Learning Environment

1. This guide will discuss the life cycle of a star (stellar evolution). Throughout the guide, pay attention to highlighted words, they may be on the quiz

2. Learning Environment Students will only need a computer lab or home desktop/laptop to complete this study guide and quiz Grades 9-12 For individual learning Target Audience

3. Objectives Students will learn about the life and death of stars, and upon completion of this study guide, be able to identify layers of a star and other material contained in this study guide with 80% accuracy

4. Controls • Home Button • Highlighted Text • Back One Slide • Next Slide

5. Astronomy:The Life Cycle of Star Table of Contents Main Menu

6. Main Menu • Study Guide • Quiz • Keywords

7. Table of Contents • Birth of a Star • Main Sequence Stage • Types of Stars • Zones of a Star

8. What is Stellar Evolution? • Stellar Evolution is the life cycle of a star and the processes that it will undergo throughout its life

9. What is a Star? • Stars form from dense molecular clouds, also known as GMCs (Gaseous Molecular Clouds) • The cloud becomes so large, the force of gravity is extremely intense • The GMC collapses in on itself with a massive amount of pressure (this is known as gravitational collapse)

10. Gravitational Collapse? • The collapsing gas implodes with so much pressure, it creates a massive amount of heat and energy (similar to more friction = more heat) • The core of the GMC is so hot and dense, gravity takes over and it begins to spin • This is called a protostar (like a baby star)

11. The faster the protostar spins, the hotter it becomes • Once the internal temperature reaches 10 million Kelvins,the proton-to-proton chain reaction begins • At this point, the hydrogen (H) molecules in the core begin to fuse with the helium (He) molecules

12. If the protostar‘s temperature never begins the proton-proton reaction, it become what is know as a brown dwarf • Essentially this is known as a dead star • Over hundreds of thousands of years it will slowly cool and become dimmer and dimmer

13. What is Next? • Once the star’s internal pressure pushing outwards equals the force of gravity pushing inwards, the star reaches the stage known as hydrostatic equilibrium • The outward pressure is created by more and more molecules fusing, creating more heat • Example: a balloon in a cold room versus a balloon in a hot room (hot one expands more, creating more outward pressure) • The star then enters the Main Sequence stage of its life

14. Main Sequence Stage • Depending on the mass of the star, it can remain a Main Sequence (M.S.) star for an extremely long time • Larger stars burn up their “fuel” faster, thus remain a main sequence star for shorter amounts of time

15. This the Main Sequence Chart (also known as the Hertzsprung-Russell diagram)

16. M.S. stars are placed on the Hertzsprung-Russell Diagram according to luminosityand temperature • The brighter the star, the hotter it is, less heat = less luminous

17. Depending on the size of the star, it may go through its life cycle and end up as many different things • Smaller stars become white dwarfs eventually • Larger stars can become supernovas, black holes, or neutron stars

18. Choose one to explore the life cycle of that type of star Low-Mass Star Mid-Size Star High-Mass Star

19. Low Mass Star • Stars smaller than .05 solar masses will die when they have used up their supply of hydrogen molecules • Not all low mass stars become large enough to reach the main sequence stage • When they use all the hydrogen, they collapse in again and create a white dwarf

20. A White Dwarf Star

21. Mid Size Stars • Range from 1.4 solar masses to 10 solar masses • Depending on the size of the star, it will live longer • Mid size stars, like our sun, can survive for millions of years • As a star reaches its end, the core heats rapidly and the outer layers expand away from the core (in effect the star begins to swell)

22. The hotter the internal temperature gets, the more force the outer layer are pushed outward with (the bigger the star the more force the layer are pushed out with) • The further the layers get from the core, the cooler they become • Once expansion of the cooling outer layers stops, they become a reddish color • A star in this stage is known as a red giant

23. The farther the layers get from the core, the less gravity they have holding them to the star • Eventually they will get pulled off of the star and be dispersed back into space • This forms planetary nebulae • Eventually, the core implodes and forms a white dwarf

