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Star Life Cycle

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Michael Morgan
Michael Morgan

Stars are born from clouds of gas and dust called nebulas. As the gas spins faster under gravity, it heats up and forms a protostar. Nuclear fusion then occurs, turning the protostar into a main sequence star that shines for millions of years by fusing hydrogen into helium. Eventually the hydrogen runs out, causing the star to expand into a red giant. From there, less massive stars will blow off their outer layers and collapse into white dwarfs, while more massive stars will explode in supernovas and collapse into neutron stars or black holes.

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The Life Cycle of a StarBy: Michael Morgan
Birth of a StarIn space, there are huge clouds of gas and dust called nebulasThese clouds are made up of hydrogen and helium and are the birthplace of new startsGravity pulls the hydrogen gas in the nebula together and it begins to spinAs the gas spins faster and faster, it heats up and is known as a protostar
ProtostarThe second stage of star creationAt this point the temperature eventually reaches 15,000,000 °C and nuclear fusion occurs in the clouds coreThe cloud begins to glow brightlyAt this stage, it contracts a little and becomes stable and is called a main sequence star
Main Sequence StarA star will remain in this stage, shining for millions or billions of years to comeAs the main sequence star glows, hydrogen in the core is converted into helium by nuclear reactionsOur Sun is a main sequence starAlthough the sun is extremely large compared to Earth, it is only a medium-sized star
Red Giant PhaseWhen the hydrogen supply in the core begins to run out, the core becomes unstable and contractsThe outer shell of the star starts to expandAs it expands, it cools and glows redThe star has now reached the red giant phaseAll stars evolve the same way up to the red giant phase; the amount of mass a star has determines which of the following life cycle paths it will take after the red giant phase
Medium StarsThroughout the red giant phase, the hydrogen gas in the outer shell continues to burn and the temperature in the core continues to increaseAt 200,000,000 °C the helium atoms fuse to form carbon atoms and the last of the hydrogen gas in the outer shell is blown away to form a ring around the core (this ring is called a planetary nebula)When the last of the helium atoms are used up, the medium star begins to die
White DwarfsGravity causes the last of the star’s matter to collapse inward and compact, this is the white dwarf stageAt this stage the star’s matter is extremely denseWhite dwarfs shine with a white hot lightOnce all their energy is gone, they no longer emit lightThe star has now reached the black dwarf phase in which it will forever remain
Massive StarsOnce massive starts reach the red giant phase, the core temperature increasesGravity continues to pull carbon atoms together as the temperature increases forming oxygen, nitrogen, and eventually ironAt this point, fusion stops and the iron atoms start to absorb energyThis energy is eventually released in a powerful explosion called a supernova
SupernovaA supernova can light up the sky for weeksThe temperature in one can reach 1,000,000,000 °CThe supernova then either becomes a neutron star or a black hole
Neutron StarThe core of a massive star that is 1.5 to 4 times as large as our Sun ends up as a neutron star after the supernovaNeutron stars spin rapidly giving of radio wavesIf the radio waves are emitted in pulses (due to the star’s spin), the neutron star is called a pulsar
Black HoleThe core of a massive star that has 8 or more times the mass of our Sun remains massive after the supernovaNo nuclear fusion is taking place to support the core, so it is swallowed by it own gravityIt has now become a black hole which readily attracts any matter and energy that comes near itBlack holes are not visible, they are detected by the X-rays which are given off as matter falls into the hole
Summary

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Star Life Cycle

  • 1. The Life Cycle of a StarBy: Michael Morgan
  • 2. Birth of a StarIn space, there are huge clouds of gas and dust called nebulasThese clouds are made up of hydrogen and helium and are the birthplace of new startsGravity pulls the hydrogen gas in the nebula together and it begins to spinAs the gas spins faster and faster, it heats up and is known as a protostar
  • 3. ProtostarThe second stage of star creationAt this point the temperature eventually reaches 15,000,000 °C and nuclear fusion occurs in the clouds coreThe cloud begins to glow brightlyAt this stage, it contracts a little and becomes stable and is called a main sequence star
  • 4. Main Sequence StarA star will remain in this stage, shining for millions or billions of years to comeAs the main sequence star glows, hydrogen in the core is converted into helium by nuclear reactionsOur Sun is a main sequence starAlthough the sun is extremely large compared to Earth, it is only a medium-sized star
  • 5. Red Giant PhaseWhen the hydrogen supply in the core begins to run out, the core becomes unstable and contractsThe outer shell of the star starts to expandAs it expands, it cools and glows redThe star has now reached the red giant phaseAll stars evolve the same way up to the red giant phase; the amount of mass a star has determines which of the following life cycle paths it will take after the red giant phase
  • 6. Medium StarsThroughout the red giant phase, the hydrogen gas in the outer shell continues to burn and the temperature in the core continues to increaseAt 200,000,000 °C the helium atoms fuse to form carbon atoms and the last of the hydrogen gas in the outer shell is blown away to form a ring around the core (this ring is called a planetary nebula)When the last of the helium atoms are used up, the medium star begins to die
  • 7. White DwarfsGravity causes the last of the star’s matter to collapse inward and compact, this is the white dwarf stageAt this stage the star’s matter is extremely denseWhite dwarfs shine with a white hot lightOnce all their energy is gone, they no longer emit lightThe star has now reached the black dwarf phase in which it will forever remain
  • 8. Massive StarsOnce massive starts reach the red giant phase, the core temperature increasesGravity continues to pull carbon atoms together as the temperature increases forming oxygen, nitrogen, and eventually ironAt this point, fusion stops and the iron atoms start to absorb energyThis energy is eventually released in a powerful explosion called a supernova
  • 9. SupernovaA supernova can light up the sky for weeksThe temperature in one can reach 1,000,000,000 °CThe supernova then either becomes a neutron star or a black hole
  • 10. Neutron StarThe core of a massive star that is 1.5 to 4 times as large as our Sun ends up as a neutron star after the supernovaNeutron stars spin rapidly giving of radio wavesIf the radio waves are emitted in pulses (due to the star’s spin), the neutron star is called a pulsar
  • 11. Black HoleThe core of a massive star that has 8 or more times the mass of our Sun remains massive after the supernovaNo nuclear fusion is taking place to support the core, so it is swallowed by it own gravityIt has now become a black hole which readily attracts any matter and energy that comes near itBlack holes are not visible, they are detected by the X-rays which are given off as matter falls into the hole