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. Essential Questions 1. How do stars change over time? 2. How are stars classified on a Herztsprung-Russell Diagram? 3. How does our sun compare to other stars in the universe? Objectives 1. Describe objects in space such as stars (in all life stages) and galaxies. 2. Describe the life cycle of a star and correlate a star’s life stage to its placement on the HR-Diagram. 3. Classify the types of stars on the HR- Diagram.

Human Life Cycle

Space School: Stars Stars

EXPLAIN: Life Cycle Foldable Use pg 717 to illustrate your Life Cycle Foldable. Read pgs to record information about each phase. NebulaAverage Star (low mass star) Red GiantPlanetary Nebula White Dwarf NebulaMassive Star (high mass star) Super Red Giant SupernovaNeutron Star or Black Hole

Life Cycle of a Star The changes that a star goes through is determined by how much mass the star has. 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

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.

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

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.

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 it’s self under the intense gravity at very high speeds. The energy released is called SUPERNOVA.

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.

Warm Up: Read to Learn Read page 706 in your textbook. -In your journals use the word Brightness in a sentence. -In your journals use the word magnitude in a sentence.

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 ]

The Hertzsprung-Russell (HR) Diagram