George Observatory

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George Observatory The Colorful Night Sky
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A Stars Lifespan depends on its Mass
Massive Stars live shorter lives. Low mass stars
live longest. 1.Gravity contracts the Hydrogen
gas 2. Gas Spins 3. Gas Heats 4. Protostar
Stage 5. Fusion begins in the clouds
core 6. Cloud glows brightly 7. Main Sequence
Star
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Star Birth
Hydrogen collects in the center of the swirling
disk .
Gravity pulls the densest pockets of hydrogen gas
inward
The Gas spins faster, and heats up.
The cloud begins to shine brightly, a young star
is born in the cloud
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Star Birth
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Sun Like Star Long Lifetime
The protostar is now a stable main sequence star
. Gravity pulls in Pressure pushes out Star is
in balance Neither shrinks or expands Yellow
shining mass
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The Sun is a Main Sequence Star
It fuses hydrogen gas into helium Lifetime 10
billion years. Near the end - hydrogen fuel is
depleted and the star begins to die.
Our Sun is considered to be an ordinary star with
a spectral classification of G2 V, a yellow dwarf
main sequence star.
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Sun Like Stars how do they do it?

• In the stars core protons collide and stick
  together with a strong nuclear bond.
• A chain reaction occurs, 4 protons weld together
  to make 2 protons 2 neutrons.
• Hydrogen converts to Helium through nuclear
  fusion.
• Every second the Sun through thermonuclear
  reaction converts 600 million tons of hydrogen
  into Helium within its core and emits a tiny
  fraction of energy EMC2,
• the radiation escapes into space bathing the
  stars surroundings in heat and light.
• This is what warms our solar system

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Red Giant Phase
As the Sun ages, Eventually, the Supply of
hydrogen in the core ends, and a shell of
hydrogen surrounds the helium core. The Suns
core becomes unstable The helium core contracts
and gets hotter.
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Red Giant star seen from a planet
The Suns hydrogen shell expands The Sun is now
a Red Giant Hydrogen in the shell around the
core continues to burn Its core temp continues to
increase
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Red Giant Phase

• Now the Helium core contracts
• When the Hydrogen shell ignites
• The shell continues to push outward
• Sun becomes enormous
• It goes from
• 1 million to 100 million miles in size

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Red Giant Phase

• Helium ignites, it starts to fuse into Carbon and
  Oxygen. The core collapses.
• The outer layers are expelled.
• It becomes a brilliant cool variable star for
  thousands of years like Betelgeuse in Orion.

Actual photograph of Betelgeuse
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Eventually all of the hydrogen gas in the outer
shell of the Red Giant is blown away by stellar
winds to form a ring around the core. This ring
is called a planetary nebula. The core is now a
hot white dwarf star.
Red Giant becomes a White Dwarf star
A white dwarf star is left in the center of the
dying red giant star, surrounded by the red
giants expanded atmosphere
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Death of a Sun like star White dwarf to black

• A White dwarf star is a dense stable star about
  the size of the Earth weighing three tons per
  cubic centimeter.
• It radiates its left-over heat for billions of
  years.
• When its heat is all dispersed, it will be a
  cold, dark black dwarf - essentially a dead star

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Death of a Massive Star
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Massive Stars
When massive stars ( At least 5 times larger than
the Sun) reach the red giant phase, their core
temperature increases because carbon is formed
from the fusion of helium. Gravity pulls carbon
atoms together. The core temp goes higher
forming oxygen, then nitrogen, and eventually
iron.
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SuperNova Explosion

• The core becomes iron, fusion stops. No energy.
• Iron is the most stable element and requires the
  most energy of any element to fuse.
• So, the core heats to 100 billion degrees, the
  sudden lose of energy causes the core
• to collapse
• The iron atoms in the core are crushed.
• The core becomes rigid.
• In falling layers of the star strike the core,
• then recoil in a Shockwave.
• The shockwave hits the surface and the star
  explodes.

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Supernova
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SuperNova Explosion
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If the core of a massive star collapses when it
is 1.5 to 3 times as massive as our Suns core.
It ends up as a neutron star. The protons and
electrons are squeezed together by gravity,
leaving a residue of neutrons, creating a neutron
star.
Neutron Stars
Neutron stars (right) are about ten miles in
diameter. Spin very rapidly (one revolution takes
mere seconds!). Neutron stars are fascinating
because they are the densest objects known except
for black holes. A teaspoon of neutron star
material weighs 100 million tons.
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Extremely Massive Stars
Massive Stars (8 times or more larger than the
Sun. Core remains massive after the
supernova. Fusion is stopped. Nothing supports
the core. The core is swallowed by its
gravity. It becomes a black hole Black holes
are detected by X-rays given off matter that
falls into the black hole.
become black holes
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Black Holes