The Life Cycles of Stars RVCC Planetarium - Last updated 7/23/03.
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Transcript of The Life Cycles of Stars RVCC Planetarium - Last updated 7/23/03.
![Page 1: The Life Cycles of Stars RVCC Planetarium - Last updated 7/23/03.](https://reader035.fdocuments.in/reader035/viewer/2022062517/56649ee75503460f94bf8d8d/html5/thumbnails/1.jpg)
The Life Cycles of Stars
RVCC Planetarium - Last updated 7/23/03
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Twinkle, Twinkle, Little Star ...
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How I Wonder What You Are ...
Stars have
• Different colors Which indicate different temperatures
• Different sizes
• Different masses
The bigger it is, the hotter and the faster a star burns its life away.
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Stellar Evolution
Stars begin their lives as clouds of gas and dust called Nebulas
Clouds Contain:•70% H•28% He•2% HeavierElements
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Stars start from Nebula Clouds
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Collapse to Protostar
• Nebula compresses
• Gravitational pull attracts more material.
• Temperature and pressure increases
• Nebula shrinks and begins to spin
• Spinning nebula begins to flatten into a disk
….A protostar is formed
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Protostars are forming in Orion
Protostars are forming in the Orion Nebula
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•Pressure builds inside the protostar over millions of years creating heat
•Temp increases to 10 million°C
•Nuclear fusion begins….A star is born!!
•Main Sequence stage of a star begins
•It is the longest stage in life of a star
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Nuclear Fusion !
• At 15 million degrees Celsius in the center of the star, Hydrogen Atoms fuses into Helium.
• It takes 4 Hydrogen atoms to make one Helium atom
• Sun has 1056 H atoms to burn which would last 8 billions year!
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The Beginning of the End: Red Giants
After Hydrogen is exhausted in core:
• Core collapses, releasing energy to the outer layers
• Outer layers expand
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The Core of a Red Giant
•Giants are 10 times bigger than the sun
•Supergiants are 100 times bigger than the sun
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Expansion of the outer Layers
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Betelgeuse – A Red Giant Star
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Outer Layers are Expelled …
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… And a Planetary Nebula forms
Planetary Nebulae
After Helium exhausted, outer layers of star expelled
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Some Planetary Nebulae are Round
As the dead core of the star cools, the nebula continues to expand, and dissipates into the surroundings.
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… and Bipolar
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Some look like an Hourglass …
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.. or a Cat’s Eye …
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… or even look like an Eskimo!
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White Dwarfs
At Center of a Planetary Nebula …
… sits a White Dwarfs
White dwarfs shine for billions of years before they cool completely.
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The Hubble Space Telescope has detected white dwarf stars (circled) in globular clusters:
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White Dwarfs are Small and Heavy
Size of the Earth with the Mass of the Sun
“A ton per teaspoon”
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Nova is a white dwarf star that suddenly increases in brightness by several magnitudes. It fades very slowly.
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Fate of High Mass Stars
• After Helium is exhausted, core collapses again until it becomes hot enough to fuse Carbon into Magnesium or Oxygen.
• Through a combination of processes, successively heavier elements are formed and burned.
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The End of the Line for Massive Stars
• Massive stars burn a succession of elements.
• Iron is the most stable element and cannot be fused further.
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A Massive Star Explodes
A Supernova is an exploding massive star
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Supernova 1987a
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What’s Left After the Supernova
Neutron Star (If mass of core < 5)• Under collapse, protons and electrons
combine to form neutrons.
Black Hole (If mass of core > 5)• The force of contraction crushes the
dense core of the star• The gravity of a black hole is so great
that not even light can escape from it.
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Supernova interaction
This compression starts the collapse of gas and dust to form new stars.
Supernovae compress gas and dust which lie between the stars.
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Which brings us back to …
Sun-like Stars Massive Stars
Stellar Recycling
Nebula
Protostar
Low mass main sequence star
Red Giant
Planetary Nebula
White DwarfNova
High mass main sequence star
Supergiant
Supernova
Neutron Star
Black Hole