1. accretion disk -

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1. accretion disk -

• flat disk of matter spiraling down onto the
  surface of a star. Often from a companion star.

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2. alpha process -

• Two step process in the center of stars which
  have silicon-28 in their cores.
• Photodisintergration breaks nuclei into helium
  nuclei (alpha particles) which then combine into
  heavier elements.

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3. carbon detonation supernova -

• a type-I supernova.
• White dwarf in a binary system accretes enough
  mass that electron degeneracy pressure can no
  longer support the star.
• The star collapses and the temperatures reach a
  level that causes carbon fusion in all parts of
  the star simultaneously and an explosion results.

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4. Chandrasekhar mass -

• Maximum mass of a white dwarf if electron
  degeneracy pressure is to prevent gravitational
  collapse.
• Once it is exceeded a type-I supernova results.

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5. helium capture -

• The formation of heavier elements by the capture
  of a helium nucleus.
• This requires less energy than the combining of
  like nuclei so it happens more readily.

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6. neutron degeneracy pressure -

• Pressure that results when neutrons are pushed
  together to the point of contact.
• The neutrons resist being compressed.

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7. neutronization -

• When the collapsing core of a high mass star is
  compressed to the point that protons and
  electrons are crushed together to form neutrons
  and neutrinos.
• This is one of the major occurrences in the
  formation of a type-II supernova.

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8. nova -

• A star that suddenly increases in brightness,
  then slowly fades back to its original
  luminosity.
• The result of an explosion on the surface of a
  white dwarf, cause by the accumulation of matter
  from a binary companion.

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9. photodisintegration -

• Photons at high temperature breaking heavy
  elements into lighter nuclei, and eventually to
  protons and neutrons.
• Prior to a supernova, photodisintegration
  undoes all the previous 10 billion years of
  nuclear fusion.

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10. progenitor -

• A star that generates a supernova explosion.

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11. recurrent nova -

• A star that goes nova a number of times over
  the course of several decades.

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12. r-process -

• Creation of heavy elements by neutron capture
  during supernova explosions.
• Free neutrons streaming from an exploding
  supernova collide with heavy elements and produce
  heavier elements. The heaviest elements in the
  universe are produced by the r-process.

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13. s-process -

• Neutrons captured by nuclei in a star until an
  unstable isotope is created.
• The nucleus then decays to a new stable nucleus
  this continues until no heavier stable nuclei
  exist.
• The s means slow the time between captures
  is long compared to the half-lives of the
  radioactive elements produced.

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14. standard candle -

• Any object with a recognizable appearance and a
  known luminosity such that it can be used to
  establish distance.
• Supernovae are good standard candles.

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15. stellar nucleosynthesis -

• Formation of heavy elements by the fusion of
  lighter nuclei in the cores of stars.
• All elements except for H and He are formed by
  stellar nucleoynthesis.

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16. supernova -

• Explosive death of a star, caused by sudden
  nuclear burning (type-I), or enormously energetic
  shock waves (type-II).

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17. supernova remnant -

• Scattered glowing remains from a supernova that
  occurred in the past.
• Crab Nebula is one example.

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18. type-I supernova -

• A carbon detonation supernova.
• (see 3).

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19. type-II supernova

• Highly evolved stellar core rapidly implodes and
  then explodes, destroying the surrounding star.

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1. What makes a nova?

• A white dwarf in a binary system collects
  material from its companion. This collected gas
  gets hotter and denser until the hydrogen ignites
  and produces helium in an intense surface burn.

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2. What makes a light curve?

• The magnitude of the nova or supernova changes
  over time a graph of this change is called a
  light curve.

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3. What is a supernova?

• A massive stellar explosion which destroys the
  original star.

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4. How often can we expect to see a supernova?

• We should expect to see a supernova in a visible
  part of our galaxy every 100 years or so.
• We are long overdue (since 1604).

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5. What evidence is there that many supernova
have occurred?

• We can detect the glowing supernova remnants.

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6. According to historical accounts, how did the
explosion creating the Crab Nebula appear to
observers on Earth?

• Its brightness exceeded that of Venus.
• Perhaps was brighter than the Moon.
• Could be seen in the daytime for a month.

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7. How do supernovae work as standard candles?

• We know the absolute brightness of all supernovae
  is the same, so we can compare this to the
  apparent brightness and find the distance.

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8. Which elements existed in the early universe?

• hydrogen and helium

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9. How were all of the other elements in the
universe formed?

• They were formed by stellar nucleosynthesis
  formed by nuclear fusion in the core of stars.

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10. Why do stars cores evolve into iron, but not
into larger elements?

• Nuclear fusion involving iron does not produce
  energy. Iron nuclei are so compact that energy
  cannot be removed by combining them into heavier
  elements. This loss of energy causes a loss of
  pressure which stops fusion (temporarily).
• Iron formation is a fire extinguisher.

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11. How are nuclei heavier than iron formed?

• 1. The s-process (slow). Iron captures a
  single neutron, and then another, and then
  another. Eventually an unstable form of iron is
  formed, and it decays into a heavier stable
  element.

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• 2. The r-process(rapid). The intense pressures
  involved in a supernova explosion force heavier
  elements to gain free neutrons produced by the
  explosion. This occurs too rapidly for the nuclei
  to decay and therefore produce elements that
  cannot be formed by the s-process.

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12. What makes a massive star collapse?

• Gravitational pull that exceeds the heat and
  pressure that holds a star at its present volume.
• The heat decreases with the fusing of iron whish
  results in a decrease of pressure.