Stars Part Two: - tuhsphysics.ttsd.k12.or.us

Stars Part Two: - tuhsphysics.ttsd.k12.or.us

Stars Part Two: Stellar Evolution Overview of the life of a star: 1. Formation of protostar 2. Main sequence star

3. Red giant White dwarf or Supernova Neutron star or Black hole Formation of protostar:

1. Gaseous clouds contract under their own gravity. 2. Gravitational potential turns to heat. 3. Heat and pressure start fusion.

Birth of a star IP Demo: Star_Birth.ip Birth of a star 1. Rotation speeds up (demo) 2. Mechanism for slowing

3. B-Field Polar Jets Birth of a star 1. Spin Slows - Fusion 2. Nebula often blown away 3. Accretion disk

Birth of a solar system: Accretion Disk Icy and Gassy Stuff

Rocky Stuff The New Star The Solar System National Geographic Magazine

The Inner Planets:: Mercury Venus Earth

Mars Close together (Relatively) Terrestrial (made of rock like Earth) Asteroids

The Outer Planets:: Jupiter Saturn

Uranus Spread out (Relatively) Gas giants Neptune

Pluto Life on the Main Sequence: 1. Energy comes primarily from the Proton-Proton cycle:

1 H + 1H = 2H + e+ + 1 H + 2H = 3He + 3 He + 3He = 4He + 1H + 1H

(requires heat and pressure) Thermal Agitation balances the tendency of gravity to crush a star: Gravity Crushing Pressure

Heat Thermal Agitation 1. The rate of burn depends roughly on the cube of the mass

L mn where 3 < n < 4 2. Large stars Brief 3. Small stars Durable 4. Big stars are Brief, Bright, and Blue 5. Diminutive stars are Durable, Dim and reD

.01 Billion Years 1 Billion Years .1 Billion Years 100 Billion

Years 10 Billion Years 500 Billion Years From Robert Garfinkles Star Hopping From Jay Pasachoffs Contemporary Astronomy

A Star trying to be too big From Jay Pasachoffs Contemporary Astronomy He accumulates in the core of the star:

4 The death of a star: 1. 2.

3. 4. 5. 6. 7. 8.

9. Helium displaces Hydrogen in core Star Cools Heat energy no longer balances gravity. Gravity collapses the He core.

Implosion spurs hydrogen fusion Star is puffed up It is now a Red Giant Sun expands orbit of Venus or Earth Star 8 solar masses -> 1 or 2 residual

Collapse of the He Core: Expands Cools Down Helium Fusion:

1. He Fusion 4 He + 4He = 8Be + 4 He + 8Be = 12C + 2. Also:

4 He + 12C = 16O + (mainly) 4 He + 16O = 20Ne + 4 He + 20Ne = 24Mg +

3. Heats and contracts: Helium Fusion: Heats up and contracts Carbon Fusion: (dj vu?)

1. 2. 3. 4. 5.

Carbon displaces He in Core Heat energy no longer balances gravity. Gravity collapses the Carbon core. Implosion spurs He fusion The outer layer of the star expands, and cools briefly:

Collapse of the Carbon Core: Cools and Expands again Carbon Fusion: 1. IFF m > .7 Msun:

12 C + 12C = 24Mg + 16 O + 16O = 28Si + 4He 2. Nuclei as heavy as 56Fe and 56Ni can be created if the star core is hot enough.

3. Nucleosynthesis and fusion stop with 56Fe and 56Ni (Binding energy) Most tightly bound nuclei (If you go from less to more bound you release

energy) Fe and 56Ni 56

From Douglas Giancolis Physics So far: Collapse of C core

Carbon Fusion (if > .7 Msun) Degenerate Matter

Helium Fusion Collapse of He Core Hydrogen Fusion stops

How do we know all this? By observing Globular clusters Planetary Nebulas: 1.

