© 2005 pearson education inc., publishing as addison-wesley the fate of our sun & the origin of...

© 2005 Pearson Education Inc., publishing as Addison-Wesley

The Fate of our Sun&

The Origin of Atoms

• The Death of our Sun and other Stars• Nuclear Reactions creating new atoms• The Big Bang: Origin of H and He

Lecture 23

Notes

• HW due Friday: Read Chapter 14 Mastering Astronomy: Chapt 14

• No HW or Desc. Sections due next week (Thanksgiving)• Next Week: Start Chapter 24: Life in the Universe


The Fate of our Sun&

The Origin of Atoms

• The Death of our Sun and other Stars• The chemical enrichment of our Galaxy• The Big Bang: Origin of H and He

Lecture 23


You can measure the amount of different atoms from darkness of the absorption lines.

Dark spectral lines are caused byabsorption of light by atoms in the Sun’s atmosphere.

Chemical Composition of the Sun

Magnesium Sodium

Calcium Iron


Composition of the Sun(by Mass)

70%28%

0.2%0.3%

C, N, O, Ne, Fe, Others: 2%

Hydrogen

He

Abundances of atoms in the Sun is representative of the universe as a whole:Hydrogen and Helium Dominate.

The 92 atomic elements were constructed by nuclear reactions in the centers of stars - - -

The Origin of the Atomic Elements

All made in stars, except hydrogen, helium and lithium.


Tom Lehrer’sThe Elements

• http://www.youtube.com/watch?v=zGM-wSKFBpo

• http://www.youtube.com/watch?v=zGM-wSKFBpo• Tom Lehrer singing it:

Missing Lawrencium. Listen for• Berkelium and Californium• http://www.youtube.com/watch?v=AcS3NOQnsQM

http://www.youtube.com/watch?v=zGM-wSKFBpo




Nuclear Reactions Fusion of Hydrogen to Helium

Center of the Sun

Temperature = 15 Million K

Collisions between atoms so violent: • electrons removed from atoms: Atoms are Ionized• leaving bare nucleus of each atom.

Computer models (balancing gravity with pressure) show:

Nuclei of atoms collide & react


Nuclear Fusion in the Sun:Proton-Proton Chain

IN: 6 H, (2 e-) OUT: He, 2 H, 2 e, 4

4 H nuclei are converted into 1 He nucleus and energy is released.


Mass Input: 4 p Mass Output: 1 He (2p + 2n)Look up Masses of particles:

Mass Input = 1.007 Mass Output

Mass is missing ! Converted to Energy:

E = mc2

Luminosity of Sun:Nuclear Burning of H to He

Hydrogen is converted to Helium in Sun-like stars.


The Death of the Sunin 5 Billion Years

• Sun’s Core becomes pure helium! • No Hydrogen burning possible.• The Helium core begins to collapse.

– H shell (around Helium) heats up and H fusion begins there.– Outer layers of the Sun expand.– The Sun enters red-giant phase of its life.

Original Sun Expanding:“Giant Star”


Giant Star Phase• The He core collapses until it heats to 108 K

– He fusion begins ( 3 He C) Carbon forms!

• The star, called a Giant, is once again stable.– Gravity balanced by pressure, from He fusion reactions– Giant stars create, and release, most of the Carbon in the

universe: Key ingredient for organic molecules and life.

The Dying Sun: 5 billions years from now


Fusion of 3 helium nuclei into Carbon

“Triple-Alpha “


Planetary Nebula

• When the Giant star exhausts its Helium fuel in the central core:

– the Carbon core collapses.

– Low & solar-mass stars don’t have enough gravitational energy to heat to 6 x 108 K (temperature where Carbon fuses)

• The He & H burning shells produce huge amounts of energy. • The energy blows away the star’s outer layers of gas:• Making a “planetary nebula”.


