Core hydrogen burning
On the main sequence, a star slowly fuses hydrogen into helium
What happens when a star consumes all of its hydrogen?
The star's internal balance begins to shift, and both its internal structure and outward appearance begin to change
-The star leaves the main sequence
What is the determining factor in the death of a star?
Low mass stars die gently, and high mass stars die catastrophically
Stage 8
-As nuclear fusion proceeds, the composition of the star's interior changes as its hydrogen fuel is depleted
-The helium content increases fastest in the core where temps are higher and burning the fastest
-As the star's core weakens and the shrinkage of
Hydrogen shell burning
As hydrogen is burning at a much faster rate, the helium isn't hot enough to burn, so the leftover hydrogen gets pushed to an outer layer of the core. The shell's energy production continues to increase as the helium core continues to shrink
Stage 9
-Star is no longer in stable equilibrium
-The helium core is unbalanced and shrinking
-The pressure from the hydrogen burning causes the star's outer layers to increase in radius (expanding and cooling)
-The transformation from main-sequence to the elderl
Stage 10
A hundred million years after the star leaves the main-sequence, helium now becomes a source of fuel
What is the triple alpha process?
First, 2 helium atoms get fused together to form an isotope of beryllium (Be-8)
It becomes fused with a helium atom to become carbon 12
The helium flash
While helium burning is occurring and the temperature is rising, the pressure never changes
-this leaves the core susceptible to this runaway condition. The chemical reactions become unstable and while pressure doesn't react, the energy grows with the pot
Stage 11
-The dying star's rich carbon core is burning at an extremely high rate
-the helium fuel doesn't last long (a few 10 million years after the helium flash)
-as helium fuses to carbon, a new carbon-rich inner core begins to form, in a phenomena similar to t
Stage 12
-The envelope continues to expand until it is about 300 times the size of mars
-The helium-burning shell undergoes several helium-shell flashes, caused by enormous pressure buildup
-Eventually all of the star's envelope will be ejected into space in less
Stage 13
-Carbon core continues to evolve
-It is not visible as the envelope recedes (over tens of thousands of years)
-Size of about Earth.
-Shining only by stored heat not nuclear reactions
-Dim because of its size
-Not all WD's are found in the center of PN's
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