DOCSLIB.ORG

Magnetic Confinement of the Solar Tachocline: II. Coupling to a Convection Zone A

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Magnetic Confinement of the Solar Tachocline: II. Coupling to a Convection Zone A Magnetic confinement of the solar tachocline: II. Coupling to a convection zone A. Strugarek, A.S. Brun, J.-P. Zahn To cite this version: A. Strugarek, A.S. Brun, J.-P. Zahn. Magnetic confinement of the solar tachocline: II. Coupling to a convection zone. Astronomy and Astrophysics - A&A, EDP Sciences, 2011, 532, pp.A34. 10.1051/0004-6361/201116518. cea-00828296 HAL Id: cea-00828296 https://hal-cea.archives-ouvertes.fr/cea-00828296 Submitted on 22 Jul 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Astronomy & Astrophysics manuscript no. Magnetic˙Confinement_TachoclineII_arxiv c ESO 2018 October 12, 2018 Magnetic confinement of the solar tachocline: II. Coupling to a convection zone A. Strugarek1, A. S. Brun1 and J.-P. Zahn2;1 1 Laboratoire AIM Paris-Saclay, CEA/Irfu Universit´eParis-Diderot CNRS/INSU, F-91191 Gif-sur-Yvette, France 2 LUTH, Observatoire de Paris, CNRS-Universit´eParis Diderot, Place Jules Janssen, 92195 Meudon, France Received 14 january 2011 / Accepted 12 June 2011 ABSTRACT Context. The reason for the observed thinness of the solar tachocline is still not well understood. One of the explanations that have been proposed is that a primordial magnetic field renders the rotation uniform in the radiation zone. Aims. We test here the validity of this magnetic scenario through 3D numerical MHD simulations that encompass both the radiation zone and the convection zone. Methods. The numerical simulations are performed with the anelastic spherical harmonics (ASH) code. The computa- tional domain extends from 0:07 R to 0:97 R . Results. In the parameter regime we explored, a dipolar fossil field aligned with the rotation axis cannot remain confined in the radiation zone. When the field lines are allowed to interact with turbulent unstationary convective motions at the base of the convection zone, 3D effects prevent the field confinement. Conclusions. In agreement with previous work, we find that a dipolar fossil field, even when it is initially buried deep in- side the radiation zone, will spread into the convective zone. According to Ferraro's law of iso-rotation, it then imprints on the radiation zone the latitudinal differential rotation of the convection zone, which is not observed. Key words. Sun: interior { Sun: rotation { Magnetohydrodynamics { Convection { Magnetic Fields 1. Introduction because Miesch (2003) found in his numerical simulations that this turbulence is indeed anti-diffusive in the verti- The discovery of the solar tachocline can be considered as cal direction, but the shear is reduced in latitude. Similar one of the great achievements of helioseismology (see Brown conclusions were reached through theoretical (analytical) et al. 1989). In this layer the rotation switches from differ- studies by Kim (2005), Leprovost & Kim (2006), and Kim ential (i.e., varying with latitude) in the convection zone & Leprovost (2007). to nearly uniform in the radiation zone below. Its extreme thinness (less than 5 % of the solar radius) came as a sur- Gough & McIntyre proposed an alternate model, in prise (see Charbonneau et al. 1999) and has still not been which a primordial magnetic field is buried in the radia- explained properly. tive zone and inhibits the spread of the tachocline. This is Spiegel & Zahn (1992) made the first attempt to model achieved through a balance between the confined magnetic the tachocline, and they showed that it should spread deep field and a meridional flow pervading the base of the convec- into the radiation zone owing to thermal diffusion. As a re- tion zone. Such a fossil field was also invoked by Rudiger & Kitchatinov (1997) to explain the thinness of the tachocline sult, the differential rotation should extend down to 0:3 R after 4:5 Gyr, contrary to what is inferred from helioseis- and by Barnes et al. (1999) to interpret the lithium-7 de- mology (Schou et al. 1998; Thompson et al. 2003). The au- pletion at the solar surface. Moreover, it would easily ac- thors suggested one way to confine the tachocline, namely count for the quasi uniform rotation of the radiative inte- to counter-balance thermal diffusion by an anisotropic tur- rior, which the hydrodynamic model of Spiegel & Zahn does bulence, which would smooth the differential rotation in not (at least in its original formulation). However, one may latitude. This model was successfully simulated in 2D by expect that such a field would spread by ohmic diffusion, arXiv:1107.3665v1 [astro-ph.SR] 19 Jul 2011 Elliott (1997). and that it would eventually connect with the convection Gough & McIntyre (1998) (GM98 hereafter) argued zone, thus imposing the differential rotation of that zone that such an anisotropic turbulent momentum transport is on the radiation zone below. not able to erode a large-scale latitudinal shear, citing ex- In order to test the magnetic confinement scenario and amples from geophysical studies (see Starr 1968 and more to put constraints on the existence of such a primordial recently Dritschel & McIntyre 2008 for a comprehensive field, several numerical simulations of the solar radiation review). For instance, the quasi-biennal oscillation in the zone were performed by Garaud (2002) in 2D, and by Brun Earth's stratosphere arises from the anti-diffusive behavior & Zahn (2006) (i.e. paper I, hereafter BZ06) in 3D. These of anisotropic turbulence. But the question is hardly settled simulations exhibit a propagation of the differential rota- tion into the radiation zone (primarily in the polar region). Send offprint requests to: A. Strugarek The primordial magnetic field successfully connects to the e-mail: [email protected] base of the convection zone where the shear is imposed 2 Strugarek, Brun, & Zahn: Magnetic confinement of the tachocline : II. Coupling to a convection zone and, according to Ferraro's law of iso-rotation (Ferraro In the present work, we start our simulation from a ma- 1937), the angular velocity is transmitted along the mag- ture model with a convection and a radiation zone. We then netic field lines from the convection zone into the radiative introduce an axisymmetric dipole-like magnetic field deep interior, much faster than it would through thermal diffu- in the inner radiation zone. This work is meant to explore sion. However, in the aforementioned calculations the base further the mechanisms considered in BZ06. The system is of the convection zone was treated as an impenetrable wall, then evolved self-consistently through the interplay of fluid i.e. radial motions could not penetrate in either direction and magnetic field dynamics. As in Brun et al. (2011), the (from top down or from bottom up). No provision was made computational domain extends from rbottom = 0:07R to for a meridional circulation originating in the convection rtop = 0:97R , and the boundary between radiation and zone that would penetrate into the radiation zone and could convection zone is defined at rbcz ∼ 0:715 R , based on prevent the upward spread of the magnetic field. This pene- the initial entropy profile (see Figs. 1(a) and 1(c)) that tration was taken into account in numerical simulations by is assumed to setup the background equilibrium state. We Sule et al. (2005), Rudiger & Kitchatinov (2007), Garaud also define in Fig. 1(c) the convective overshooting depth & Garaud (2008), in a model of the polar region by Wood rov ∼ 0:675 R (see Sect. 2.2), the penetration depth of the & McIntyre (2007), and in simulations coupling the radia- meridional circulation rMC ∼ 0:68 R (see Sect. 3.2), and tive zone to a convective zone by Rogers (2011) to prop- the shear depth rshear ∼ 0:58 R (see Sect. 2.2). erly represent the GM98 scenario. In most of these models, an axisymmetric and stationary meridional circulation was The diffusivities (Fig. 2) were chosen to achieve a realis- imposed at the top of the radiation zone, strong enough tic rotation profile in the convective envelope (see Sect. 2.2) to bend the magnetic field lines of the primordial field. As by means of an efficient angular momentum redistribution could be expected, various profiles of meridional circulation by Reynolds stresses (Brun & Toomre 2002; Miesch et al. resulted in different confinement properties, thus emphasiz- 2006). In the radiation zone, they have the same values as in ing the need for a more self-consistent approach. We thus BZ06 for consistency with previous studies. We define the propose here to treat the problem by letting a genuine con- following step function to construct our diffusivity profiles: vective envelope dynamically generate its meridional cir- culation and differential rotation and to study how these nonlinearly generated flows interact with a fossil field. 1 r − r step(r) = 1 + tanh 10−10 ν ; Our 3D simulations treat the nonlinear coupling of the 2 νs convection and radiation zones, and the model includes all ν = ν ν + ν (1 − ν ) step; (1) physical ingredients that play a role in the tachocline con- e t t e finement (thermal and viscous diffusion, meridional circula- tion, convective penetration, solar-like stratification, mag- 10 netic fields, pumping, ...). The paper is organized as follows. where rν = 4:7 10 cm and νs = 0:1 control the radial In Sect. 2 we describe the model we use to address the ques- localization and the thickness of the diffusivity jump. The 12 2 −1 tion of the magnetic confinement of the tachocline.
