Supernova Remnant Cas A, 17-18 light years in diameter

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50-500 million K Gas
10 thousand K gas
White Dwarf
Neutron star
Supernova Remnant Cas A, 17-18 light years in
diameter
Planetary Nebula Ring Nebula, 1/3 light year
diameter
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Type II Supernova
Core burns all fuel, from hydrogen all the way to
iron then the star collapses!
Only Massive (10 solar masses) or more will do
in much less than the age of the universe
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But havent been able to use type IIs, yet! Too
hard to calibrate

• Instead we use Type Ia

• Type Ia come from binary star systems that have
  one member that is a white dwarf (WD).
• The WD is less than 1.4 solar masses
• Explodes if it goes over (one jelly donut too
  many)

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• A WD is a star core
• From a low mass (4 solar masses, about)
• Envelope was blown off
• Left with core of less than 1.4 solar masses,
• NO nuclear burning
• It sits there and cools off (unless it eats
  one jelly donut too much)

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• The limit of 1.4 solar masses and is derived from
  basic physics

• The limit has name Chandrasekhar limit

• When accreted mass on white dwarf pushes the WD
  over the 1.4 solar mass limitgt

• Pow!

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• Exceeding limit tends to lead to more uniform in
  brightness explosions
• And what isnt the same (some are slower than
  others), weve been able to calibrate
• Need to get extra mass onto WD gt
• Binary system

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Mass Transfer!
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Bottom line WL is non-zero!
Are there any ways out?
Yes!
Either SNeIa are different in past
Or grey dust or ??
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What are some of the problems

• Distant objects might not be same as same as
  nearby ones gt
• Standard candles arent so standard

• Intervening material which increases with D
  might also matter.

• Distant faint hard to see

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Can distant SNeIa be different from nearby ones?

• Yes, because the material that makes up stars
  depends on when the star formed gt

• Stellar Evolution, part two

• stars explode, dump their material back to
  interstellar medium enriched with metals
  (anything heavier than helium)

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• Metals are not made in BB!
• The very first stars in galaxies should be just H
  and He.