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

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slide1

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

learning environment
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

objectives
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

controls
Controls
  • Home Button
  • Highlighted Text
  • Back One Slide
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astronomy the life cycle of star
Astronomy:The Life Cycle of Star

Table of Contents

Main Menu

slide6

Main Menu

  • Study Guide
  • Quiz
  • Keywords
table of contents
Table of Contents
  • Birth of a Star
  • Main Sequence Stage
  • Types of Stars
  • Zones of a Star
what is stellar evolution
What is Stellar Evolution?
  • Stellar Evolution is the life cycle of a star and the processes that it will undergo throughout its life
what is a star
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)
gravitational collapse
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)
slide11

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
slide12

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
what is next
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
main sequence stage
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
slide16

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
slide17

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
slide18

Choose one to explore the life cycle of that type of star

Low-Mass Star

Mid-Size Star

High-Mass Star

low mass star
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
mid size stars
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)
slide22

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
slide23

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
red giant
Red Giant

Planetary Nebulae

massive stars
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)
sounds like a contradiction
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
slide27

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
nuetron stars
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
black holes
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
slide32

1. Corona

  • atmosphere of a star”
slide33

2. Chromoshpere

  • Visible during a total eclipse of a star
slide34

3. Photoshpere

  • About 10,000 degrees Kelvin
  • The visible layer that we “see”
slide35

4. Convection Zone

  • Layer just below the surface where all the stars material is in constant motion via convection
slide36

5. Radiation Zone

  • Extremely high temperatures allow gas to be copleteley ionized
slide37

6. Core

  • Almost 17 million degrees Kelvin
  • center of the star”
an acronym to remember
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
slide39

Quiz

Table of Contents

Keywords

Home

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

Begin

protostar
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
proton proton chain
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
main sequence star
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
luminosity
Luminosity
  • Candela/ per Square Meter
  • How bright the star actually is, not how bright it appears to be to the naked eye
solar masses
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
white dwarf
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!!!
cno cycle
CNO Cycle
  • Carbon-Nitrogen-Oxygen cycle
  • How massive stars obtain hydrostatic equilibrium
  • Usually occurs in stars above 3.3 solar masses
quiz time
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

slide49

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.

slide50

Correct!!!

Next Question

incorrect
Incorrect!!!

Try again.....

2 true or false
2. True or False?
  • Stars form from the expansion of a cloud of space dust

True

False

slide53

Correct!!!

Next Question

incorrect1
Incorrect!!!

Try again.....

3 a more massive star
3. A More massive star:

a. Live longer than low-mass stars.

b. Die and Create a black hole or neutron star.

c. Have shorter lives than main sequence stars.

d. A and C

e. B and C

slide56

Correct!!!

Next Question

incorrect2
Incorrect!!!

Try again.....

4 the order of layers of a star from outermost to innermost is
4. The order of layers of a star from outermost to innermost is:

a. Convection, Corona, Core, Photoshpere

b.Photoshpere, Chromoshpere, Corona, Core

c. Corona, Chromoshpere, Photoshpere, Convection, Radiation, Core

d. Convection, Radiation, Photoshpere, Chromoshpere, Corona, Core

slide59

Correct!!!

Next Question

incorrect3
Incorrect!!!

Try again.....

5 low mass stars that die before they begin the proton proton chain become
5. Low-mass stars that “die” before they begin the proton-proton chain become:

a.Supergiants

b. White Dwarfs

c. Brown Dwarfs

d. Neutron Stars

slide62

Correct!!!

Finish Study Guide

incorrect4
Incorrect!!!

Try again.....

congradulations
Congradulations!!!

You have completed the study guide!!!!