24. Red Giant Planetary Nebulae

25. Massive Stars • Use the CNO cycle instead of the proton-proton chain to maintain equilibrium • Range from 15 solar masses to 115 solar masses (most massive, like VY Canis Major) • They are so large, they are not usually main sequence stars • Smaller massive stars outer layer expand and cool just like some main sequence stars • Even though these stars are cooler than some smaller stars, they are brighter (more heat = brighter star)

26. Sounds like a Contradiction… • It seems incorrect that if heat creates a brighter star, how can a cooler star be brighter? • Example: • Two side by side 100 watt light bulbs compared to 10 side by side 75 watt bulbs • Less powerful bulbs, but based on pure wattage the 10 bulbs are brighter • Massive stars are cooler, but they have so much surface mass creating the light, they are brighter

27. Massive star end their lives in one of two ways: neutron stars or black holes • The star is so large, when it dies the sheer mass collapsing in on itself can turn the protons inside the star into neutrons, forming a star made completely of neutrons • It the star is a large massive star, it will explode, and then collapse in back on itself with so much force and pressure that gravity will never take hold, and the star will continue to collapse forever, creating a black hole

28. Nuetron Stars • Neutron stars are extremely small (in star terms) • They are usually about 10km across, the size of a small city • They are super dense and spin at about 600 revolutions per second

29. Black Holes • 2-3 solar masses in size • Black holes can’t actually be seen through a regular telescope • Scientists can only detect them in one of 2 ways: super nova remnant or a black hole “sucking up” matter from a nearby star or space gas • Before a black hole is created, it is preceded by a supernova (major expansion just before the implosion, like a “cosmic bomb”) that disperses the stars outer layers (cosmic matter) back into the universe

30. A black hole “sucking up” cosmic matter from a nearby star

31. Zones of a Star

32. 1. Corona • atmosphere of a star”

33. 2. Chromoshpere • Visible during a total eclipse of a star

34. 3. Photoshpere • About 10,000 degrees Kelvin • The visible layer that we “see”

35. 4. Convection Zone • Layer just below the surface where all the stars material is in constant motion via convection

36. 5. Radiation Zone • Extremely high temperatures allow gas to be copleteley ionized

37. 6. Core • Almost 17 million degrees Kelvin • center of the star”

38. An Acronym to Remember • When you are trying to remember the different zone of a star, try to remember these two words: • Co/Ch/pho Con/ra/Core = Corona, chromoshpere, photoshpere, Convection Zone, Radiation Zone, Core

39. Quiz Table of Contents Keywords Home

40. Keywords • Protostar • Proton-Proton Chain • Main Sequence Star • Luminosity • Solar Masses • White Dwarf • CNO Cycle Begin

41. Protostar • When a GMC collapses in on itself, then stabilizes through hydrostatic equilibrium. • This is how a star is born, so you could say a protostar creates a baby star

42. Proton-Proton Chain • Process of fusing hydrogen to helium atoms at the core of a star • Occurs in low to mid-mass stars • What causes the stars collapse to stop and allow it to become balanced

43. Main Sequence Star • A graph (also known as the Hertzsprung-Russell Diagram) that plots a star based on color and brightness • Where a star is placed on this graph can tell you how long it will “live” and what it looks like to the naked eye

44. Luminosity • Candela/ per Square Meter • How bright the star actually is, not how bright it appears to be to the naked eye

45. Solar Masses • A unit used to describe stars size • Based on the size of our sun (1 sun = 1 solar mass) • Example: A star of 1.9 solar masses is 1.9 times bigger than the sun

46. White Dwarf • Final evolutionary stage of a star that did not have enough mass to become a supernovae or neutron star • White dwarfs are so dense they are about the mass of the sun crammed into a star remnant the size of the Earth!!!

47. CNO Cycle • Carbon-Nitrogen-Oxygen cycle • How massive stars obtain hydrostatic equilibrium • Usually occurs in stars above 3.3 solar masses

48. Quiz Time!!! You will now be quizzed over some of the keywords and material in the study guide. Hope you were paying attention!! (click on the letter of the answer, not the words) Begin

49. 1. What is Stellar Evolution? a. Life of a star and the processes that it undergoes. b. Evolution from birth to death of the universe. c. How a star is created. d. The age of a star.

50. Correct!!! Next Question