Stellar Evolution

1
Stellar Evolution

• Chapter 30.2

2
Classifying Stars

• -H-R diagram- Used to plot surface
• temperature and absolute
• magnitude (brightness).
• -Main-sequence stars- stars that fall
• within a band running through the middle of
  diagram.
• (Fig. 1 page 781)
• Cool, red, dim stars lower right
• Hot, blue, bright stars upper left
• Cool, red, bright stars upper right
• Hot, blue, dim stars lower left

3
Star Formation

• 1. Stars begin as a nebulacloud of gas dust.
• -Gas consists mainly of Hydrogen and Helium.
• 2. Nebula forms into a Protostarnebula begins to
  flatten into a disk of matter.

4
Star Formation continued

• 3. Nuclear fusion- A star begins to form when
• H H ? He occurs in the core.
• -As gravity increases the rate of fusion
  increases.
• -As long as fusion is occurring, the star
  becomes what we call a main sequence star.
• Our Sun!

5
Star Formation continued

• 4. Main Sequencelongest stage in a stars life.
• -Energy continues to generate in the core
  (Fusion of H into He).
• -A star in this stage can stay there about 10
  billion years.
• -When fusion stops, the star will move into
  another stage no longer a main sequence star.

6
Star Formation continued

• 5. Giant and Supergiants- Almost all H atoms
  have fused into He atoms.
• -a stars shell of gases grows cooler as it
  expands begins to glow a reddish color.
• -they look bright because of their size.

7
Star Formation continuedthe Final Stages!

• 6. Energy is exhausted!
• -Planetary Nebulas form a cloud of gas that
  forms around a sun-like star that is dying.
• -White dwarfs As the planetary nebula
  disperses, gravity causes the remaining matter to
  collapse inwardwhat is left is hot denseit is
  called a white dwarf.
• -When a white dwarf no longer gives off light,
  it forms a black dwarf.

8
Star Formation continuedthe Final Stages!

• 7. Nova - from white dwarfs large explosions
  which releases energy stellar material into
  space.
• Supernova - from white dwarfs as well (after
  super giant stage) a star that has such a
  tremendous explosion that it blows itself apart.
• -After a supernova the core may contract into a
  very small but dense ball of neutrons called a
  neutron star.
• -A neutron star may turn into a Pulsars - a
  very fast spinning star that emits pulses of
  radio optical energy.
• -A supernova may lead to a Black Hole a star so
  massive dense that even light cannot escape its
  gravity.