Equations of State for White Dwarfs
This thesis is about deriving a few equations of state for white
dwarfs below the regime of neutron drip. White dwarfs - also called
degenerate dwarfs, composed mostly of electron-degenerate matter -
are luminous and the color of the light they are emitting is white,
hence their name. Because of the relatively enormous density, the
gravitational potential of a white dwarf causes a collapse.
White dwarfs are classified as compact objects, meaning that their
life begins when a star dies, and are therefore considered as
one possibility of a final stage of stellar evolution since they
are considered static over the lifetime of the Universe. Star death is
a point where the most of its nuclear fuel has been consumed. After
the birth, white dwarfs are slowly cooling, radiating away their
residual thermal energy.
White dwarfs resist the gravitational collapse with electron
degeneracy pressure. The temperature of white dwarfs is much
higher than that of normal stars. These properties, together with
exceedingly small size, are characteristic of white dwarfs. Cooling of
white dwarfs offers information of solid state physics in a new setting
- the circumstances of an original star can not be built up
in a laboratory. Also, it would not be possible to realize the
distance, which includes many advantages in sketching timescales
and fundamental interactions by observation. More over, the
evolution and the equation of state of white dwarfs provide us with
more understanding of matter and physics describing the Universe.
In this study, the equation of state for white dwarf matter
is derived first by treating the matter as ideal Fermi gas, then
including also electrostatic forces and considering the effects of
inverse β-decay. We conclude with an overview of the equation
of gravitational potential energy arising from hydrostatic equilibrium.
The accuracy of the equation of state was concluded to depend on
which interactions and phenomenon are included in the consideration.
On the other hand, choosing the white dwarf model for
an application depends significantly on the density of the matter,
as well. The equations of state of ideal Fermi gas, with Coulomb
correction and with the inverse β-decay correction were concluded to
be accurate enough to provide a quantitatively adequate description
of the phenomenon.
...


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