Announcements

• Next time: finish reading The Five Ages.

• Exam 1 is scheduled for next Wednesday. Will cover Five Ages of the Universe only.

Colored Card QuestionThe Stelliferous Era begins in which cosmological decade?a) The 14th

b)The 25th

c) The 6th

d)The 10th

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

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

The Stelliferous Era

The first generation stars may have been mostly dark matter: Dark Stars

These stars may have had several thousand solar masses

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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.

First galaxies were small irregular galaxies which slowly became spirals

Which came first: the black hole at the center of the galaxy or the galaxy?

Stellar formation today takes place in giant clouds of gas & dust

The gestation period depends on the mass

The fate of a star depends almost entirely on its mass

Death by planetary nebula formation

Death by supernova

Death by Hypernova

The current population of stars

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.

The Degenerate EraWhite Dwarfs and planets

Black Holes

Brown Dwarfs

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.

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.

There are currently many more stars than brown dwarfs

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

White Dwarfs are the size of planets with the mass of stars

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

In degenerate matter only the highest energy levels are available

Single atom Energy Level Diagram

Degenerate Matter Energy Level Diagram

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

During the Degenerate Era most of the energy may come from dark matter annihilation

Neutron Stars aren’t entirely neutrons

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

At the end of the Degenerate Era only black holes are left