Astronomy 1020-H Stellar Astronomy Spring_2015 Day-29

Course Announcements Smartworks Chapter 14: Friday 2 Dark night observing sessions left: Mon. Apr. 13 & Thurs. Apr. 16 Reports are due Wed. Apr. 22 Solar Rotation Project due Mon. Apr. 27 Exam-3: Fri. 4/10

Astronomy in the Fall, 2015 ASTR-1010/ Planetary Astronomy + Lab (H,R) ASTR-1020/ Stellar Astronomy + Lab (R) ASTR Problems in Planet Astronomy ASTR Intro. to Observational Astronomy ASTR-4000/4001 – Astrophotography & Lab ASTR-4170 – Special Topics in Astronomy Photometry and Filter Systems TR; 3:30-5:00; B310

Atomic Nuclei Nuclei consist of protons and neutrons. Protons: positive electrical charge. Neutrons: no electrical charge. Electrical forces push protons apart. The strong nuclear force binds protons together. Fusion requires ramming protons together at high speed (i.e., at high temperature).

Isotopes of Hydrogen and Helium Number of protons sets the type of atom. Isotopes: Number of neutrons can vary. Hydrogen (H): one proton. Ordinary H: no neutrons ( 1 H). Deuterium: one proton, one neutron ( 2 H). Helium (He): two protons. Ordinary helium: two protons, two neutrons ( 4 He). Helium-3: two protons, one neutron ( 3 He).

The Periodic Table

 Nuclear fusion involves the fusing of atomic nuclei.  Nuclei consist of protons and neutrons.  Protons: positive electrical charge.  Neutrons: no electrical charge.  Electrical forces push protons apart.

 The strong nuclear force binds protons and neutrons together.  Fusion requires ramming protons together at high speed (i.e., at high temperature).  Creates more massive nuclei from less massive ones.

Powering the Sun  The Sun has existed for about 4.6 billion years.  The Sun must therefore generate a lot of energy over a long time.  Source: fusion of hydrogen into helium in the central core.  This fusion is often called hydrogen burning.  All main sequence stars are powered by the fusion of hydrogen into helium, which generates energy.

Fusion and Energy  Mass of four hydrogen (H) nuclei is times greater than 1 helium (He) nucleus.  Relativity: mass and energy are equivalent: E = mc 2 or m = E/c 2  Difference in mass is released as energy in this very efficient process.  Fusion takes place in the core, where it is hot enough (15 million K).  Fusion process in the Sun: proton-proton chain.

Testing Models of the Sun Hydrogen fusion emits neutrinos. Neutrinos: light atomic particles, no charge. Very weak interactions with matter. Can measure the rate they arrive at Earth. Rate agrees with predictions and with experiments on neutrino physics.

Solar Neutrinos

 Hydrogen fusion emits neutrinos: light atomic particles, no charge.  Very weak interactions with matter.  Should escape the core freely.

 Can measure the rate and types that arrive at Earth (they can change flavors).  Rate agrees with predictions and with experiments on neutrino physics.

 Neutrino detectors are atypical telescopes.  Today they use vast quantities of ice or ultra- pure water: Scientists wait for neutrinos to interact, generating a detectable signal. CONNECTIONS 14.2

The Proton-Proton Chain

 The Sun produces energy from nuclear fusion.  The mass of four hydrogen nuclei is larger than one helium nucleus by 4.39 x kg.  The energy associated with that is:  The Sun consumes hydrogen at a rate of 600 billion kilograms per second, so each year the Sun consumes: MATH TOOLS 14.1

 The Sun’s fusion process is the proton-proton chain: a three-step process to turn 4 hydrogen nuclei into 1helium nucleus and energy.  Also creates positrons and neutrinos. CONNECTIONS 14.1 Animation

Concept Quiz—Fusion Where does nuclear fusion take place in the Sun? A.in the core B.in the radiative zone C.in the convective zone D.in the corona

 Energy produced in the core must get out.  Inner part of the Sun: radiative zone.  Radiative transfer: Hotter photons move out from the core.  The opacity of a material can impede this.

 Conditions change as the photons move out.  Outer part: convective zone.  Convection (rising/falling of hot/cool gas).  Surface: radiation emitted into space.  Energy from the core takes 10 5 years to reach the outer layers.

Energy Transport Mechanisms of moving energy: Radiative transfer (photons). Convection (rising/falling of hot/cool gas). Inner part of the Sun: radiative zone. Outer part: convective zone. Surface: radiation emitted into space. Energy from the core takes 10 5 years to reach the surface.