Transcript Stages 12 to 14

Stages 12 – 14
Stage 12 – Low Mass Stars
The carbon rich core continues to contract and heat up. Carbon fusion
requires a temperature of 500 to 600 million K.
The core will contract until electron degeneracy pressure once again takes
over, and contraction ends
If the star is similar to the sun, the mass is too small, the ignition temperature
is never reached.
Under the conditions under which electron degeneracy stops the contraction,
the density of the carbon rich core is about 1010 Kg/m3 !
Stage 12 – Low Mass Stars
The shells are still burning both hydrogen and
helium at a high rate.
Burning rates increase (the fusion is said to be
unstable), with explosive consequences.
Rapid releases in energy cause the shells to
expand because of intense radiation pressure.
The explosive release of energy and the
expansion causes the shells to cool, and they
will contract
Resulting increase in pressure will once again
trigger violent fusion, and the shells will expand
again.
This process will repeat itself, causing variations
in the radius of the red giant.
Stage 12 – Low Mass Stars
The inner core continues to contract an heat up, moving to the left on the HR Diagram.
The intense radiation pressure from the core pushes the shell away from the
central core.
The central core will collapse until it is supported once again by electron
degeneracy pressure.
Stage 12 – Very Low Mass Stars
M < ¼ M‫סּ‬
Extremely low mass stars will never generate enough temperature to fuse
helium. Their cores will remain helium, eventually producing a helium white
dwarf.
Stage 12 – High Mass Stars
M ≈< 8 M‫סּ‬
High mass stars can reach high enough temperatures to fuse Oxygen and
helium into Neon (see nuclear reactions overheads). These high mass stars
will eventually form the rare neon-oxygen white dwarf.
Stage 12 – Planetary Nebula
The expanding shells glow from energy
input to the gas form the central core
remnant
Hubble Reveals Details of a
Newly Born Planetary Nebula
Astronomers have caught a
peek at a rare moment in the
final stages of a star's life: a
ballooning shroud of gas cast
off by a dying star flicking on its
stellar light bulb. The Hubble
telescope has captured the
unveiling of the Stingray nebula
(Hen-1357), the youngest
known planetary nebula.
Twenty years ago, the
nebulous gas entombing the
dying star wasn't hot enough to
glow. The Stingray nebula
(Hen-1357) is so named
because its shape resembles a
stingray fish. Images of a
planetary nebula in its
formative years can yield new
insights into the last gasps of
ordinary stars like our Sun
Stage 13 – White Dwarf Stage
Eventually, the shells will drift into space, leaving the remaining hot, glowing
core to live out the rest of its life.
White Dwarf – the hot, thermally glowing remains of a star near the end of
its life cycle.
The density of the white dwarf is incredible.
If a 200 lb (as measured on the earth) person could
stand on the surface of a while dwarf, they would
weigh approximately 100,000,000 lb (ie, one hundred
million lb) !
Stage 13 – White Dwarf Stage
Isolated white dwarfs are hard to observe, and most are still in the
planetary nebula phase.
However, if they are part of a binary system, the expanding shells can
be sucked into the companion star, leaving an isolate white dwarf in
orbit around the companion star. If the white dwarf is bright enough,
these can be observed.
Stage 14 – Black Dwarf Stage
The white dwarf will continue to cool, burning itself out and becoming
a lump of space debris called a black dwarf.
The black dwarf state has not been observed