In the beginning

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In the beginning

• Trevor Ireland

GEOL 3022 Planetary Geology 1
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Cosmology

• Largely static view of the universe
• Distances ( time) are big
• Evolutionary time scales of stars are long
• In the beginning(say 13.5 Gyr ago)

"In the beginning the Universe was created. This
has made a lot of people very angry and been
widely regarded as a bad move." Douglas Adams
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pop
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Big Bang

• Singularity
• No passage pre BB
• No time or space
• All matter formed out of bubble of energy
• Transdimensional (?)
• Within 100 Myr, stars and galaxies
• 100 billion stars in 100 billion galaxies

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Big Bang

• Why ?
• need to start somewhere, or do we?
• static models (e.g Fred Hoyle)
• Things are the way they are because they were
  the way they were.

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Microwave background
Predicted by George Gamow Discovered by Arno
Penzias and Robert Wilson, 1965
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COBE
Cosmic Background Explorer
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Ringing in the ears

• 3 K background
• homogeneous to ppm level
• 600 km/s dipole
• small heterogeneities due to knots in the
  expanding bubble
• not consistent with Big Bang ?

http//www.astro.ubc.ca/people/scott/cmb_intro.htm
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Highlights of the Std Model

• 10-43 s Quarks and Bosons become interchangeable
  Gravity force separates
• 10-35 s Electroweak and strong forces separate
• 10-10 s Weak and electromagnetic forces separate
  (limit of physics today)
• 10-3 s Particles form from quarks
• 3 mins Hydrogen and Helium nuclei form

For every one billion particles of antimatter
there were one billion and one particles of
matter.
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Big Bang
Z

• Results
• H 77
• He 23 (roughly)
• Small amounts of D, T, 3He, (Li, Be, B)
• Neutron-addition mass barriers
• No mass 5 or 8
• Freeze out from BB stalls at low mass
• First stars have no metals

(Alpher, Bethe, and Gamow, 1948)
N
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Periodic Tables
cosmochemical
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Nucleosynthesis

• All heavy elements (Z6) formed in stars
• Nuclear reactions
• B2FH, Cameron (in the 50s)
• Apart from secondary effects of minor importance,
  the transmutation of elements is the entire cause
  of the presence of all elements in stars they
  are all being synthesized continually in the
  stars which are assumed to have started as pure
  masses of hydrogen further, transmutations are
  the only source of nuclear energy (S.
  Chandrasekhar).

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Cosmic Abundances

• Isotopic and Elemental abundances suggest several
  processes responsible
• Nuclear reactions

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Stars

• Essentially defined by mass
• Composition relates only to metal abundances
  (lt2)
• H burns to He
• 41H ? 4He (E)
• Mp 1.0078, MHe 4.0026
• ?M 4.0312 - 4.0026 0.0286 amu
• E mc2 0.02861.66e-279e16
• 4e-12 J 26 MeV (c.f. thermal electron 0.02 eV)

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Stars

• Hertzsprung Russell Diagram
• Colour - brightness
• Stellar emission relates to nuclear reactions

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The first generation

• Stars composed of H He
• Low metallicity Pop III stars (huge!)
• Energy considerations
• how do we ignite a star?
• gravitational collapse (lot of energy)
• Gets particles closer together
• H, He nuclei

RSAA Astronomers have found a star that may have
been one of the very first to form in our Milky
Way galaxy. The star, HE0107-5240, is 80 as
massive as the Sun, but has practically no metals
in it, less than 1/200,000th the amount found in
the Sun. This makes it the most metal-weak star
ever found, an indication of extreme age. Younger
stars have more metals in their makeup because
they form in regions that have been enriched by
the chemicals produced by earlier generations of
stars. (Oct 31, 2002)
Pop I normal metal (1) Pop II metal-poor (10-2
solar Pop III ultra-poor (10-5 solar)
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Lighting up

• Two particle reactions
• p p -gt 2He (unstable) -gt p p
• p 4He -gt 5Li (unstable) -gt p 4He
• 4He 4He -gt 8Be (unstable) -gt 4He 4HeNo
  major two-particle exothermic reactions!
• H D -gt 3He gis exothermic but not much D
  around
• So, how does a star start?

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PP reactions

• Weak nuclear reaction (Bethe, 1939)
• p-gt n e n
• Mn gt Mp (endothermic - needs E)
• but, consider n(p,n)D
• binding energy of D makes reaction exothermic
• p p -gt D e n (0.42 MeV)
• e e- -gt g (1.022 MeV)
• Net 1.44 MeV

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10 billion years

• A tight balance
• 4H ? 4He (?M of 7) Goldilocks!
• 6 would not sustain
• 8 would burn out too quickly
• gravitational contraction vs stellar outflow
• neutrino emission n-gt p e- n is instant
  freeze
• collapse until ignition then steady state
• Were half way through our 10 Gyr
• outflow pressure gravitational collapse

A 0.8M star remains on the main sequence for an
age greater than the age of the Universe
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When the fuel runs out...

• Star can no longer withstand gravitational
  collapse
• Contraction higher pressure, energies
• If large enough, He burning starts
• Already seen 4He 4He -gt 8Be (unstable)

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Triple a reaction

• Two particle reactions can not proceed
• 4He4He ? 8Be (t½3x10-16s) ? 4He4He
• but its stable for long enough!
• 8Be 4He -gt 12C g and away we go...
• 12C(a,g)16O
• 16O(a,g)20Ne etc
• Stellar onion rings
• Note na peaks in abundance curve

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Another squeeze

• After He burning cannot support star, contraction
  to light heavier nuclei
• C burning, O burning -gt Mg,Si
• Si burning -gt Fe group
• Fe abundance peak has highest binding energy per
  nucleon, so no more fusion
• Star must be massive enough to ignite the
  reactions or it will die out (commonly as a white
  dwarf of 12C and 16O lt 8 solar masses).

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The first ashes

• Ashes of first generations stars act as catalysts
  in later stars
• e.g. CNO cycle for H burning
• 12C (p,g) 13N -gt 13C e n
• 13C (p,g) 14N
• 14N (p,g) 15O -gt 15N e n
• 15N (p,a) 12C

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Planetary Nebulae
Thermally Pulsing Assymptotic Giant
Branch (TP-AGB)
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The End for most
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Chart of the Nuclides