High mass endings

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High mass endings
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Answers from you folks on yesterdays quiz.

• Differences between a dying low mass vs. a dying
  high mass star
• No He flash in a high mass star death.
• Low mass stars end in white dwarfs, high mass
  stars end in supernovae.
• Heavy elements formed in death sequence of a high
  mass star.
• Low mass stars end in white dwarfs with planetary
  nebulae around them.
• The weight watcher rule big things go early,
  smaller things live longer.

Good Job. Folks !!!!!!
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Large mass stars and the main sequence

• What do they do on the main sequence?
• CNO cycle Carbon, nitrogen, oxygen cycle
• High temperatures needed for this cycle to take
  place ( 15 million 0K).
• H is used along with C as a catalyst to produce
  He atoms.

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Large mass stars on the main sequence continued

• 3. Stay stable hydrostatic equilibrium
• Main Sequence turn-off
• Almost the Same as with low mass star
• Depletion of H in core
• He core contracts
• Temperatures rise igniting H layer
• Increased pressure drives envelope of star
  outward creating a super giant or giant.
• This cycle repeats many times depending on mass.
• When it does, at each new stage heavier elements
  are created.

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Fusion of heavy elements.

• As temperature increases with depth, the ash of
  each burning stage becomes the fuel for the next
  stage.
• So as each element is burned to completion at the
  center, the core contracts again, heats again,
  and so on
• Once inner core turns to Iron, fires cease in the
  core, internal outward pressure dwindles and
  hydrostatic equilibrium is destroyed. Gravity
  takes over and..

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BanG !!!!!

• The star implodes! (falls in on itself!)
• Core temperature rises again, all heavy elements
  in core undergo Photodisintegration, undoing the
  fusion process of the previous 10 million years.
  End up with electrons, protons, neutrons, and
  photons in core.
• Core compresses, stops and rebounds with a
  vengeance!
• During this rebound, a shock wave sweeps through
  the star blasting all the overlying layers,
  including the heavy elements just formed outside
  the iron core into space a Type 2 Supernova has
  occurred.
• The brightness of a supernova may rival the
  brightness of the entire galaxy in which it
  resides. This period is short few days, maybe
  a month.

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Big and little bangs

• Novae and supernovae are two different types of
  beasts.
• A nova is an increase in the brightness of an
  accreting white dwarf star that is undergoing a
  surface explosion.
• The temporary and rapid change in luminosity can
  occur over a period of a few days.
• On the average, 2 or 3 novae are observed every
  year.
• As to type 1 supernovae, a star has to have a
  buddy for this to occur.

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Type 1 supernovae and white dwarfs

• When an accreting white dwarf exceeds a maximum
  value of 1.4 solar masses (Chandresekhar mass),
  electrons inside cannot provide the pressure
  needed to support the star.
• Star begins to collapse, temperature rises to the
  point where carbon fusion takes place.
• Fusion taking place everywhere throughout the
  star causes it to explode Type 1 supernova
  (carbon-detonation supernova).
• Star is believed to be blasted to bits

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Type 2 supernova remnant

• Crab nebula
• A supernova remnant.
• 1st seen in 1054 A.D.
• 1800 pc from Earth.
• About 2 pc wide
• Has a neutron star, pulsar..
• Speaking of which gt

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Large mass star endings (chapter 22)

• What remains after a supernova (type 2)
  explosion?
• More than what you get from a type 1 explosion,
  thats for sure!

1. Neutron stars 2. Black holes
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Creatures of the deep

• Neutron stars
• A ball (size that of a large city 20 km) of
  neutrons left after a supernova explosion.
• Density 1017 1018 kg/m3 , weight thimbleful
  of neutron star material would weigh 100 million
  tons.
• Gravity extremely powerful youd weigh a lot
  more on this star!
• Carry strong magnetic fields.
• Spin very fast! (a consequence of the
  conservation of angular momentum)

• Black Holes
• Chandrasekhar limit for a neutron star 3 solar
  masses. Above this limit the star cannot support
  itself against its own gravity collapse.
• General Relativity says that this collapse
  punches a hole in space-time called a
  singularity.
• This singularity is surrounded by a an event
  horizon, which defines the absolute edge outside
  of which a photon of light can escape.

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Lets look at neutron stars first

• If youre a neutron star you can decide to
  announce your presence by becoming a Pulsar

Crab pulsar Hubble telescope
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Pulsar emission

• Extremely rapid rotation and combination of a
  strong magnetic field dictates signal properties
  seen by us.
• We see the pulses when they sweep across the Earth

Discovered by Jocelyn Bell, a grad. Student at
Cambridge University, In 1967. Her thesis advisor
won the Nobel Prize for it in 1974.
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Black holes and the speed of light

• Special relativity says that the limiting speed
  in the universe is the speed of light.

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Black holes and curved space-time

• General relativity says that any mass creates a
  dent or depression in space-time.
• The bigger the mass, the greater the depression

Proof
Page 584 figure 22.15
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proof
Deflection of starlight measured in 1919,
confirmed the general theory.
Planetary orbits deviate from Keplers ellipses,
they actually precess
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So.. What happens around a Black Hole?

• Gravitational red shift.
• Light energy is drained near the event horizon.
• No escape of light/radiation upon entering event
  horizon.
• Getting close to event horizon, causes
  spagetification, when youre stretched out long
  ways.