The Death Of a Star

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The Death Of a Star

• Ask not for whom the bell tolls,
• it tolls for thee

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How do we know stars die?

• HR Diagrams reveal different types of stars.
• How did they get there?
• Physics tells us how stars work.
• Luminosity depends on mass (LM4) (Gas)
• Fusion principles (4 H ? 1 He) tell us the rate
  stars use energy. (kinda like MPG on a car.)
• Stars will run out of fuel. (the dial goes to
  E)

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Gravity

• Every star fights a battle.
• Gravity force pulling the star together.
• Fusion force pushing the star apart.
• Most stars find a balance.
• Some stars are never balanced
• Cephids pulse as they growlarger and smaller.

Fusion
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Cepheus
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A stars fate is chosen at birth

• The outcome of the battle is determined by
  gravity and gravity means

Mass
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Three paths
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Small Stars

• Small stars last longer (dont consume fuel as
  quickly)
• Main sequence on HR diagrams.
• Burn hydrogen for most of their lifetime.

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Red Giants

• As star runs out of hydrogen, the core cools
• Gravity starts to win --gt shrinkage in core.
• Increased pressure starts Helium fusion
• 150 Million K
• Carbon Oxygen Products
• Hotter temperature makes outer part of star
  expand yet.
• Expanded surface is actually cooler so appears
  red

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Red Giants

• Stars less than 1.4 Solar Masses
• Gravity is weak
• Outer layers eventually puff off - not enough
  gravity
• Planetary nebula forms from gas
• White dwarf remains

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If its a cloud, why does it look like a ring?
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Cats Eye Another Planetary Nebula
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White Dwarfs

• Carbon/Oxygen
• Matter is compressed
• One teaspoon a pickup truck
• Electron/quantum pressures balance gravity
• Very Hot 30,000K to 200,000 K
• Slowly Cool to Black Dwarfs
• So slow, none exist yet.
• Except this guy ?

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White Dwarfs
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Red Supergiants

• Stars more than 1.4 Solar Masses
• Gravitational Core Energy Reaches 150 Million K
• Carbon turns to Mg, O, N
• With enough mass, even heavier elements fused
• At each step, less and less energy yielded --gt
  shorter duration
• Star keeps getting bigger!
• Iron is the end of the road.

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The most famous S-G
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Fusion Layers in a Supergiant
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Why Stop at Iron??
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Review
Mass

• ______ determines the fate of a star.
• The two forces acting on a star are ____ and
  _____
• When a star reaches the end of its life it begins
  to fuse ______ and it ______.
• When fusion stops a typical star will produce a
  __ and become a ______ _____.
• Even the largest stars cant fuse elements
  heavier than _____.

gravity
fusion
helium
swells
planetary nebula
white dwarf
iron
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The party is over

• Once iron is in the core, outwards pressure
  ceases
• Core collapses at 1/4 the speed of light takes
  about 1/10 of a second
• Collapse of the core to about 100 km across
• Outer layers bounce of the solid core
• Releases 100x the energy of our sun produces in
  its lifetime -- in 1/10 of a second!!!

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A supernova

• Note the before / after differences
• 1987A

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After the party

• Lots of neutrons hanging out during this
  explosion
• Neutrons hook - up with lighter elements making
  heavy elements
• Calcium, Gold, Zinc, Uranium, etc
• Forget Hollywood .. We are all stars!!!

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Aftermath

• After a supernova explosion you can wind up
  several possibilities
• Nebula Neutron Star
• Nebula Pulsar
• Black Hole

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Nebula

• Clouds of material left from the explosion
• The Primordial Goo for new stars, planets,
  people!

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Supernova 1987

• Very complicated structure
• Nearby star affecting the cloud

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Our new neighbors?
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Neutron star

• Forms if the remaining core is between 1.4 and 3
  times the suns mass
• All this mass in the size of Schaumburg!
• One teaspoon gt The Sears Tower
• All available space in the atom (which is
  99.9999 space) is removed.

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Neutron Star
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Pulsar

• Neutron star that spins.
• Spinning magnetic field channels radiating energy
  into beams.
• If this beam isnt always pointing at us - it
  flashes like a lighthouse.
• First Pulsar was mistaken as alien communication

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A Pulsar
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Black Holes

• Remaining Core is more than 3x the sun.
• Gravity overcomes everything, neutrons vanish
• Matter in the core overlaps a singularity
• Gravity prevents light from escaping.--gt Black
  Hole
• Closest light can get without being trapped
  Event Horizon
• 3 S.M star 55km E.H. (Chicago?)
• Earth as a black hole? Compress it into a marble!

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Finding Black Holes

• May pull matter off a nearby star - Accretion
  Disk X-Rays
• Immense mass in the center of galaxies

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A trip to a black hole

• Pretty Short
• Difference in gravity between your head and feet
  literally pull you apart.
• Once you hit the E.H. you arent coming back.
• Everything you are is crushed into a single point
  - you no longer exist
• No one would see you enter the Black Hole because
  time stands still at the edge.

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Black Holes - Expert Testimony
Black Holes More Expert Testimony