2. 3. 4. 5. Some white dwarves with mass 1-7xMsun

Shrinks spins fast Polar jets Material ejected by previous explosions Some are binary If the residual mass of the star is less

than 1.4 times the current mass of the sun, our story ends here. A star with the mass of the sun becomes a White dwarf about the size of the earth. The Pauli exclusion principle prevents

the star from collapsing any further. It gradually runs out of Carbon fuel, getting dimmer and dimmer, until it becomes a black dwarf. If the residual mass of the star is less

than 1.4 times the current mass of the sun, our story ends here. A star with the mass of the sun becomes a White dwarf about the size of the earth. The Pauli exclusion principle prevents

the star from collapsing any further. It gradually runs out of Carbon fuel, getting dimmer and dimmer, until it becomes a black dwarf. Now for something completely

different. Wanna hear a scary story? Do not adjust your television set We are on a special schedule Life After the Main Sequence

Starring: Marcela Supernova Joe Neutron Star Bob Quasar Mary Pulsar Freda Black Hole

Music by Warped Space Time If the mass of the star is greater than 1.4 times the mass of the sun. (This is called the Chandrasekhar limit) it dont care about no Pauli exclusion principle.

When the Carbon Fusion fires burn down, gravity crushes the star. The collapse of the star releases an incredible amount of energy. The star becomes a supernova, increasing in brightness by billions of times for a few

days, and then dies out. The terrific energy released by the collapse of the star creates elements heavier than Iron, and forces electrons and protons to combine creating neutrons.

Dogs become cats. Republicans support campaign finance reform. Democrats vote for tax cuts. In February of 1987, a supernova occurred in the Large Magellenic Cloud, 170,000 ly from Earth. It was briefly visible to the naked eye.

(Assuming your eye was naked in Australia) Neutron Stars: 1. Supernova remnant is composed almost entirely of neutrons. 2. White Dwarfs are the size of planets.

3. Neutron stars are the size of towns. 4. Some Neutron stars spin a thousand times a second. 5. The pressure is so high in the core atomic nuclei cannot exist. 6. The outer envelope is about a mile thick - a

crust of nuclei and electrons. 7. The core is a super-fluid. Picture of a Neutron Star: Ticks are 5 seconds

1. In 1967, Antony Hewish of Cambridge University in England was studying the scintillation of radio sources due to the solar wind. 2. A graduate student named Jocelyn Bell Burnell discovered a strong night time source of

twinkling. 3. Its location was fixed with respect to the stars. From Jay Pasachoffs Contemporary Astronomy Pulsars: 1. Pulsars emit pulses some as short as 1/40th of a

second. 2. There are many things they could not be. 3. The only thing small enough, and rotating fast enough was a neutron star From Jay Pasachoffs Contemporary Astronomy

Pulsars Movies Real photos from hubble Animation Black Holes:

1. If the mass of the neutron star is bigger than about 2 or 3 solar masses, it dont care about no neutron exclusion principle. 2. Gravity collapses the neutron star even further. 3. The star becomes a black hole - an object from which even light cannot escape.

4. Light is really fast. 5. The curvature of space-time becomes infinite. 6. General relativity doesnt work. 7. Um we dont yet have a quantum theory of gravity.

Black Holes: 1. Hawking radiation. 2. Orbit of stars 3. The Andromeda galaxy has stars orbiting a dark object that is 30 to 70 million times the mass of the sun.

Picture of a Black Hole: Quasars: (Quasi-stellar radio source) 1. 2.

3. 4. 5. Massively bright. (10% in-falling mass converted) Intense radio source.

Red shifted radiation. Black holes eating matter. Usually located in the centers of galaxies Quasars: 1.

2. 3. 4. 5. 6.

In falling material forms an accretion disk. Quasars are ravenous beasts. Magnetic fields The accretion disk gets hot. The accretion disk has tornadoes that create jets Predictions

1. Old bright Quasars are rare, young ones common 2. Recently disturbed galaxies should have bright quasars.

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