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ASTRONOMY

ASTRONOMY. Chapter 28 The Aging and Death of Stars Like the Sun. Low-mass Stars. Low-mass stars are stars with masses less than about 8 M˳. This includes the vast majority of stars. End of Main Sequence Life.

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ASTRONOMY

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  1. ASTRONOMY Chapter 28 The Aging and Death of Stars Like the Sun

  2. Low-mass Stars • Low-mass stars are stars with masses less than about 8 M˳. • This includes the vast majority of stars.

  3. End of Main Sequence Life • During its 10 billion years on the main sequence, our sun will fuse all of the hydrogen in it’s core. • During this time, the star is in hydrostatic equilibrium. • The core now contains only helium. • Hydrogen is still fusing in a shell surrounding the core.

  4. End of Main Sequence Life • No Fusion inside the core means: • Hydrostatic equilibrium is lost • Core contracts gravitationally • Core gets hotter • Shell of fusing hydrogen gets hotter causing the rate of fusion to increase • Outer layers of the star are heated and expand outward • Surface temperature decreases due to increased surface area

  5. Red Giants http://25.media.tumblr.com/tumblr_l5pd17Hys51qa0fruo1_400.jpg

  6. Red Giants • Our sun will swell to nearly the size of the Earth’s orbit. • The core continues to contract and heat up. • When the core reaches 108 K which starts the triple alpha reaction. • For stars like our sun this happens rapidly and is called a helium flash. • He fuses in the core forming carbon and oxygen.

  7. Planetary Nebulae • When the C core forms, it contracts and heats up just like the He core • H and He fusing shells form and are unstable • The star begins to pulsate, losing some mass with each pulsation • These gas envelopes move out and become transparent • A planetary nebula is formed.

  8. Planetary Nebulae

  9. Planetary Nebulae

  10. Planetary Nebulae

  11. Planetary Nebulae

  12. White Dwarfs • Red Giant stars are not massive enough to fuse C • Stars with Masses up to 8 M˳ lose much of their mass and are now at or below 1.4 M˳ • They shrink and become stable and very hot and are called white dwarfs. • They are very faint, being below and to the left of the main sequence.

  13. Black Dwarfs • The white dwarf radiates energy for billions of years • There is no source of new energy • It cools and eventually becomes a black dwarf. • We do not think that any white dwarf has reached this stage yet.

  14. Novae • Some white dwarfs in binary systems will collect gas from the other star. • When enough has accumulated, the white dwarf will again begin fusing the H • It becomes much brighter in a matter of days, then gradually dimming • These newly visible stars are called novae

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