Explorations of the Universe

1
Explorations of the Universe

• Lives of the Stars

2
Two Profound Ideas

• The Sun is a Star
• We Are Made of Starstuff

3
Large Numbers

• 10 x 10 x 10 x 10 104
• 10 x 10 x (n times) 10n
• To multiply, add exponents
• 10,000 x 100,000 1,000,000,000
• 104 x 105 1045 109

4
More About Large Numbers

• 1,000,000,000/10,000 100,000
• 109/104 105 109-4
• To divide, subtract exponents
• 1000/100 103/102 103-2 101 10
• Anything to the first power equals itself

5
A Paradox of Scientific Notation

• Not really a paradox, but hard for many people to
  accept
• 100/100 102/102 102-2 100 1
• Anything to the zero power equals 1

6
Negative Exponents

• 1000/100,000 103/105 103-5 10-2 1/100
  .01
• 10n x 10-n 10n-n 100 1
• 10-n 1/10n

7
Does Anybody Need Really Big Numbers?

• 10100 googol
• 1010100 10googol googolplex
• Statistical Physics energy distribution of air
  molecules in a room
• Need to know total possible energy states
• Roughly 10number of molecules 101026
• Not a googolplex, but still pretty huge

8
Infinity

• The symbol for infinity is not a number - you
  cant calculate with it.
• The mathematician Georg Cantor studied
  transfinite numbers, denoted by the Hebrew letter
  Aleph

9
Forces in Nature

• Long Range
• Gravity
• Electromagnetism
• Short Range - Only Within Atoms
• Weak Nuclear
• Strong Nuclear
• Other???

10
Atoms

• Democritus 400 B.C.
• Lucretius 1st c. B.C.
• Medieval new elements
• Definition of Element
• Ratios in Chemical Reactions
• Crystallography

11
Atoms

• Nucleus Almost all Mass in Atom
• Protons Determines Element Identity
• Neutrons
• Protons repel (electromagnetism) but strong
  nuclear force is stronger, holds it together
• Too many protons unstable (radioactive)
• Electrons
• The part that engages in chemical reactions

12
Why Alchemy Didnt Work

• Atomic energies are measured in units called
  electron volts (ev - very tiny)
• Energy binding electrons to an atom are a few ev
• Energies binding particles in the nucleus are
  millions of ev
• Trying to alter elements by chemical means is
  like trying to crack a safe with a feather

13
The Heavens Are Not Changeless

• The Stars Move
• Most of our constellations would have been
  unrecognizable to Neanderthal Man
• The Solar System Moves
• Very few of our nearby stars would have been
  visible to the first humans
• Stars are Born, Live and Die
• Many of our brightest stars did not exist in the
  days of the dinosaurs

14
Low-mass stars

• Stars below 8 solar masses turn into red giant
  stars.

15
Low-mass stars

• Collapse leads to a rise in core temperature.

16
Life cycle

• Interiors of low-mass stars.

17
Losing mass

• The outer layers are lost as a planetary nebula.

18
Losing mass

• Asymmetric mass loss can be seen in the range of
  planetary nebulae.

19
White dwarfs

• White dwarfs are the hot carbon/oxygen core of
  low-mass stars.

20
The Chandrasekhar limit

• The maximum mass of the degenerate core of the
  white dwarf that can be supported by electron
  degeneracy.

21
Inside stellar remnants
22
High-mass stars

• Over 8 solar masses, stars can reach interior
  temperatures high enough for carbon to fuse.

23
High-mass fusion

• Higher mass stars burn heavier elements.

O-1
O-1
O-1
24
The inert iron core

• High-mass stars have shells of heavier and
  heavier elements.

25
Countdown to supernova
26
A recent supernova

• Supernova 1987A was observed from start to finish.

27
Neutron stars pulsars

• A neutron star is even more dense than a white
  dwarf.

28
Neutron stars
29
Summary of stellar death
30
The end of a massive star

• What happens when a dying stellar core is above
  three solar masses?

31
The structure of a black hole

• Mass has reached infinite density and winked out
  of spacetime

32
Black holes

• Any matter that crosses the event horizon winks
  out of the universe.