Explorations of the Universe Lives of the Stars

Two Profound Ideas The Sun is a Star The Sun is a Star We Are Made of Starstuff We Are Made of Starstuff

Large Numbers 10 x 10 x 10 x 10 = x 10 x 10 x 10 = x 10 x … (n times) = 10 n 10 x 10 x … (n times) = 10 n To multiply, add exponents To multiply, add exponents –10,000 x 100,000 = 1,000,000,000 –10 4 x 10 5 = = 10 9

More About Large Numbers 1,000,000,000/10,000 = 100,000 1,000,000,000/10,000 = 100, /10 4 = 10 5 = /10 4 = 10 5 = To divide, subtract exponents To divide, subtract exponents 1000/100 = 10 3 /10 2 = = 10 1 = /100 = 10 3 /10 2 = = 10 1 = 10 Anything to the first power equals itself Anything to the first power equals itself

A “Paradox” of Scientific Notation Not really a paradox, but hard for many people to accept Not really a paradox, but hard for many people to accept 100/100 = 10 2 /10 2 = = 10 0 = 1 100/100 = 10 2 /10 2 = = 10 0 = 1 Anything to the zero power equals 1 Anything to the zero power equals 1

Negative Exponents 1000/100,000 = 10 3 /10 5 = = = 1/100 = /100,000 = 10 3 /10 5 = = = 1/100 = n x 10 -n = 10 n-n = 10 0 = 1 10 n x 10 -n = 10 n-n = 10 0 = n = 1/10 n 10 -n = 1/10 n

Does Anybody Need Really Big Numbers? = “googol” = “googol” = 10 googol = googolplex = 10 googol = googolplex Statistical Physics: energy distribution of air molecules in a room Statistical Physics: energy distribution of air molecules in a room –Need to know total possible energy states –Roughly 10 number of molecules = –Not a googolplex, but still pretty huge

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

Forces in Nature Long Range Long Range –Gravity –Electromagnetism Short Range - Only Within Atoms Short Range - Only Within Atoms –Weak Nuclear –Strong Nuclear Other??? Other???

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

Atoms Nucleus: Almost all Mass in Atom 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 Electrons –The part that engages in chemical reactions

Why Alchemy Didn’t Work Atomic energies are measured in units called electron volts (ev - very tiny) Atomic energies are measured in units called electron volts (ev - very tiny) Energy binding electrons to an atom are a few ev Energy binding electrons to an atom are a few ev Energies binding particles in the nucleus are millions of 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 Trying to alter elements by chemical means is like trying to crack a safe with a feather

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

Low-mass stars Stars below 8 solar masses turn into red giant stars. Stars below 8 solar masses turn into red giant stars.

Low-mass stars Collapse leads to a rise in core temperature. Collapse leads to a rise in core temperature.

Life cycle Interiors of low-mass stars. Interiors of low-mass stars.

Losing mass The outer layers are lost as a planetary nebula. The outer layers are lost as a planetary nebula.

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

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

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

Inside stellar remnants

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

High-mass fusion Higher mass stars burn heavier elements. Higher mass stars burn heavier elements. O -1

The inert iron core High-mass stars have shells of heavier and heavier elements. High-mass stars have shells of heavier and heavier elements.

Countdown to supernova

A recent supernova Supernova 1987A was observed from start to finish. Supernova 1987A was observed from start to finish.

Neutron stars & pulsars A neutron star is even more dense than a white dwarf. A neutron star is even more dense than a white dwarf.

Neutron stars

Summary of stellar death

The end of a massive star What happens when a dying stellar core is above three solar masses? What happens when a dying stellar core is above three solar masses?

The structure of a black hole Mass has reached infinite density and winked out of spacetime Mass has reached infinite density and winked out of spacetime

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