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4.2 Stars have Life Cycles

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Emily Hudak
Emily Hudak

Stars change over their life cycles depending on their mass. Low-mass stars like our Sun remain on the main sequence for billions of years, slowly fusing hydrogen into helium. Eventually they expand into red giants and later cool into white dwarfs. High-mass stars burn through their fuel quickly and explode as supernovae after millions of years, leaving behind neutron stars or black holes. All stars form from contracting nebulae of gas and dust.

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Stars changed over their life cyclesSpace Science:Chapter 4: Section 4.2
Let’s BeginWhy do stars look like small points of light?Why don’t they look like in the sky?Stars are very far away.We only see a few thousand of stars that exist.
What unit of measurement do we use to measure the distance between stars?Light-yearsThe distance light travels in one yearApproximately 6 trillion milesThe closest star to Earth is our SunThe next closest star is 4 light years away
How do we measure how far stars are away from Earth?Using parallaxThe apparent shift in the position of an object when viewed from different locationsParallax Demonstrations
Size: the Sun’s diameter is 100x greater than Earth’s
Some stars are much larger than the Sun. Giant and Super giants are 10-100’s of times larger.
Betelgeuse: 600 times greater than the Sun
There are stars much smaller than the Sun as well. These are called white dwarfs.
What color are the stars we see?Most stars are whiteSome appear redSome appear blueWhy is that?Differences in color are due to differences in temperature
Think of:The metal coils inside of a toasterStart off as a dull redLater turn a bright orangeTemperature affects color by heating up the metal
Stars have life cycles:Length of the cycle and the way a star changes depends on the mass of the star
Nebula:All stars form inside a cloud of gas and dust called a nebulaGravity pulls the dust closer togetherThe matter contracts and forms a hot dense sphere
Main Sequence:Fusion begins if the matter gains enough temperature and densityThe birth of main sequencestars
Low-Mass Stars:Once fusion begins the star is then classified as a main sequence starLow-mass stars use their fuel slowlyRemain in this stage for billions of yearsAs low-mass stars run out of fuel it expands into a giant starOnce the giant sheds it outer layer it leaves behind a dead core called a white dwarf
4.2 Stars have Life Cycles
High-Mass Stars:Once fusion begins the star is then classified as a main sequence starHigh-mass stars use their fuel quicklyRemain in this stage for millions of yearsAs high- mass stars run out of fuel it expands into a super giant The super giant explodes when no more fusion can occur- called a supernova
4.2 Stars have Life Cycles
High-Mass Stars: After supernovaMay form a dense body called a neutron starStar squeezes itself smallerVery DENSE- Example: pea size sample weighs 100 million tonsGravitational force collapses atomsElectrons combined with protons to produce neutronsMay form a black holeMore dense than neutron starIntense surface gravity lets no light escapeAs matter is pulled into the black hole it becomes very hot and emits x-rays
4.2 Stars have Life Cycles
The Sun is what type of star?Low-MassMain Sequence StarWhat is going to happen to the Sun?Eventually expand into a Red GiantCool down into a white dwarfScientist predict that in 4.5 billions years the Sun will run out of fuel and will form a Red Giant
4.2 Stars have Life Cycles

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4.2 Stars have Life Cycles

  • 1. Stars changed over their life cyclesSpace Science:Chapter 4: Section 4.2
  • 2. Let’s BeginWhy do stars look like small points of light?Why don’t they look like in the sky?Stars are very far away.We only see a few thousand of stars that exist.
  • 3. What unit of measurement do we use to measure the distance between stars?Light-yearsThe distance light travels in one yearApproximately 6 trillion milesThe closest star to Earth is our SunThe next closest star is 4 light years away
  • 4. How do we measure how far stars are away from Earth?Using parallaxThe apparent shift in the position of an object when viewed from different locationsParallax Demonstrations
  • 5. Size: the Sun’s diameter is 100x greater than Earth’s
  • 6. Some stars are much larger than the Sun. Giant and Super giants are 10-100’s of times larger.
  • 7. Betelgeuse: 600 times greater than the Sun
  • 8. There are stars much smaller than the Sun as well. These are called white dwarfs.
  • 9. What color are the stars we see?Most stars are whiteSome appear redSome appear blueWhy is that?Differences in color are due to differences in temperature
  • 10. Think of:The metal coils inside of a toasterStart off as a dull redLater turn a bright orangeTemperature affects color by heating up the metal
  • 11. Stars have life cycles:Length of the cycle and the way a star changes depends on the mass of the star
  • 12. Nebula:All stars form inside a cloud of gas and dust called a nebulaGravity pulls the dust closer togetherThe matter contracts and forms a hot dense sphere
  • 13. Main Sequence:Fusion begins if the matter gains enough temperature and densityThe birth of main sequencestars
  • 14. Low-Mass Stars:Once fusion begins the star is then classified as a main sequence starLow-mass stars use their fuel slowlyRemain in this stage for billions of yearsAs low-mass stars run out of fuel it expands into a giant starOnce the giant sheds it outer layer it leaves behind a dead core called a white dwarf
  • 16. High-Mass Stars:Once fusion begins the star is then classified as a main sequence starHigh-mass stars use their fuel quicklyRemain in this stage for millions of yearsAs high- mass stars run out of fuel it expands into a super giant The super giant explodes when no more fusion can occur- called a supernova
  • 18. High-Mass Stars: After supernovaMay form a dense body called a neutron starStar squeezes itself smallerVery DENSE- Example: pea size sample weighs 100 million tonsGravitational force collapses atomsElectrons combined with protons to produce neutronsMay form a black holeMore dense than neutron starIntense surface gravity lets no light escapeAs matter is pulled into the black hole it becomes very hot and emits x-rays
  • 20. The Sun is what type of star?Low-MassMain Sequence StarWhat is going to happen to the Sun?Eventually expand into a Red GiantCool down into a white dwarfScientist predict that in 4.5 billions years the Sun will run out of fuel and will form a Red Giant