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Announcements
• Next time: finish reading The Five Ages.
• Exam 1 is scheduled for next Wednesday. Will cover Five Ages of the Universe only.
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Colored Card QuestionThe Stelliferous Era begins in which cosmological decade?a) The 14th
b)The 25th
c) The 6th
d)The 10th
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Another Colored Card Question
During the Degenerate Era, most of the unburned hydrogen can be founda) in cool white dwarfsb) as cool gas between the galaxiesc) in giant molecular clouds in the galaxiesd) in brown dwarfs
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One More Colored Card Question
The Black Hole Era begins in which cosmological decade?a) The 40th
b) The 10th
c) The 75th d) The 25th
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The Stelliferous Era
The first generation stars may have been mostly dark matter: Dark Stars
These stars may have had several thousand solar masses
6<h<14
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CMB shows seeds of first galaxies
The variation in temperature is only ~ one part in 105. That’s enough to give rise to structure.
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First galaxies were small irregular galaxies which slowly became spirals
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Which came first: the black hole at the center of the galaxy or the galaxy?
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Stellar formation today takes place in giant clouds of gas & dust
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The gestation period depends on the mass
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The fate of a star depends almost entirely on its mass
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Death by planetary nebula formation
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Death by supernova
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Death by Hypernova
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The current population of stars
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Eventually only low mass stars are left
The smallest red dwarf stars may live for tens of trillions of years but eventually even they die.
At the end of the stelliferous era only supermassive black holes and stellar corpses are left.
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The Degenerate EraWhite Dwarfs and planets
Black Holes
Brown Dwarfs
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The degenerates all start off as
stars
White dwarf’s, neutron stars and stellar mass black holes all start as stars. There are larger black holes, galactic black holes, that didn’t start as stars, though.
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Brown Dwarf Stars are failed stars
They are not entirely degenerate. These, planets and any surviving asteroids or comets are the sole reservoirs of ordinary matter left during the degenerate era.
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There are currently many more stars than brown dwarfs
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Brown Dwarfs are comparable in size to Jupiter
The interiors of brown dwarf’s become highly compressed so they don’t get much larger than Jupiter even with 40 or 50 times the mass. They can become degenerate at their core
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White Dwarfs are the size of planets with the mass of stars
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Some White Dwarfs “grow” by accreting mass from companions
During the Degenerate Era this doesn’t happen any more but it is not uncommon during the Stelliferous Era
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In degenerate matter only the highest energy levels are available
Single atom Energy Level Diagram
Degenerate Matter Energy Level Diagram
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Degenerate objects get smaller when mass is added
This applies to white dwarf’s and neutron stars but not black holes. Black holes are beyond degenerate
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During the Degenerate Era most of the energy may come from dark matter annihilation
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Neutron Stars aren’t entirely neutrons
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Eventually the protons decay
There are other possible decay mechanisms. The current best estimate for the half-life of the proton is ~1034 years. Once all the protons decay away, there is no ordinary matter, degenerate or non-degenerate, left in the universe
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At the end of the Degenerate Era only black holes are left