- when the supernova explodes it expels heavy elements into space, and
produces new elements (heavier than iron) in the ejecta. This is the only known
process that makes
all are: small, dense, no fusion
- masses: from <1MSun to >10MSun
- radii: ~constant => gravity-pressure balance
- pressure support needed depends on mass
- white dwarf (WD) -> neutron star (NS) -> black hole =>
sequence of mass, pressure support limits, density, radius
the exposed core of a star that has died and shed its outer layers in a
planetary nebula. It is quite hot when it first forms, because it was the
inside of a star, but it slowly cools with time.
no internal energy source -> white dwarfs cool. > black dwarf
o Its size will never change, because its electron degeneracy
pressure will forever keep it stable against the crush of gravity.
if they were gaseous they would contract as the gas pressure would
but, white dwarfs are supported by electron degeneracy pressure
Pe not dependent on temperature; depends only on density and number
o this has an interesting and important effect on the stars structure:
the more massive the star is, the smaller it is.
o masses like those of stars
o sizes (radii) like that of Earth
o can shine quite brightly in high-energy light such as ultraviolet
and X rays
o starlike mass and a small size makes gravity very strong near its
leads to an upper mass limit for white dwarfs: must be less than 1.4 Solar
Masses. What happens to more massive dead stars?
o electron speeds are higher in more massive white dwarfs
o electron speeds would reach the speed of light in a white dwarf
with a mass of about 1.4 times the mass of the Sun (1.4MSun).
the pressure that opposes gravity must come from some other source.
The source is degeneracy pressure—the same type of pressure that
supports the ―failed stars‖ that we call brown dwarfs and that arises
when subatomic particles are packed as closely as the laws of quantum
o electron degeneracy pressure: closely packed electrons