The Life Cycle of a Star

1
The Life Cycle of a Star
2
The nebula

• A large cloud of dust and gas
• In dense parts, gravity pulls the dust and gas
  together. Because of low temperatures gravity can
  easily overcome thermal pressure.

3
A protostar forms

• When the contracting cloud of dust and gas
  becomes dense enough and massive enough a
  protostar forms.
• Nuclear fusion has not yet started.
• The ongoing collapse increases the density making
  it difficult for radiation to escape causing an
  increase in temperature.

4
A star is born

• At 10 million K the core is hot enough for
  hydrogen fusion to start.
• Fusion stops the gravitational collapse.
• The star reaches gravitational equilibrium.

5
The fuel runs out

• When the core hydrogen is finally depleted,
  nuclear fusion stops.
• The core pressure can no longer resist the crush
  of gravity and the core begins to shrink rapidly.
• However, the outer layers expand outward.
• Hydrogen in the outer parts of the core are still
  producing fusion energy causing the expansion of
  these outer layers.

6
The death of the star

• The outer layers of the star expand and the core
  shrinks.
• The star ejects its outer layers into space.
• The core is still very hot.
• A planetary nebula may form.

7
The remains

• After a star runs out of fuel it either becomes a
  white dwarf, neutron star or blackhole.

8

• http//collab.digitaluniverse.net/wiki/Eagle_Nebul
  a
• http//library.thinkquest.org/C0126626/fate/redgia
  nt.gif
• http//domeofthesky.com/domenews/1192320000
• http//chandra.harvard.edu/photo/2002/0052/0052_xr
  ay_widefield.jpg