Planetary Nebulae

Cat’s Eye Nebula

Twin Jet Nebula


Planetary Nebulae

Ring Nebula Hourglass Nebula

The collapsing Carbon core becomes a White Dwarf


When High Mass Stars Die:Supergiants

• They Contract, heat up to 600 million K. – C fuses into O.

They exhaust H fuel.He C .




• C is exhausted, core collapses until O fuses.

• The cycle repeats itself.– O burns to Ne.






• The cycle repeats itself.– O burns to Ne.– Ne burns to Mg.






• The cycle repeats itself.– O burns to Ne.– Ne burns to Mg.– Mg burns to Si.– Si burns to Fe.



Supernova• The mass of the iron (Fe) core increases - Iron can’t burn: - No nuclear reactions: no energy production!

– Gravity overwhelms the gas pressure– Star Collapses!– Electrons are squeezed into protons neutrons

• The neutron core collapses until abruptly stopped by neutrinos flying outward!– this takes only seconds– The core recoils, bounces, and

neutrinos force the gas outward in an explosion.

Core-CollapseSupernova


Supernova

• The mass of the iron (Fe) core increases - Iron can’t burn: - No nuclear reactions: no energy production!

– Gravity overwhelms the gas pressure– Electrons are squeezed into protons neutrons

• The neutron core collapses until abruptly stopped by neutrinos flying outward!– this takes only seconds– The core recoils, bounces, and

neutrinos force the gas outward in an explosion.


Supernova Explosions

Crab Nebula in Taurussupernova exploded in 1054

The explosion brings temperature toBillions of degrees:

The elements heavier than Fe are instantly created

Four supernovae have been observed in our part of the Milky Way Galaxy: 1006, 1054, 1572, & 1604


Supernovae

Veil Nebula Tycho’s Supernova (X-rays)exploded in 1572


Supernova Remains


The atoms that compose your human body were made in

supernova explosions

The 92 atomic elements were all constructed in the centers of stars

(except hydrogen, helium and lithium).


Supernova Explosion: The first 0.15 seconds

Shock wave is created when the core of a massive star collapses to a proto-neutron star. The shock does not immediately explode the star but "stalls" (because the outer parts of the star [not shown in the movie] are exerting ram pressure on it). The shock is "revived" within a tenth of a second from heating by neutrinos emitted from the proto-neutron star. The different colors correspond to gas of different temperature.

Core-Collapse Supernova Explosion


The atoms that compose your human body were made in

supernova explosions





Where did all the Hydrogen and Helium

Come from?





• Explosion: Hot and Dense. Over a trillion degrees.• Universe expands ever since. Accelerating now.• Science can not describe what happened before the Big Bang.

• Time and Space Created.• 13.5 Billion Years Ago.

Depiction of Big Bang


t < 0.001 sec

• Quarks and Electrons as numerous as photons.

(No Protons or neutrons: At billions of degrees,any protons collide, break apart into quarks.)


Quarks and Photons Annihilate:Equilibrium


t < 0.001 sec

• Quarks and Electrons as numerous as photons.

• Time > 0.001 sec:

Quarks combined to form protons & neutrons


Protons and NeutronsAre Composed of 3 Quarks


Era of Nucleosynthesis (t < 3 min)

• Protons & neutrons fuse ! 4p He• Some He nuclei torn apart by the high temperatures

• When Universe was 3 min old, it had cooled to 109 K.• At this point, the fusion stopped

• Afterwards, the matter in the Universe was:• 70% Hydrogen nuclei (i.e. individual protons)• 25% Helium nuclei• trace amounts of Deuterium (H isotope) & Lithium nuclei


History of the Universe


The Universe since the Big Bang: Gravitational Attraction of material

Billions of years ago


Era of Galaxies ( t > 109 yr)

• The first galaxies came into existence about 1 billion years after the Big Bang.

• This is the current era of the Universe.


The Fate of the Sun&

The Origin of Atoms

End of Lecture 22

Lecture 22

© 2005 pearson education inc., publishing as addison-wesley the fate of our sun & the origin of...

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