The Stars Chapter 14 Great Idea: The Sun and other stars use nuclear fusion reactions to convert mass into energy. Eventually, when a star s nuclear fuel is depleted, the star must burn out.
Chapter Outline The Nature of Stars The Anatomy of Stars The Variety of Stars The Life Cycles of Stars
iclicker Question How often do you look up at the night time sky? A Always (when possible) B Often C Sometimes D Never
iclicker Question Do you enjoy looking at the stars? A yes B no
The Nature of Stars
The Nature of Stars Astronomy Oldest science Star Fusion reactor in space Ball of gas All stars have a beginning and an ending
Measuring the Stars with Telescopes and Satellites Electromagnetic radiation Measurement of photons Wavelength Intensity Direction Variation
Telescopes
Orbiting Observatories Great Observatories Program Hubble Space Telescope Spitzer Infrared Telescope Chandra X-Ray Observatory
iclicker Question What source of data is used to analyze stars? A chemical testing of actual samples of stellar matter B electromagnetic radiation C spacecraft in orbit around distant stars D both B and C above E no data is used
iclicker Question Telescopes are devices that: A focus and concentrate radiation B magnify only visible light C all use mirrors D both B and C above
The Anatomy of Stars
Structure The Structure of the Sun Stellar core Radiative zone Convection zone Photosphere Chromosphere Corona Solar Wind Stream of particles
More On Solar Structure Hydrogen fusion takes place in a core extending from the Sun s center to about 0.25 solar radius The core is surrounded by a radiative zone extending to about 0.71 solar radius In this zone, energy travels outward through radiative diffusion The radiative zone is surrounded by a rather opaque convective zone of gas at relatively low temperature and pressure In this zone, energy travels outward primarily through convection
How do we know the Sun s interior? Helioseismology is the study of how the Sun vibrates These vibrations have been used to infer pressures, densities, chemical compositions, and rotation rates within the Sun
Magnetic Fields
Northern Lights (Aurora Borealis)
The Sun s Energy Source: Fusion Sun s Energy Source Historical Current hydrogen Fusion 3-steps-hydrogen burning 1) P + P D + e + + neutrino + energy 2) D + P 3 He + photon + energy 3) 3 He + 3 He 4 He + 2protons + photon + energy Life expectancy 11 billion years
The Variety of Stars Differences Color Brightness Distance Absolute brightness Energy output luminosity Apparent brightness Behavior Total mass age
Distance Light-years Measurement Triangulation (parallax) Spectroscopic parallax Cepheid variable Tully-Fisher Supernovae Type Ia Hubble s Law The Cosmic Distance Ladder
The Hertzsprung-Russel Diagram Star Groupings Main-sequence stars Red giants White dwarfs
Step 1 to an H-R Diagram Plot for the 20 nearest and brightest stars to Earth Absolute Magnitude Not an H-R Diagram 20 15 10 5 0 0 5000 10000 15000 20000 25000 30000-5 -10 Temperature
Step 2 to an H-R Diagram Reversing the y-axis -10 Getting Closer to an H-R Diagram Temperature (K) -5 Absolute Magnitude 0 5 10 15 20 0 5000 10000 15000 20000 25000 30000
Step 3 to an H-R Diagram Reversing the x-axis Lowest temperature to the right Now it's looking Like an H-R Diagram Temperature (K) -10-5 0 5 10 Absolute Magnitude 15 30000 25000 20000 15000 10000 5000 20 0
A Standard H-R Diagram
iclicker Question Compared with other stars, our Sun is: A an unusually large star B not a star at all C a rather ordinary star
iclicker Question The outer part of the Sun, the part that actually emits most of the light we see, is called the: A chromosphere B convective zone C photosphere D core E radiative zone
iclicker Question The solar wind is composed of: A bits of neutral gas B all kinds of organic substances C air D charged particles including hydrogen and helium ions
iclicker Question Northern lights result from interactions of: A the Sun s magnetic field with Earth s gravity B UV light from the Sun with Earth s ozone layer C the solar wind with the Earth s magnetic field
iclicker Question The Sun s peak output of energy is in: A the ultraviolet portion of the electromagnetic spectrum B the visible portion of the electromagnetic spectrum C the infrared portion of the electromagnetic spectrum
iclicker Question What is the Sun s energy source? A combustion of hydrogen rich chemical fuels B fusion of hydrogen C fission of hydrogen D radioactive decay E gravitational collapse
The Life Cycles of Stars
The Birth of Stars Nebular Hypothesis Laplace
The Main Sequence and the Death of Stars Stars much less massive than the sun Brown dwarf Glows 100 billion years No change in size, temperature, energy output
The Main Sequence and Stars about the mass of the sun Hydrogen burning at faster rate Move off main sequence Helium burning Red giant Begin collapse White dwarf the Death of Stars
The Life Cycle of a Star Like the Sun Gas cloud Fragmentation Protostar Kelvin-Helmholz contraction Hayashi Track Ignition Adjustment to Main Sequence Hydrogen Core Depletion Hydrogen shell burning Helium flash Helium core burning Helium core depletion Helium shell burning Helium shell flashes Planetary nebula White Dwarf
Sun s Life Cycle on H-R Diagram H-R Diagram with annotations for Stellar Stages 100000 Temperature (log) 10000 1000-10 Planetary Nebula Horizontal Branch Asymptotic Branch Helium Flash Kelvin-Helm holtz Contraction -5 Adjust to Main Sequence Sub Giant Core Contraction Hayashi Track 0 5 Absolute Magnitude White Dwarf 10 15 20
The Main Sequence and Very Large Stars Successive collapses and burnings Iron core Catastrophic collapse supernova the Death of Stars
Layers of Massive Star Layers H -> He He -> C C -> O of O -> Ne Nuclear Fusion in Ne -> Mg Mg -> Si High Mass Stars Fe Si -> Fe
Neutron Stars and Pulsars Neutron Star Dense and small High rotation rate Little light Pulsar Special neutron star Electromagnetic radiation End state of supernova
Black Holes Black Hole Result of collapse large star Nothing escapes from surface Cannot see them See impact on other stars Detect x-rays, gamma rays
iclicker Question It is estimated that the total lifetime of our Sun is 11 billion years. How far is it through its hydrogen-burning phase now? A 10% B 25% C 50% D 90%
iclicker Question Triangulation and Cepheid variable are methods to measure: A distances to stars B energy output of stars C lifetime of stars D composition of stars
iclicker Question A Hertzsprung-Russell diagram plots a star s temperature versus its: A energy output B distance C age
iclicker Question Large dust and gas clouds are commonly found throughout space. They are called: A red giants B galaxies C nebulae D supernovae E white dwarfs
iclicker Question The fusion process in very large stars produces chemical elements up to: A He B C C Fe D U E Pb
iclicker Question All natural elements beyond iron are created in: A supernova explosions B fusion of very large stars C the big bang
iclicker Question An object that is so dense and massive that nothing, including light can escape from its surface is called: A a supernova B a red giant C a white dwarf D a black hole E a neutron star
iclicker Question Are you surprised that the chemical elements about you were made in a supernova? A yes B no