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 H-R 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 Mּס

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 Mּס

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