Load more

Recommended publications
  • Institute for Nuclear Study University of Tokyo Tanashi, Tokyo 188, Japan And
    lNS-Rep.-645 INSTITUTE FOR NUCLEAR STUDY . UNIVERSITY OF TOKYO Sept 1987 Tanashi, Tokyo 188 Japan Resonant Spin-Flavor Precession of k Solar and Supernova Neutrinos Chong-Sa Lim and William J. Marciano •3300032376 INS-Rep.-645 Sept. 1987 Resonant Spin-Flavor Precession of Solar and Supernova Neutrinos Chong-Sa Lin Institute for Nuclear Study University of Tokyo Tanashi, Tokyo 188, Japan and William J. Mareiano Brookharen National Laboratory Upton. New Kork 11973, U.S.A. Abstract: The combined effect of natter and aagnetic fields on neutrino spin and flavor precession is examined. We find a potential new kind of resonant solar neutrino conversion \>_ * eL v or vT (for Dirac neutrinos) or «e *• « or vT (for Hajorana R R neutrinos). Such a resonance could help account for the lower than' expected solar neutrino v flux and/or Indications of an antl-oorrelatlon between fluctuations in the v( flux and sunspot activity. Consequences of spin-flavor precession for supernova neutrinos are also briefly discussed. - 1 - There has been a longstanding disagreement between the solar neutrino v_ flux monitored by B. Davis"" and collaborators Average Flux - 2.1 i 0.3 SHU , (1) (1 SNU - 10*' captures/s-atom) 7 37 via the reaction \>e • ' Cl •• «" • Ar and Bahcall'a standard solar model prediction Predicted Flux - 7.9 ± 2.5 SNU <3o errors) . <2) That discrepancy has come to be known as the solar neutrino puzzle. Attempts to resolve It have given rise to many speculative Ideas about unusual properties of neutrinos and/or the solar interior. One rather recently proposed solution, the MSW"-' (Mlkheyev, Snlrnov, Wolfensteln) effect is particularly elegant.
    [Show full text]
  • Doc.10100.Space Weather Manual FINAL DRAFT Version
    Doc 10100 Manual on Space Weather Information in Support of International Air Navigation Approved by the Secretary General and published under his authority First Edition – 2018 International Civil Aviation Organization TABLE OF CONTENTS Page Chapter 1. Introduction ..................................................................................................................................... 1-1 1.1 General ............................................................................................................................................... 1-1 1.2 Space weather indicators .................................................................................................................... 1-1 1.3 The hazards ........................................................................................................................................ 1-2 1.4 Space weather mitigation aspects ....................................................................................................... 1-3 1.5 Coordinating the response to a space weather event ......................................................................... 1-3 Chapter 2. Space Weather Phenomena and Aviation Operations ................................................................. 2-1 2.1 General ............................................................................................................................................... 2-1 2.2 Geomagnetic storms ..........................................................................................................................
