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

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

But haven’t 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)

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)”

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 limit=> Pow!

Exceeding limit tends to lead to more uniform in brightness explosions And what isn’t the same (some are slower than others), we’ve been able to calibrate Need to get extra mass onto WD => Binary system

Mass Transfer!

Bottom line: WL is non-zero! Are there any ways out? Yes! Either SNeIa are different in past Or “grey dust” or ??

What are some of the problems Distant objects might not be same as same as nearby ones => Standard candles aren’t so standard Intervening material which increases with D might also matter. Distant = faint = hard to “see”

Can distant SNeIa be different from nearby ones? Yes, because the material that makes up stars depends on when the star formed => Stellar Evolution, part two: stars explode, dump their material back to interstellar medium enriched with “metals” (anything heavier than helium)

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