ASTR730 / CSI661 Fall 2012 Jie Zhang Stellar Astrophysics An Introduction Aug. 28, 2012

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Transcript of ASTR730 / CSI661 Fall 2012 Jie Zhang Stellar Astrophysics An Introduction Aug. 28, 2012

  • ASTR730 / CSI661 Fall 2012 Jie ZhangStellar Astrophysics

    An Introduction

    Aug. 28, 2012

  • The Big Banghttp://rampant-mac.com/dp_07/Big-Bang-Theory_alt2_1920.jpg

  • History of the Universehttp://www.negotiationlawblog.com/Big%20Bang.jpg

  • Physical ForcesDepending on temperature (T) and density ()

  • Inflation occurs at 10-35 second after the Big Bang when temperature of universe dropped to 1027 K; at this temperature, strong force became distinct from the electromagnetic-weak force

    Before the inflation, the space is empty, filled with only virtual particles dictated by quantum mechanics

    Matter and energy of the universe is created during the inflation

    Just after the inflationary epoch, the universe was filled with particles, antiparticles and energetic gamma-ray photonsInflation

  • At t=10-6 second, the temperature in the universe dropped to the threshold temperature of 1013 K, at which the photons can not produce proton and anti-proton pairs (and neutron and anti-neutron pairs)At about t = 1 second, temperature fell below 6 X 109 K, electrons and positions annihilated to form low energy gamma-ray photons that can not reverse the processAs a result, matter and anti-matter content decreased, and radiation content increasedFrom 1 second to 380,000 years, the universe is dominated by the radiation (so called primordial fireball) derived from the annihilation of particles and antiparticles created early by the inflationCreate Radiation

  • If there had been perfect symmetry between particles and antiparticles, every particles would have been annihilated, leaving no matter at all in the universeThere are 109 photons in the microwave background for each proton/neutron in the universeTherefore, there is a slight but important asymmetry between matter and antimatterRight after the inflation, for every 109 antiprotons, there must have been 109 plus one ordinary protons, leaving one surviving after annihilationCreate Ordinary Matter

  • When the universe was 3 minutes older, the temperature was low enough to pass the deuterium (2H, one proton + one neutron) bottleneck to further produce helium

    At 15 minutes, the temperature of the universe is too low for any further nucleosynthesis

    Therefore, the relics of primordial fireball are hydrogen, helium (1 helium out of every 10 protons), and photons (1 billion photons for every proton)

    Heavier elements are formed later in the stars, not in the early universeRelics of primordial fireball

  • Recombination: at 377,000 years (T = 3000 K) after the Big Band, hydrogen (and helium) nuclei started to capture electrons to form neutral hydrogen (and helium) atoms. The photons mean free path becomes effectively infiniteAs a result of recombination, the universe has become transparent. This cosmic event is also called decouplingCosmic Microwave Background (CMB): the photons present at the time of decoupling are the same photons that we see in CMB. Therefore, CMB is a picture of the universe at the end of recombination epoch.CMB is observed as a spectrum of uniform black body thermal emission form all parts of the sky: T = 2.725 K, f = 160.2 GHz, and = 1.873 mmCosmic Microwave Background

  • Age: 13.7 billion yearsComposition: 73% dark energy, 23% dark matter, 4% ordinary matterThe State of the Universe

  • GalaxiesThis map shows 1.6 million galaxies from the 2MASS (Two-Micron All-Sky Survey) surveySupercluster of Galaxies lie along filaments

  • Galaxies

  • We are located in the middle of the Milky Way Galaxy

    28,000 light yearsfrom the center

    One of 200 billionstars in our GalaxyOur Galaxies

  • Interstellar gas and dust pervade the Galaxy Nebula: a cloud of concentrated interstellar gas and dust; 104 to 109 particles per cubic centimeterStar Formation: Nebula

  • Protostar: the clump formed from dense and cold nebula under gravitational contraction

    The protostar contracts, because the pressure inside is too low to support all the mass.

    As a protostar grows by the gravitational accretion of gases, Kelvin-Helmholtz contraction causes it to heat and begin glowing

    When its core temperatures become high enough to ignite steady hydrogen burning, it becomes a main sequence star

    Star Formation: Protostar

  • Star Formation: Protostar

  • A protostars relatively low temperature and high luminosity place it in the upper right region on an H-R diagramStar Formation

  • Stars

  • The SunSolar wind creates a big teardrop-shaped heliosphere around the solar system, by interacting with the interstellar wind

  • The Earth The Earth

    3rd planet from the Sun

    1 AU = 150 million km

    Travel time:By light --8 minutes

    By Solar Wind-- ~ 100 hrs

  • Credit: NASAThe Sun-Earth Connection

  • Space Weather: the ProcessIt starts from an eruption from the Sun.

    Prediction depends on how it propagates

  • Space Weather: effectsAurora; Geomagnetic StormFrom Space

  • Space Weather: effectsAdverse effectsDamaged transformerPower failure due to March 1989 storm

  • Space Weather: effectsOn Human Space ExplorationOn crew and passengers of polar-route airplanes

  • Space Weather: effectsOn Satellite Operation

  • Space Weather: effectsOn Communication and Navigation

  • PlanetComponents of Sun-EarthThe driver of Space WeatherCoronal mass ejections

  • PlanetComponents of Sun-EarthHeliosphere: solar windSpiral magnetic field: radial motion of solar wind combined with Suns rotation Sprinkler Analogy

  • PlanetComponents of Sun-EarthMagnetosphereA comet-shaped region around the Earth

  • PlanetComponents of Sun-EarthMagnetosphereElectric Currents in Magneto-sphere

  • PlanetComponents of Sun-EarthMagnetosphereEnergetic particles in Van Allen radiation belt

  • PlanetComponents of Sun-EarthIonosphereDensity fluctuation affects radio wave reflection and transmission

  • Recent MissionsHinode

  • Recent MissionsSTEREO

  • Recent MissionsSDO

  • The End

    ***********

    Plasma physics: plasma beta, coronal loopsB generation, distribution and energy storageRec: rapid energy releaseParticle Acceleration

    All these are fundamental processes in our universe: magnetosphere, heliosphere, solar atmosphere, galaxy.Important in laboratory toward solving energy problem *

    Plasma physics: plasma beta, coronal loopsB generation, distribution and energy storageRec: rapid energy releaseParticle Acceleration

    All these are fundamental processes in our universe: magnetosphere, heliosphere, solar atmosphere, galaxy.Important in laboratory toward solving energy problem ****************CME, flares. Particles (relativisit)*CME propagation, ICME*CME, flares. Particles (relativisit)*CME, flares. Particles (relativisit)*CME, flares. Particles (relativisit)*****