    [Show full text]
  • Stability of Toroidal Magnetic Fields in Rotating Stellar Radiation Zones
    A&A 478, 1–8 (2008) Astronomy DOI: 10.1051/0004-6361:20077172 & c ESO 2008 Astrophysics Stability of toroidal magnetic fields in rotating stellar radiation zones L. L. Kitchatinov1,2 and G. Rüdiger1 1 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482, Potsdam, Germany e-mail: [lkitchatinov;gruediger]@aip.de 2 Institute for Solar-Terrestrial Physics, PO Box 291, Irkutsk 664033, Russia e-mail: [email protected] Received 26 January 2007 / Accepted 14 October 2007 ABSTRACT Aims. Two questions are addressed as to how strong magnetic fields can be stored in rotating stellar radiation zones without being subjected to pinch-type instabilities and how much radial mixing is produced if the fields are unstable. Methods. Linear equations are derived for weak disturbances of magnetic and velocity fields, which are global in horizontal dimen- sions but short–scaled in radius. The linear formulation includes the 2D theory of stability to strictly horizontal disturbances as a special limit. The eigenvalue problem for the derived equations is solved numerically to evaluate the stability of toroidal field patterns with one or two latitudinal belts under the influence of rigid rotation. Results. Radial displacements are essential for magnetic instability. It does not exist in the 2D case of strictly horizontal disturbances. Only stable (magnetically modified) r-modes are found in this case. The instability recovers in 3D. The minimum field strength Bmin for onset of the instability and radial scales of the most rapidly growing modes are strongly influenced by finite diffusion, the scales are indefinitely short if diffusion is neglected. The most rapidly growing modes for the Sun have radial scales of about 1 Mm.
    [Show full text]
  • The Sun: Our Star (Chapter 14) Based on Chapter 14
    The Sun: Our Star (Chapter 14) Based on Chapter 14 • No subsequent chapters depend on the material in this lecture • Chapters 4, 5, and 8 on “Momentum, energy, and matter”, “Light”, and “Formation of the solar system” will be useful for understanding this chapter. Goals for Learning • What is the Sun’s structure? • How does the Sun produce energy? • How does energy escape from the Sun? • What is solar activity? What Makes the Sun Shine? • Sun’s size/distance known by 1850s • Some kind of burning, chemical reaction? – Can’t provide enough energy • Gravitational potential energy from contraction? – Sun doesn’t shrink very fast, shines for 25 million years • Physicists like this idea. Geologists don’t, because rocks/fossils suggest age of 100s of millions of years E=mc2 (1905, Einstein) • Massive Sun has enough energy to shine for billions of years, geologists are happy • But how does “m” become “E”? Sun is giant ball of plasma (ionized gas) Charged particles in plasma are affected by magnetic fields Magnetic fields are very important in the Sun Sun = 300,000 ME Sun >1000 MJ Radius = 700,000 km Radius > 100 RE 3.8 x 1026 Watts Rotation: 25 days (Equator) Rotation: 30 days (Poles) Surface T = 5,800 K Core T = 15 million K 70% Hydrogen, 28% Helium, 2% heavier elements Solar Wind • Stream of charged particles blown continually outwards from Sun • Shapes the magnetospheres of the planets today • Cleared away the gas of the solar nebula 4.5 billion years ago Corona • Low density outer layer of Sun’s atmosphere • Extends several million km high • T = 1 million K (why?) • Source of solar X-ray emissions – what wavelength? X-ray image of solar corona.
    [Show full text]
  • Chapter 15--Our
    2396_AWL_Bennett_Ch15/pt5 6/25/03 3:40 PM Page 495 PART V STELLAR ALCHEMY 2396_AWL_Bennett_Ch15/pt5 6/25/03 3:40 PM Page 496 15 Our Star LEARNING GOALS 15.1 Why Does the Sun Shine? • Why was the Sun dimmer in the distant past? • What process creates energy in the Sun? • How do we know what is happening inside the Sun? • Why does the Sun’s size remain stable? • What is the solar neutrino problem? Is it solved ? • How did the Sun become hot enough for fusion 15.4 From Core to Corona in the first place? • How long ago did fusion generate the energy we 15.2 Plunging to the Center of the Sun: now receive as sunlight? An Imaginary Journey • How are sunspots, prominences, and flares related • What are the major layers of the Sun, from the to magnetic fields? center out? • What is surprising about the temperature of the • What do we mean by the “surface” of the Sun? chromosphere and corona, and how do we explain it? • What is the Sun made of? 15.5 Solar Weather and Climate 15.3 The Cosmic Crucible • What is the sunspot cycle? • Why does fusion occur in the Sun’s core? • What effect does solar activity have on Earth and • Why is energy produced in the Sun at such its inhabitants? a steady rate? 496 2396_AWL_Bennett_Ch15/pt5 6/25/03 3:40 PM Page 497 I say Live, Live, because of the Sun, from some type of chemical burning similar to the burning The dream, the excitable gift.
