Stellar Energy and Nucleosynthesis

Transcription

1 Stellar Energy and Nucleosynthesis Lecture 13 1

2 Orion Mosaic Orion in the Infrared Cornell imaging of Orion from SOFIA 19.7 mm (green) & 37 mm (red) 2

3 Orion Full OMC Prolyds 1 3

4 OMC Prolyds 2 HH 32 HH 32 Young stars have jets/outflows Blue: SII Green: H-alha Red: R-band 4

5 T Tauri stars Named after the first one found. Newly formed stars which are just clearing away the surrounding material. Surface erutions, raid variations of light outut and mass loss via a wind Many are surrounded by disks!! Could lanets be forming there? Sun was robably once a T Tauri star. Evolution/Origin of Outflows 5

6 What makes the Sun shine? The Sun emits 4 x Watts Peole ower about 600 billion Watts US Power consumtion about Watts Equivalent to >100 billion nuclear bombs/sec! We know from dating of rocks on the Earth and Moon, that the Sun is at least 4.5 billion years old. Need about 6x10 43 J of energy Possible energy sources for stars* Chemical Reactions Such as a burning fire Sun s lifetime would be ~1000 years!! Gravitational Comression Shrinking use gravity, like a water fall Must collase ~50 feet er year! Sun s lifetime would be ~15x10 6 years. Nuclear reactions Convert mass to energy Much more energy er unit mass than chemical reactions *Main sequence stars 6

7 Conversion of Mass to Energy Albert Einstein Equivalence between mass and energy E = mc 2 Main-sequence stars release energy by converting Hydrogen into Helium 4 H 1 He 4 + energy Suerscrit is number of rotons + neutrons. Energy release from H He 4 H 1 = 6.693x10-27 kg 1 He 4 = 6.645x10-27 kg (mass) = 0.048x10-27 kg E = mc x10-12 Joules er reaction Energy is created out of mass! Converting the hydrogen into helium for the sun would roduce about J of energy. Enough to kee the Sun burning for about 10 billion years 7

8 Fusion and Fission Fusion is the rocess of creating heavier elements from lighter ones. e.g. 4 H 1 ==> He 4 + energy Fission is the breaking u of (tyically) heavy nuclei to make lighter ones. e.g. U n ==> Ba Kr n + energy Stars are fueled by Fusion Not enough heavy elements Stellar Cores T core ~ K Particles move very fast. collision The collision results in: Deuterium + Positron + Neutrino + Kinetic Energy 1H 2 + e + + n 8

9 The Neutrino A article roduced in stellar nuclear reactions is the neutrino, designated by the symbol n. n: has no charge & very small mass (close to zero) very little interaction with matter The Sun is transarent to neutrinos. Neutrino telescoes can look at the interior of the Sun. More than solar electron neutrinos ass through the human body every second. Original exeriment, tank of chlorine (cleaning fluid) in South Dakota mine. n s occasionally interact to convert 37 Cl to 37 Ar There aeared to be too few n s! This roblem was solved by the finding that neutrinos oscillate between three flavors (electron, muon, and tauon) as they ass through matter and sace In 2002 Nobel rize won by Ray Davis Jr. and Masatoshi Koshiba for studies of solar/cosmic neutrinos and first real time detection of suernova neutrinos, resectively Atomic Nuclei 1H 1 Hydrogen 1H 2 Deuterium 2He 3 Helium 3 2He 4 Helium 4 Proton Neutron 9

10 Reactions in stars Proton-Proton Chain Most efficient in lower mass stars T > 10,000,000 K CNO Cycle Most efficient in higher mass stars T > 16,000,000 K Hans Bethe (Cornell)

11 Proton-Proton Chain e + n 2 H 4 He 3 He g 3 He 11

12 CNO Cycle 12 C 4 He g 12 C 13 N e + n n 15 N 13 C 15 O 14 N e + g g Star stuff The conversion of H into He is not the only nuclear reaction than can take lace in stars. All elements other than H and He are roduced from stars (or exlosions of stars.) The material in you was formed by a star! The rocess of building u heavy elements from light ones is called nucleosynthesis. 12

13 Binding Energy er nuclear article 10/17/2012 Nucleosynthesis Formation of the elements. Heavy elements can only be formed from H and He at very high temeratures and densities. This can haen if the star is massive enough. The cores of giant and suergiant stars!! Energy from Fission and Fusion Hydrogen Fusion Fission Uranium Iron Atomic Mass 13

14 Binding Energy er nuclear article 10/17/2012 Turning to Iron The most stable element is Iron ( 26 Fe 56 ). For elements lighter than iron: Fusion releases energy For elements heavier than iron: Fission releases energy The universe is slowly turning to Iron! Energy from Fission and Fusion Hydrogen Fusion Fission Uranium Iron Atomic Mass 14

15 Trile Alha Process Nucleosynthesis 4 H 1 ==> He 4 He 4 + He 4 ==> Be 8 Be 8 + He 4 ==> C 12 C 12 + He 4 ==> O 16 O 16 + He 4 ==> Ne 20 Ne 20 + He 4 ==> Mg u to Fe 56 15

16 The core of an evolved star An element factory! An onion skin of different elements. An iron core - if star is massive enough. 16

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