Download Stellar Structure

Flow of energy
Stellar Structure
Energy transport
via convection
Sun
Energy transport
via radiation
Energy
generation via
nuclear fusion
Basically the same
structure for all stars
with approx. 1 solar
mass or less.
Temperature, density
and pressure decreasing
What would happen if the sun
suddenly stopped producing
energy in its center?
1.
2.
3.
4.
5.
It would explode.
It would rapidly collapse.
It would gradually cool off
and shrink.
It would gradually cool off
and expand.
It would maintain its current
structure.
Hydrostatic Equilibrium
Outward pressure of
hot gas in the center
balances the
inward force due to
gravity.
Hydrostatic
Equilibrium
Outward pressure force
must exactly balance the
weight of all layers above
any given point in the star.
This condition uniquely
determines the interior
structure of the star.
This is why we find stable
stars on such a narrow strip
(Main Sequence) in the
Hertzsprung-Russell diagram.
How does the sun
produce energy in its
center?
1.
2.
3.
4.
5.
Through chemical burning of
hydrogen (2 H + O → H2O).
Through thermonuclear fusion of
helium into Carbon.
Through thermonuclear fusion of
hydrogen into helium.
Through thermonuclear fission of
helium into hydrogen.
Through thermonuclear fission of
Uranium into lighter nuclei.
The CNO Cycle
In the sun, energy
production is
dominated by direct
fusion of H into He
(PP chain).
In stars slightly more
massive than the
sun, a more powerful
energy generation
mechanism than the
PP chain takes over:
The CNO Cycle.
Energy Transport Structure
Inner convective,
outer radiative
zone
Inner radiative,
outer convective
zone
CNO cycle dominant
PP chain dominant
Summary:
Stellar Structure
Convective Core,
radiative envelope;
Energy generation
through CNO Cycle
Radiative Core,
convective envelope;
Energy generation
through PP Cycle
Sun