    [Show full text]
  • Radiation Zone
    AST 100 General Astronomy: 5. What’s inside the Sun? Stars & Galaxies From the Center Outwards • Core: Hydrogen fusing into helium, releasing energy in ANNOUNCEMENTS the form of gamma rays, neutrinos, and positrons Midterm I on Tue, Sept. 29 it will cover class material up to today (included) • Core temp = 15 million K, hot & dense from the gravitational Quiz #2 today, end of class weight of all that mass Meanderings of outbound photons Our gamma-ray photons random walk outwards (getting Radiation Zone redirected with every step), gradually cooling • Gamma ray photons leave the core and move into an area known as the Takes hundreds of Radiation Zone thousands to a million – Neutrinos? They leave right years to get out!! away, no interaction – Positrons? Quickly find electrons in the core to annihilate with. • Photons only travel about 1 mm before being redirected in another direction T=10 million K. Photosphere Convection Zone • At the top of the convection • Eventually, gas is cool zone, the densities are now enough (2 million K at the low enough that our boundary) and becomes photons can zoom away. turbulent – Now downgraded all the – No longer just redirects way to visible energies photons, now absorbs them • Photosphere is the “visible surface” of the Sun • Convection: hotter • T = only 5800 K regions rise, cooler • Photons free - seen at Earth regions sink 8 min later • Blackbody spectrum (T= • Energy continues to work 5800 K) + absorption from its way out - nearly 1 cooler gasses just on top million years to get out Granulation: turbulent convection Granulation Movie Appearance of the photosphere • Typical granulations last only 8 - 15 minutes • Movie covers 35 min Taken by G.
    [Show full text]
  • The Sun Worksheet
    Name ____________________________ Date ____________________ Class ____________ The Solar System The Sun Guide for Reading ■ What are the three layers of the sun’s interior? ■ What are the three layers of the sun’s atmosphere? ■ What features form on or above the sun’s surface? The sun’s mass is 99.8 percent of all the mass in the solar system. Because the sun is so large, its gravity is strong enough to hold all of the planets and other distant objects in orbit. Unlike Earth, the sun does not have a solid surface. Like Earth, the sun has an interior and an atmosphere. The sun’s interior consists of the core, radiation zone, and convection zone. Each layer has different properties. The sun produces an enormous amount of energy in its core, or central region. The sun’s energy comes from nuclear fusion. In the process of nuclear fusion, hydrogen atoms in the sun join to form helium. The light and heat produced by the sun’s core first pass through the middle layer of the sun’s interior, the radiation zone. The radiation zone is a region of very tightly packed gas where energy is transferred mainly in the form of electromagnetic radiation. The convection zone is the outermost layer of the sun’s interior. Hot gases rise from the bottom of the convection zone and gradually cool as they approach the top. Cooler gases sink, forming loops of gas that move heat toward the sun’s surface. The sun’s atmosphere consists of the photosphere, the chromosphere, and the corona.
