STELLAR EVOLUTION

1
STELLAR EVOLUTION

• The life cycle of stars.

2
EMPTY SPACE?

• So called empty space actually has a density of
  .1 to 1 particles per cubic centimeter.
• Also present are quantum virtual particle pairs
  and all sorts of energetic disturbances such as
  supernova shock waves, gravity waves, and
  radiation.

3
GIANT MOLECULAR CLOUD

• Gravity sometimes accretes material to increase
  the density of space.
• Giant molecular clouds have densities ranging
  from 10 to one million particles per cubic
  centimeter.

4
GRAVITATIONAL COLLAPSE

• Mechanism of gravitational collapse is unknown
  but might be caused by shock waves.
• The GMC collapses and fragments to form Bok
  Globules (star forming cocoons).

5
PROTOSTAR FORMATION

• The loss of gravitational potential energy causes
  heating.
• Protostars fall into three categories depending
  on their mass.
• Small protostars less than .1 solar mass (SM).
• Medium protostars 1-50 SM.
• Massive protostars gt50 SM.

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PROTOSTAR
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FAILED STARS

• Less than .1 SM does not have enough mass to
  produce fusion.
• These Brown Dwarfs are very numerous and may
  account for some of the dark matter theorized
  by cosmologists.

8
FUSION BEGINS

• Protostars with masses of gt.6 SM undergo
  gravitational collapse.
• Heat and pressure increase until hydrogen fusion
  begins.
• The birth of the star blows away dust and gas
  from the cocoon.
• These new stars become Main sequence stars.

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A STAR NURSERY
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MAIN SEQUENCE STARS

• Burn hydrogen in their cores.
• They establish hydrostatic equilibrium.
• Outward pressure from fusion and the Coulomb
  force inward force due to gravity.

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SMALL MAIN SEQUENCE STAR

• Mass is .5 SM or less.
• Live for hundreds of billions of years.
• Usually called COOL RED DWARF STARS.

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MID SIZED STARS

• Mass is .6 5.4 SM.
• Live for approximately 10 billion years.
• Our sun is a mid sized main sequence star.

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GIANT STARS

• Live for only a few million years.
• They are between 10-20 SM.
• They burn their hydrogen very rapidly to maintain
  hydrostatic equilibrium.

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GOING OFF MAIN SEQUENCE

• After all of the hydrogen fuses, the star
  undergoes main sequence turnoff.
• The hydrostatic pressure decreases and the star
  begins collapse.
• Wolf Rayet type stars.

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GERIATRIC LOW MASS STARS

• Stars less than .5 SM.
• Too small to fuse helium.
• Fade and evaporate to form Brown Dwarf Stars.

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MEDIUM STAR

• Stars less than 3.4 SM.
• Helium fuses to form carbon.
• Luminosity and core temperature increase.
• Surrounding gas bloats out to form a Red Giant.

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RED GIANT DEMISE

• Large energy pulsations eject most of the solar
  material.
• This material may recycle to form new stars.
• The star shrinks to form a White Dwarf.

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BINARY SYSTEM WHITE DWARF

• A white dwarf in a binary system can accrete
  material from its partner star to build up mass
  again.
• Little hydrostatic pressure causes rapid collapse
  and a Type 1A supernova.

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GIANT OR SUPER GIANT STAR

• Stars of gt 3.5 SM.
• Huge gravitational pressure collapses the core.
• Temperatures increases and fusion continues until
  Iron is formed.
• Iron can not undergo fusion and the hydrostatic
  pressure drops.

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CORE COLLAPSE

• Rapid end of fusion causes very fast core
  collapse.
• The collapse happens in a fraction of a second.
• This causes a Type 2 supernova.

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NEUTRINO SHOCK WAVES

• The supernova causes shock waves of neutrinos.
• Most of the stellar material is blasted out into
  space.
• The escaping material is bombarded with
  neutrinos.
• The neutrinos are captured and elements heavier
  than iron are formed.

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SMALL STARS

• Stars lt 1.5 SM.
• Gravity collapses them until electron degeneracy
  stops collapse.
• White dwarf forms.
• Evaporates to form a Black Dwarf.

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MID SIZED STARS

• Mass is gt 1.4 and lt 3 SM.
• The collapse forces the electrons into the
  nucleus where they combine with protons to form
  neutrons.
• Neutron or quark stars are formed.

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MASSIVE STARS

• Mass gt 3 SM.
• Gravity overcomes neutron degeneracy and
  collapses the core to form a Singularity.
• A black hole results.