Star Life Cycle
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Star Life Cycle. Fill in the chart when you see a yellow star. Take notes on the stars and events as well. . STARS. All stars begin the same way, but the last stages of life depend on it’s mass. The birth place of stars are Nebulas, often referred to as “stellar nurseries”.
Star Life Cycle
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Presentation Transcript
Star Life Cycle Fill in the chart when you see a yellow star. Take notes on the stars and events as well.
STARS • All stars begin the same way, but the last stages of life depend on it’s mass. • The birth place of stars are Nebulas, often referred to as “stellar nurseries”. • Nebulas are clouds of dust and gas.
3 TYPES OF NEBULAE • Emission: emit radiation, usually appear red • Reflection: reflect light of nearby star, usually appear blue. • Dark: block light, appear black.
Nebula: Accretion disc • Gravitational attraction causes gas and dust to condense, spin and heat up which forms a proto-star.
Proto-stars • There are no nuclear reactions inside the proto-star, it is not a star yet!
Brown Dwarfs • If there is not enough mass to create a protostar, a Brown Dwarf forms. • Some astronomers consider Jupiter a Brown Dwarf…
A star is born… • Eventually the gas shrinks enough that its temperature and density become high enough, that a nuclear fusion reaction starts in its core! -- It becomes a giant Hydrogen Bomb!
A star is born… • At 10 Million K, Hydrogen begins nuclear fusion to form helium and the star begins to shine. • It will now be visible on an H-R Diagram.
Main Sequence Star • The star shines as nuclear reactions inside produce light and heat.
How it works: • How long and how hot the star burns is determined by the star’s mass but… • Eventually, stars begin to run out of their fuel hydrogen. • The problem is that pressure begins to decrease but gravity stays the same causing contraction, which raises pressure which increases temperature.
How it works… • Hydrogen shell begins to burn rapidly (red layer in the diagram) and this causes the non-burning helium ‘ash’ (yellow layer) to expand. • The core shrinks and heats up, the outer layers expand and cool. This is a red giant.
Red Giant • Star of less mass expands and glows red as it cools.
Planetary Nebula • In the core, helium begins fusing to make carbon. Temperatures are not high enough to make heavier elements. • Helium flash: burning of helium becomes explosive and the outer layers of red giant are ejected in an envelope called a planetary nebula.
Planetary Nebula • Outer layers of gas puff off. • Hot core will be exposed as white dwarf.
White dwarf • As the envelope recedes, the core becomes visible.
White Dwarf • Small, dim and hot. • No nuclear reactions • Dying star that is slowly cooling off
Nova • A nova is a white dwarf star that suddenly increases enormously in brightness, then slowly fades back to its original luminosity. • Novea are the result of explosions on the surface of the star caused by matter falling onto their surfaces from the atmosphere of a larger binary companion.
White dwarf cooling • Star cools and reddens.
Black Dwarf • Eventually the white dwarf cools off completely and becomes a cold dense ball called a black dwarf because it does not radiate any energy.
Black Dwarf • Star stops glowing.
Now lets talk about massive stars! • Remember, low mass and massive stars for the same way up until the red giant phase. • To be considered massive, a star must be about 8 times larger than our sun.
Massive stars • Massive stars are hot enough to continue to fuse elements until the core becomes iron. • Nuclear reactions in stars can’t make heavier elements than iron.
Supergiant • Star of greater mass expands, cools, and turns red.
Type II supernova • Core releases an explosive shock wave expelling the outer layers of the star in a tremendous explosion called a type II supernova.
Supernova • Supergiant explodes, blasting away outer layers.
After a supernova: option 1 = Neutron Star • Intense pressure in the core causes electrons to fuse with protons creating neutrons.
