Life Cycle of a Star

8.8A describe components of the universe, including stars, nebulae, and galaxies, and use models such as the Herztsprung-Russell diagram for classification.

ENGAGE: Life Cycle of a Human

• Humans change through time. Describe the Life Cycle of a Human

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-Record at least 4 Stages in your Notebook.

-Include the length of the stages and important details about each stage.

Human Life Cycle

EXPLAIN: Life Cycle of STARS

Use pg 258-259 to illustrate the Life Cycle of a Star.

• record information about each phase from slides.

Life Cycle of a Star

• The changes that a star goes through is determined by how much mass the star has.

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Two Types of Life Cycles:

Average Star- a star with relatively low mass

Massive Star- a star with relatively high mass

Life Cycle of Stars

http://www.seasky.org/cosmic/sky7a01.html

Stellar Nebula

• All stars begin in a cloud of gas and dust called a stellar NEBULA.
• Gravity will cause the nebula to contract.

The nebula will break into smaller pieces. These pieces will eventually form stars.

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The Life of an Average Star

• An Average Star (low mass star) is condensed in a nebula and begins a nuclear reaction that causes hydrogen to form helium, releasing energy in the form of heat and light.
• A low mass star will stay in this MAIN SEQUENCE phase for a long time, until it begins to use up all of it’s hydrogen.

The Life of an Average Star

• Towards the end of it’s MAIN SEQUENCE phase, a star begins to burn all of its hydrogen.
• The outer layers will collapse, become heated by the core and expand out forming a red giant.

The Life of an Average Star

• The star begins to quickly blow off its layers forming a cloud around the star called a planetary nebula.
• The star in the center of the nebula is very hot but not very bright.

The Life of an Average Star

• When a star has burned all it’s fuel it will collapse under the pressure of gravity.
• The white dwarf that forms is very small and dense.

Life of a Massive Star

http://www.seasky.org/cosmic/sky7a01.html

Stellar Nebula

Stellar Nebula

• All stars begin in a cloud of gas and dust called a stellar NEBULA.
• Gravity will cause the nebula to contract.

The nebula will break into smaller pieces. These pieces will eventually form stars.

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Life of a Massive Star

• Stars with more mass than the sun (high mass stars) burn their hydrogen faster than low mass stars, so their MAIN SEQUENCE phase is much shorter.
• These stars burn hotter and brighter than low mass stars.

Life of a Massive Star

• When the high mass star burns off it’s hydrogen its outer layers begin to expand rapidly.
• Temperatures at the core are much higher than a red giant. Nuclear fusion causes elements to combine into an iron core at amazing speeds.

Life of a Massive Star

• The iron core collapses on itself under the intense gravity at very high speeds.
• The energy released is called SUPERNOVA.

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Life of a Massive Star

• After the incredible release of energy from the SUPERNOVA a dense core (1 trillion times denser than a white dwarf) is all that remains of the Massive Star.
• If the mass is too dense it will continue to collapse on itself forming a black hole. The gravitational pull of a black hole is so great, light can not escape.

The Hertzsprung-Russell (HR) Diagram

MAGNITUDE: Brightness Increases from bottom to top

REMEMBER: Temperature Increases from right to left

1 L is equal to the brightness of the sun

Are these stars brighter or dimmer than the sun

The Hertzsprung-Russell (HR) Diagram

Characteristics of Stars

• Temperature & Color
• The color of a star indicates the T of the star
• Stars are classified by T
• Decreasing T (bright to dim)
• O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss Me ]

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http://www.seasky.org/cosmic/sky7a01.html

The Hertzsprung-Russell (HR) Diagram

http://www.dustbunny.com/afk/stars/lifecycle/hrdiagram.gif