The Life of a Star (15.1) BLM 15.1b

1. The Life of a Star(15.1)BLM 15.1b

2. The Life of a Star(p. 468) We say that stars have a “life” because they form from clouds of gas and dust and follow a predictable series of stages: • they begin (“birth”) • they develop • they end (“die”). Each life might take billions of years or more.

3. Three types of Stars There are three types of stars: Dwarf (same or less mass than the sun) - 95% The sun is actually a dwarf. Giant (10 times the mass of the sun) – 4% Supergiant (30 times the mass of the sun) – 1%

4. Birth All stars begin their lives as nebulas, which are huge clouds of dust and gases, mainly hydrogen and helium. As they swirl around, the dust bumps into each other and forms larger and larger clumps.

5. Early Life When clumps have enough hydrogen and dust – nuclear fusion starts. They have become new stars. They get hotter and hotter from the nuclear fusion. You would think that the larger a star is the longer it would live, this is not true.

6. Life of Stars Dwarf stars undergo nuclear fusion for about 10 billion to 100 billion years. (not bright at all) Giant stars produce energy for a few million years. (5000x’s as bright as the Sun) Supergiant stars produce energy for about a million years. (extremely bright) Giant and Supergiant stars use their energy faster. This is why they are brighter and don’t last as long.

7. Old Age When a star nears the end of its life it starts to use the last of it’s hydrogen fuel and swell slightly larger as pressure reduces and turns red (cools down).

8. Supernova A supernova is an enormous final explosion of a star as it uses up the last of it’s fuel. The center of the star collapses inward to become either a neutron star or a black hole. The outer layers of the star explode and the gas and dust are pushed outwards.

9. What is left? Dwarf stars - cool and fade away. Giant stars - the core packs together as a neutron star. An extremely dense star composed of neutrons. Supergiant stars - the core packs together as a black hole. A small, very dense object with a force of gravity so strong that nothing can escape from it. Even light cannot get away from its surface so they can exist undetected.

10. Summary See page 469 in your text. Handout BLM 15.1b.

12. Summary

13. Questions p. 471 1. Describe how a star forms. Stars form from huge clouds of dust and gases called nebulas. The dust and gases swirl around, forming clumps. These clumps attract each other because of gravity and grow larger and larger. When they are large and dense enough, they begin to produce large amounts of light energy and other forms of energy.

14. Questions p. 471 2. Describe the differences between the life of a low-mass star and that of a star 10 times the Sun’s mass. Low-mass stars cool down and swell up into a red giant. Outer layers drift away and the star shrinks to become a white dwarf which will cool and fade away. High-mass stars swells into a red supergiant which undergoes a supernova. This leaves behind either a neutron star or a black hole depending on the mass of the original star.

15. Questions p. 471 3. What is a supernova? A supernova is a type of explosion that occurs when the source of energy of a high-mass star is used up. The outer layers of the star expand outward rapidly.

16. Test Review Questions Ch.13: 13.1, 13.3, 13.4 p. 434-435: Questions 7, 11. Ch. 14: 14.7, 14.10, 14.11 p. 464-465: Questions 3a, 8-10, 11-14. Ch.15: 15.1 p. 484-485: Questions 2-4, 6-8.

17. Topics by section: 13.1: Basic Terms, How planet’s move, Key differences between planets and stars. 13.3: Rotation vs. Revolution, How does this relate to the Earth’s days, years, seasons. 13.4: Constellations – know how to locate on a star map. 14.7: Composition of the Sun, Parts of the Sun, How the Sun’s energy is made. *14.10: 5 key characteristics of the Sun: Colour, Size, Temperature, Brightness, and Spectrum. 14.11: 4 Types of Galaxies, Which is ours? *15.1: Stages of the life of a star, Know a little about each stage.