Star Life Cycle

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Star Life Cycle
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Stellar Evolution Life of the Star

• The most massive stars have the shortest lives.
  Stars that are 25 to 50 times that of the sun
  live for only a few million years. Stars like our
  Sun live for about 10 billion years. Stars less
  massive than the Sun have even longer life spans
• Stars are like humans they are born, live and die
  
  

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The Birth of Stars
Stars are formed in 1. Nebulae, interstellar
clouds of dust and gas (mostly hydrogen). These
stellar nurseries are abundant in the arms of
spiral galaxies. In these stellar nurseries,
dense parts of these clouds undergo gravitational
collapse and compress to form a rotating gas
globule.
It begins to spin as it shrinks
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NEBULA PICTURES
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Protostar stage The nebula flattens and the
center condenses Temps start to increase due to
friction (more collision of molecules). When
temps reach 10 million K, NUCLEAR FUSION
begins Nuclear Fusion generates the energy for a
star. When fusion begins, it is officially
considered a STAR. (yeah!) Fusion combining a
lightweight nuclei into a heavier nuclei
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Protostar Pictures
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Main-Sequence Stage
The protostar is now a stable main sequence star
which will remain in this state for about 10
billion years. After that, the hydrogen fuel is
depleted and the star begins to die.
Stars live out the majority of their lives in a
phase termed as the Main Sequence. Longest stage
of a star
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Main Sequence Star
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RED GIANT STAGE
When a star has burned between 10 and 20 of its
hydrogen, its core will to run out of fuel. At
this stage, the star is entering the end of its
life.The diameter of the star can increase by a
factor of 200, while its cooling is translated
into a reddening of its radiation the star is
becoming what is called a red giant.
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• Star has run out of Hydrogen atoms in the core to
  undergo fusion.
• Our sun has used only about 5 of its Hydrogen
• Star expands about 10x bigger and cools.
• Its luminosity increases, temp decreases.
• Helium fuses to form Carbon, and the core
  shrinks.
• It begins losing outer layers

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BETELGEUSE RED GIANT
F.Y.I.

• Only a few million years old, Betelgeuse is
  already dying. Astronomers predict that it's
  doomed to explode as a soon, within 1,000 years
  or so, an event that will be spectacular for
  Earth's future inhabitants. (Conceivably, it's
  already happened as Betelgeuse is 640 light-years
  away!)
•  

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• Star size comparison

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Burnout and Death

• Fate of a Star depends on its mass
• All stars, regardless of size, run out of fuel
  and collapse due to gravity
• A star will become either a black dwarf, neutron
  star, or black hole, depending on how massive it
  was. .

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Death of low-mass stars

• Never evolve into red giants
• Remain stable main-sequence stars until hydrogen
  is gone
• Collapse into white dwarfs

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Death of medium-mass stars

• Sun-like Stars
• (Mass under 1.5 times the mass of the Sun)
  Red Giant --gt Planetary Nebula --gtWhite
  Dwarf --gt Black
  Dwarf

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Death of massive stars

• Huge Stars
• (Mass between 1.5 to 3 times the mass of the Sun)
  
• Red SuperGiant --gt Supernova --gt Neutron
  Star
• Giant Stars
• (Mass over 3 times the mass of the Sun)
  Red SuperGiant --gt
  Supernova --gt Black Hole

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PLANETARY NEBULA

• This is left when a giant loses its outer layers
  of gas.
• Leaves only the core.
• The core will become a white dwarf

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Planetary nebula pictures
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WHITE DWARF

• Only hot, dense core is left of this star.
• It will shine for billions of years before
  cooling.
• Stable star with no nuclear fuel,radiates left
  over fuel for billions of years
• Could become a black dwarf, but the universe is
  not old enough to form these

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White Dwarf Pictures

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SUPER NOVA

• Super Giant eventually loses its outer layers in
  an explosion leaving only the core this is the
  super nova.

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Eventually this core collapses (in an instant).
As the iron atoms are crushed together in this
gravitational collapse, the core temperature
rises to about 100 billion degrees.
The repulsive electrical forces between the
atoms' nuclei overcomes the gravitational forces,
causing a massive, bright, short-lived explosion
called a supernova. During the explosion, shock
waves, blow away the star's outer layers.
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NEUTRON STAR

• After a Super Nova explosion, the core may
  condense into a small core of neutrons.
• It is so dense 1 spoonful of Earth would weigh
  100 million tons.
• Rotates very rapidly.
• If the star's remaining mass is between 1 1/2 to
  3 times the mass of the Sun, it will collapse
  into a small, dense neutron star (about ten miles
  in diameter, about 1.4 times the mass of the Sun,
  with an extraordinarily strong magnetic field,
  and rapid spin).

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Neutron Star Pictures

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BLACK HOLE

• This is the 3rd predicted result to a star.
• This is the most dense core of a star that can be
  left.
• Gravity is so strong, light cannot escape.
• Makes it look like a dark hole in space.
• If the star's remaining mass is greater than
  three times the mass of the Sun, the star
  contracts tremendously and becomes a black hole

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Black Hole Pictures

Anatomy of a black hole
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• The density of a star is pre-determined based on
  its weight (the amount of dust and gas) it begins
  with.
• Smaller stars become white dwarfs.
• Very large stars become neutron stars or black
  holes.

• Life Cycle of a Star Video