    [Show full text]
  • Dynamics of the Earth's Radiation Belts and Inner Magnetosphere Newfoundland and Labrador, Canada 17 – 22 July 2011
    AGU Chapman Conference on Dynamics of the Earth's Radiation Belts and Inner Magnetosphere Newfoundland and Labrador, Canada 17 – 22 July 2011 Conveners Danny Summers, Memorial University of Newfoundland, St. John's (Canada) Ian Mann, University of Alberta, Edmonton (Canada) Daniel Baker, University of Colorado, Boulder (USA) Program Committee David Boteler, Natural Resources Canada, Ottawa, Ontario (Canada) Sebastien Bourdarie, CERT/ONERA, Toulouse (France) Joseph Fennell, Aerospace Corporation, Los Angeles, California (USA) Brian Fraser, University of Newcastle, Callaghan, New South Wales (Australia) Masaki Fujimoto, ISAS/JAXA, Kanagawa (Japan) Richard Horne, British Antarctic Survey, Cambridge (UK) Mona Kessel, NASA Headquarters, Washington, D.C. (USA) Craig Kletzing, University of Iowa, Iowa City (USA) Janet Kozy ra, University of Michigan, Ann Arbor (USA) Lou Lanzerotti, New Jersey Institute of Technology, Newark (USA) Robyn Millan, Dartmouth College, Hanover, New Hampshire (USA) Yoshiharu Omura, RISH, Kyoto University (Japan) Terry Onsager, NOAA, Boulder, Colorado (USA) Geoffrey Reeves, LANL, Los Alamos, New Mexico (USA) Kazuo Shiokawa, STEL, Nagoya University (Japan) Harlan Spence, Boston University, Massachusetts (USA) David Thomson, Queen's University, Kingston, Ontario (Canada) Richard Thorne, Univeristy of California, Los Angeles (USA) Andrew Yau, University of Calgary, Alberta (Canada) Financial Support The conference organizers acknowledge the generous support of the following organizations: Cover photo: Andy Kale ([email protected])
    [Show full text]
  • The Science of the Sun by Cindy Grigg
    The Science of the Sun By Cindy Grigg 1 Photo credit: NASA 2 Our sun is a star. Like all stars, it is a mass of very hot gases. On Earth, burning fossil fuels like gasoline or coal gives us energy for our cars and heating our homes. But the sun's energy doesn't come from burning fuels. The sun's energy comes from nuclear fusion. The nuclei (plural form of nucleus) of different atoms of gases in the sun fuse or join together. Most of the sun's fusion happens when atoms of hydrogen smash into each other. Under high pressure and at high temperatures, the atoms join or fuse together. This creates helium atoms. Every atom releases heat and light when it fuses with another atom. 3 How big is the sun? Its diameter, the distance across its center, is about 870,000 miles. That's more than one hundred times the diameter of Earth. The sun's volume is more than a million times the volume of Earth. Another way to say this is that the sun could hold one million Earths inside it. 4 The sun has different layers of gases. Each layer blends into the next, like the layers of Earth's atmosphere. The core is the center of the sun. Most of the sun's mass is in its core. The core is extremely dense. It is also very hot. Almost all fusion takes place in the core. 5 Energy created in the core moves outward. It passes next into the radiative or radiation zone.
    [Show full text]
  • 8. the Sun As a Star
    Astronomy 110: SURVEY OF ASTRONOMY 8. The Sun as a Star 1. Inside the Sun 2. Solar Energy 3. Solar Activity The Sun is not only the largest object in our solar system — it is also the nearest example of a star. It produces energy by converting hydrogen to helium, thereby maintaining a constant internal temperature. Particles emitted by the Sun and detected on Earth confirm the details of this picture. Radius: 6.9 × 108 m (109 times Earth) Mass: 2 × 1030 kg (300,000 Earths) Luminosity: 3.8 × 1026 watts Copyright © 2009 Pearson Education, Inc. Composition of the Sun Number of Chemical Atomic Atomic Atoms Symbol Number Weight 1,000,000 H 1 1 85,000 He 2 4 850 O 8 16 400 C 6 12 120 Ne 10 20 100 N 7 14 47 Fe 26 56 1. INSIDE THE SUN a. How Does the Sun Stay Hot? b. Two Kinds of Equilibrium c. Structure of the Sun How Does the Sun Stay Hot? Why does the Sun shine? Because it is hot! Copyright © 2009 Pearson Education, Inc. Is it on FIRE? … NO! Chemical Energy Content ~ 10,000 years Luminosity Copyright © 2009 Pearson Education, Inc. Is it CONTRACTING? … NO! Gravitational Potential Energy ~ 25 million years Luminosity Copyright © 2009 Pearson Education, Inc. E = mc2 —Einstein, 1905 It is powered by NUCLEAR ENERGY! Nuclear Potential Energy (core) ~ 10 billion years Luminosity Copyright © 2009 Pearson Education, Inc. Energy From Matter Matter is frozen energy, and each can be converted to the other. The “rate of exchange” is E = mc2 where c = 3 × 105 km/s is the speed of light.
