THE LIFE CYCLE OF STARS

Chapter 15 – 2Part 1

TYPES OF STARS• A star can be classified as one type

of star early in its life, and as a different type of star as it gets older.

• A star is classified differently as its properties change.

The Life Cycle of Sun-like Stars

•Like all natural cycles, the stages in a star’s life progress from birth to death.

Nebula or Protostars• A star begins life as a

ball of gas and dust.• Gravity pulls the

materials into a sphere.• As the sphere gets

denser, the temperature rises to 10,000,000* C.

• Nuclear fusion occurs as hydrogen combines into helium.

Main-Sequence Stars• After a sun-like star forms, it enters

the main-sequence.• This is the second and longest stage of

its life.• Energy is generated in the core and

causes the star to shine.• The size of the star changes very little

as long as its supply of hydrogen nuclei fuse into helium nuclei.

Nuclear Fusion

Giants and Supergiants• When a main

sequence star uses all its hydrogen in its core, helium begins to fuse.

• The center then begins to shrink, and the atmosphere grows very large and cools. ANTARES

White Dwarfs• A white dwarf is a

small, hot, and dim star that is the leftover center of a red giant.

• It slowly cools and becomes smaller, but can shine for a billion years.

SIRIUS

Let’s Review the Life Cycle of a Star

1. Nebula or Protostars

2. Main-Sequence Stars

3. Giants and Supergiants

4. White Dwarfs

LET’S TRY IT!

•ACTIVITY: THE LIFE CYCLE OF STARS