© 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 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

© 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 The chemical enrichment of our Galaxy The Big Bang: Origin of H and He The Death of our Sun and other Stars The chemical enrichment of our Galaxy The Big Bang: Origin of H and He Lecture 23

© 2005 Pearson Education Inc., publishing as Addison-Wesley You can measure the amount of different atoms from darkness of the absorption lines. Dark spectral lines are caused by absorption of light by atoms in the Sun’s atmosphere. Chemical Composition of the Sun Magnesium Sodium Calcium Iron

© 2005 Pearson Education Inc., publishing as Addison-Wesley 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’s The Elements Tom Lehrer singing it: Missing Lawrencium. Listen for Berkelium and Californium © 2005 Pearson Education Inc., publishing as Addison-Wesley

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

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Mass Input: 4 p Mass Output: 1 He (2p + 2n) Look up Masses of particles: Mass Input = Mass Output Mass is missing ! Converted to Energy: E = mc 2 Luminosity of Sun: Nuclear Burning of H to He Hydrogen is converted to Helium in Sun-like stars.

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Death of the Sun in 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”

© 2005 Pearson Education Inc., publishing as Addison-Wesley Giant Star Phase The He core collapses until it heats to 10 8 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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Fusion of 3 helium nuclei into Carbon “Triple-Alpha “

© 2005 Pearson Education Inc., publishing as Addison-Wesley Planetary Nebula When the Giant star exhausts its Helium fuel in the central core: –the Carbon core collapses. –Low & solar-mass stars –Low & solar-mass stars don’t have enough gravitational energy to heat to 6 x 10 8 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”.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Planetary Nebulae Cat’s Eye Nebula Twin Jet Nebula

© 2005 Pearson Education Inc., publishing as Addison-Wesley Planetary Nebulae Ring Nebula Hourglass Nebula The collapsing Carbon core becomes a White Dwarf

© 2005 Pearson Education Inc., publishing as Addison-Wesley When High Mass Stars Die: Supergiants They Contract, heat up to 600 million K. –C fuses into O. They exhaust H fuel. He C.

© 2005 Pearson Education Inc., publishing as Addison-Wesley When High Mass Stars Die: Supergiants They Contract, heat up to 600 million K. –C fuses into O. C is exhausted, core collapses until O fuses. The cycle repeats itself. –O burns to Ne. They exhaust H fuel. He C.

© 2005 Pearson Education Inc., publishing as Addison-Wesley When High Mass Stars Die: Supergiants They Contract, heat up to 600 million K. –C fuses into O. C is exhausted, core collapses until O fuses. The cycle repeats itself. –O burns to Ne. –Ne burns to Mg. They exhaust H fuel. He C.

© 2005 Pearson Education Inc., publishing as Addison-Wesley When High Mass Stars Die: Supergiants They Contract, heat up to 600 million K. –C fuses into O. C is exhausted, core collapses until O fuses. The cycle repeats itself. –O burns to Ne. –Ne burns to Mg. –Mg burns to Si. –Si burns to Fe. They exhaust H fuel. He C.

© 2005 Pearson Education Inc., publishing as Addison-Wesley When High Mass Stars Die: Supergiants They Contract, heat up to 600 million K. –C fuses into O. C is exhausted, core collapses until O fuses. The cycle repeats itself. –O burns to Ne. –Ne burns to Mg. –Mg burns to Si. –Si burns to Fe. They exhaust H fuel. He C.

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

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Supernova Explosions Crab Nebula in Taurus supernova exploded in 1054 The explosion brings temperature to Billions 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

© 2005 Pearson Education Inc., publishing as Addison-Wesley Supernovae Veil Nebula Tycho’s Supernova (X-rays) exploded in 1572

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

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

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

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley 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). The Origin of the Atomic Elements

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

© 2005 Pearson Education Inc., publishing as Addison-Wesley 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). The Origin of the Atomic Elements

© 2005 Pearson Education Inc., publishing as Addison-Wesley Where did all the Hydrogen and Helium Come from? The 92 atomic elements were all constructed in the centers of stars (except hydrogen, helium and lithium). The Origin of the Atomic Elements

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

Depiction of Big Bang

© 2005 Pearson Education Inc., publishing as Addison-Wesley t < sec Quarks and Electrons as numerous as photons. (No Protons or neutrons: At billions of degrees,any protons collide, break apart into quarks.)

© 2005 Pearson Education Inc., publishing as Addison-Wesley Quarks and Photons Annihilate: Equilibrium

© 2005 Pearson Education Inc., publishing as Addison-Wesley t < sec Quarks and Electrons as numerous as photons. Time > sec: Quarks combined to form protons & neutrons

© 2005 Pearson Education Inc., publishing as Addison-Wesley Protons and Neutrons Are Composed of 3 Quarks

© 2005 Pearson Education Inc., publishing as Addison-Wesley 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 10 9 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

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

History of the Universe © 2005 Pearson Education Inc., publishing as Addison-Wesley

The Universe since the Big Bang: Gravitational Attraction of material Billions of years ago

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Universe since the Big Bang: Gravitational Attraction of material Billions of years ago

© 2005 Pearson Education Inc., publishing as Addison-Wesley Era of Galaxies ( t > 10 9 yr) The first galaxies came into existence about 1 billion years after the Big Bang. This is the current era of the Universe.

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

The Fate of the Sun & The Origin of Atoms End of Lecture 22 Lecture 22