Astronomy 113. Dr. Joseph E. Pesce, Ph.D. Review. Semester Recap. Nature of Light. Wavelength. Red/Blue Light 4/30/18

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1 3/10/ /melodysheeptime-lapse-universe-earthformation-watch Astronomy 113 Dr. Joseph E. Pesce, Ph.D. Review Semester Recap ³Light and Radiation ³The Sun ³Measuring Stars ³Gas Clouds ³Star Formation and Evolution ³End States of Stars ³Our Galaxy and other Galaxies ³Cosmology ³Life 20-2 ³Wave? Particle (photon)? ³Electromagnetic waves 20-3 Nature of Light ³Waves cycle in space 20-4 Wavelength 20-5 Red/Blue Light ³Red light has longer wavelength than blue ³Red light has a lower energy than blue ²Remember: Longer wavelengths = lower energy ³Wavelength: distance between crests or troughs 1

2 ³Radio ³Infrared ³Visible ³Ultraviolet ³Xrays ³Gamma-rays 20-6 The Electro-magnetic Spectrum Intensity 20-7 Blackbody Emission Wien s law Wavelength Stefan s law 20-8 Spectral Features 20-9 Bohr Atom Doppler Effect Transport of energy Radiative (= photons) + Convection Interior of Sun Random walk : g-ray to visible (Infrared) million yrs 2

3 In the sun: (600million tons of Hydrogen/sec = 170,000 yrs to consume mass of earth; in 10 billion years. 4 protons: (Hydrogen) + 2 electrons Fusion n p + p + p + p + p + e - e - + n p + 1 helium nucleus More mass before than after - mass conserved, so extra becomes energy (E=mc 2 ) in the form of a photon, the g-ray g-ray & neutrino ³Core/Interior ³Photosphere ³Chromosphere ³Corona Solar Structure ³Sunspots ³Flares ³Prominences ³Solar wind Activity on the Sun ³Parallax Distances to Stars Stellar Brightness ³Depends on distance and luminosity ²Inverse square law of light Magnitudes ³Apparent magnitude (m) ² Measured on Earth ³ Absolute magnitude (M) ² Apparent magnitude of a star if it were at 10pc from Earth ² Measure of absolute brightness or luminosity 3

4 Color Index ³Hot stars emit more blue light than cool stars ³Color Index is ratio of blue/red ³Color Index is related to surface temperature Spectral Types O B A F G K M ³Hot to cool ³Bright to faint ³Classified by spectra H-R Diagram Interstellar Medium ³Gas and dust between stars ³Reddens, polarizes, and blocks (extincts) light ³Emission nebula and HII regions ³HI gas ³Hot, warm, cold phases ³Giant Molecular Clouds Joseph E. Pesce, Ph.D. Hydrostatic Equilibrium ³ Hydrostatic Equilibrium ² Balance of force of gravity, which tries to squeeze Sun, and radiative pressure from fusion, which tries to blow apart Sun Star Formation

5 Low-mass Star Evolution The Evolution of a Low-Mass Star ³Post Main Sequence ³Core depletion of hydrogen ³Hydrogen shell burning ³Helium flash and helium core ³Helium depletion ³Helium shell ³Helium shell flashes ³Planetary nebula ³White dwarf High Mass Stars ³5-50 times the mass of the sun ²Last about 1 million years (very short!) ²Create elements through iron (fusion) ² Onion skin ²Expand into Red Supergiant ²Explode as a supernova ²Leave behind neutron stars or black holes Onion-skin nature of High Mass Stars Outer Atmosphere - Hydrogen Core - Fe Si Ag Ar Ne C He Not to scale Joseph E. Pesce, Ph.D. ³Type II Supernova ²Iron core cannot burn ²Mass exceeds Chandrasekhar limit ²Core collapses ²Core bounces ²Star destroyed ³ Type I ²White dwarf exceeds Chandrasekhar limit and explodes ³Nova Nova vs. Supernova ²Explosion on surface of white dwarf ²Luminosity = 10,000 x sun ²White dwarf survives explosion ³Supernova ²Star destroyed ²Luminosity = 100 billions x sun ²Neutron star or blackhole remains + remnant 5

