Download Energy Production in Stars

Energy Production in Stars
 Stars are at enormous distances, yet we can see thousands => extremely
luminous
 What is the source of their enormous energy?
o Thermonuclear reactions (fusion) that convert mass to energy
 In the special theory of relativity Einstein demonstrated that
the total mass-energy was conserved => e = mc2
 Speed of light squared is a very large number => small amount
of mass corresponds to a huge amount of energy
 The conversion of mass to energy accounts for the enormous
energy output of the stars
 What physical mechanisms can cause this?
 Nuclear fission - splitting of an atom's nucleus
 Nuclear fusion - sticking two nuclei together
 Nuclear fusion is favored because:
o The most stable nuclei in the universe is Fe
o Demonstrated by the Curve of Binding Energy
o
o Stars are made of light elements (mostly H and He)
and favor a reaction that makes them closer to the
structure of Fe
 To combine, nuclei must overcome the coulomb barrier => provides a
strong resistance to nuclear fusion in stars
 The greater the density and temperature of a star, the greater probability
(and the actual amount) of fusion
Interior of Stars
 Information on a star's interior gathered from observations of the Sun
 Core
o Dense (12 times that of solid lead) => 1/3 the total mass of the star
o Nuclear fusion takes place here
o Ends ¼ of the distance to the surface
 Radiation Zone
o Less dense than the
core (~ density of
H2O)
o Energy from the core
is absorbed and reemitted many times
(photons move
through like a drunken
sailor) => can take
millions of years
o Ends ½ of the distance
to the surface
 Convection Zone
o Density much less (~ 1% the density of H2O)
o Gases heated at the bottom of zone, rise to the surface
(photosphere), release energy, cool, and sink back to the bottom