 19
Section 2 The Life Cycle of Stars

9. Chapter 19 When Stars Get Old
Section 2 The Life Cycle of Stars
When Stars Get Old
Supernovas A supernova is a gigantic explosion in which a massive blue star collapses.
Neutron Stars and Pulsars A star that has collapsed under gravity to the point at which all of its particles are neutrons is called a neutron star. If a neutron star is spinning, it is called a pulsar.

10. When Stars Get Old, continued
Chapter 19
Section 2 The Life Cycle of Stars
When Stars Get Old, continued
Black Holes Sometimes the leftovers of a supernova are so massive that they collapse to form a black hole. A black hole is an object that is so massive that even light cannot escape its gravity.