6 Pulsars Our Galaxy ³Magnetized, rotating neutron star Halo Bulge Halo Disk Nucleus Rotation Curves Dark Matter ³Matter detected through its gravity ²Has no detectable electromagnetic emission ³Over 90% of the mass of the Galaxy is composed of this dark matter ³Plots of orbital velocity versus distance from nucleus ³Gives measure of mass WITHIN each orbit ³Found everywhere we can measure it s gravitational influence. Universe is full of it The Hubble Sequence (1920s) Types of Galaxies Stellar Populations in Galaxies ³Elliptical galaxies ²Population II stars ²Old, red ²Very low metal abundance ³Spiral galaxies ²Population I stars in spiral arms, Pop II in bulge & halo ²Young, blue stars ²Ongoing star formation in arms

7 Hubble s Law v r = H o * D Cepheid Period-Luminosity Relationship ³H o = Hubble Constant =? ²Need to measure z (easy) and D (hard) ²HST Key Project (observe Cepheids to 200Mly) ³More distant galaxies moving away faster ³Why? ³Universe is expanding (from an explosion ) Standard Candles ³Objects with known intrinsic luminosity ³Luminosity if the same wherever object is ³Luminosity is known fairly accurately ³Comparing absolute and apparent magnitudes gives distance ³Types ²Cepheids ²Supernovae (Type I) ²Red Giants ²Others Active Galaxies ³The centers of some galaxies are producing HUGE amounts of energy ²About 5% of galaxies ³These are ACTIVE GALAXIES, or ACTIVE GALACTIC NUCLEI (AGN) ³Non-thermal radiation ³Radio Galaxies ³Quasars ³BL Lacerta Objects ³Seyfert Galaxies Types of AGN What Powers an AGN? 7

8 The Cosmological Principle ³The universe is isotropic and homogenous ³We are not in a special location Implications of Hubble s Law ³Hubble s law must obey the Cosmological Principle ³Everything is expanding, everywhere ³If we go backwards in time, the universe must be getting ever smaller, denser, and hotter ²BIG BANG Cosmic Microwave Background Radiation ³Predicted by Big Bang Theory ³Fossil from early days of universe ³First observed by Penzias and Wilson, confirmed multiple times ³Excellent agreement between theory and observation Dark Matter & Fate of Universe ³Dark matter is important because it adds to mass of universe ³Mass of universe dictates how universe will end 1. Expand forever, at ever decreasing rate (open, unbound) 2. Expand forever at same speed (open, unbound) 3. Expansion stops eventually and universe collapses on itself (closed, bound) ³We appear to be in #1 state Dark Energy ³But this doesn t seem to matter much, because mass/energy dominated by dark energy ²Most mass is dark matter ²Most energy/mass is dark energy ³Causing expansion to accelerate The Universe ³Started in Big Bang, with Inflation ³Matter dominated universe filled with Dark Energy ³Matter froze out when Universe was s old ³All Hydrogen and some Helium (and a smattering of Li, Be, & B) formed in shortly after the Big Bang 8

9 ³Found everywhere in space ³Certainly fell on early Earth ³Life everywhere? Organic Molecules Solar System ³Earth is in habitable zone: ideal temperature and pressure for liquid water ³What about elsewhere? ²Mars had water in past under surface now ²Europa may have liquid water under surface ice Extrasolar Planets ³Everywhere we look (all types of stars) ³Every type of planet ²Gas giants ²Rocky earths Extraterrestrial Life ³ Lower forms (e.g., amoeba, bacteria, etc) ²Almost certainly ³Intelligent life (e.g., humans) ²Unknown, but maybe less likely ³Almost certainly no aliens visiting us now! Thank You! 9