    [Show full text]
  • Chapter 11: Our Star
    Lecture Outline Chapter 11: Our Star © 2015 Pearson Education, Inc. Why does the Sun shine? © 2015 Pearson Education, Inc. Is it on FIRE? … NO! Chemical Energy Content ~ 10,000 years Luminosity © 2015 Pearson Education, Inc. Is it CONTRACTING? … NO! Gravitational Potential Energy ~ 25 million years Luminosity © 2015 Pearson Education, Inc. E = mc2 —Einstein, 1905 It is powered by NUCLEAR ENERGY! Nuclear Potential Energy (core) ~ 10 billion years Luminosity © 2015 Pearson Education, Inc. Gravitational equilibrium: Gravity pulling in balances pressure pushing out. © 2015 Pearson Education, Inc. Energy balance: Thermal energy released by fusion in core balances radiative energy lost from surface. © 2015 Pearson Education, Inc. Gravitational contraction… provided energy that heated the core as the Sun was forming. Contraction stopped when fusion started replacing the energy radiated into space. © 2015 Pearson Education, Inc. What is the Sun's structure? © 2015 Pearson Education, Inc. 11.2 Nuclear Fusion in the Sun Our goals for learning: • How does nuclear fusion occur in the Sun? • How does the energy from fusion get out of the Sun? • How do we know what is happening inside the Sun? © 2015 Pearson Education, Inc. Fission Fusion Big nucleus splits into Small nuclei stick together smaller pieces. to make a bigger one. (Nuclear power plants) (Sun, stars) © 2015 Pearson Education, Inc. High temperatures enable nuclear fusion to happen in the core. © 2015 Pearson Education, Inc. The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus. © 2015 Pearson Education, Inc. IN 4 protons OUT 4He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower.
    [Show full text]
  • Neutron Star
    Chapter 10 Our Star X-ray visible Radius: 6.9 108 m (109 times Earth) Mass: 2 1030 kg (300,000 Earths) Luminosity: 3.8 1026 watts (more than our entire world uses in 1 year!) Why does the Sun shine? Is it on FIRE? Is it on FIRE? Chemical Energy Content (J) ~ 10,000 years Luminosity (J/s = W) Is it on FIRE? … NO Chemical Energy Content ~ 10,000 years Luminosity Is it CONTRACTING? Is it CONTRACTING? Gravitational Potential Energy ~ 25 million years Luminosity Is it CONTRACTING? … NO Gravitational Potential Energy ~ 25 million years Luminosity E = mc2 —Einstein, 1905 It is powered by NUCLEAR ENERGY! Nuclear Potential Energy (core) ~ 10 billion years Luminosity E = mc2 —Einstein, 1905 It is powered by NUCLEAR ENERGY! •Nuclear reactions generate the Sun’s heat •But they require very high temperatures to begin with •Where do those temperatures come from? •They come from GRAVITY! •The tremendous weight of the Sun’s upper layers compresses interior •The intense compression generates temperatures >107 K in the innermost core •And that’s where the nuclear reactions are Gravitational Equilibrium •The compression inside the Sun generates temperatures that allow fusion •The fusion reactions in turn generate outward pressure that balances the inward crush of gravity •The Sun is in a balance between outward pressure from fusion and inward pressure from gravity •This is called gravitational equilibrium The Sun’s Structure Solar wind: A flow of charged particles from the surface of the Sun Corona: Outermost layer of solar atmosphere Temp ~1 million
    [Show full text]