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The Electromagnetic Spectrum

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The Electromagnetic Spectrum Cosmology The Electromagnetic Spectrum Wavelength (m) Frequency (Hz) Energy (J) Radio > 1·10−1 < 3·109 < 2·10−24 Microwave 1·10−3 - 1·10−1 3·109 - 3·1011 2·10−24 - 2·10−22 Infrared 7·10−7 - 1·10−3 3·1011 - 4·1014 2·10−22 - 3·10−19 Optical 4·10−7 - 7·10−7 4·1014 - 7.5·1014 3·10−19 - 5·10−19 UV 1 ·10−8 - 4·10−7 7.5·1014 - 3·1016 5·10−19 - 2·10−17 X-ray 1·10−11 - 1·10−8 3·1016 - 3·1019 2·10−17 - 2·10−14 Gamma-ray < 1·10−11 > 3·1019 > 2·10−14 See also: RoRo c 2009, F. Jegerlehner nx Lect. 2 xo 38 Cosmology c 2009, F. Jegerlehner nx Lect. 2 xo 39 Cosmology « balloon, satellite, space station experiments, space telescopes Sun light: Fraunhofer lines 1814; Kirchhoff, Bunsen Spectral Analysis ∼ 1850 The birth of astrophysics: first astrophysics institute at Potsdam 1874, in 1910 Schwarzschild became the director, enthusiastically participated world war I, came back gas poised ill. He found the famous Schwarzschild solution (black-hole) only a few weeks after Einstein’s 1916 GRT paper, shortly before he passed away. Observation of Atomic Spectra quite some time later lead to the development of Quantum Mechanics and c 2009, F. Jegerlehner nx Lect. 2 xo 40 Cosmology the precise theory of atomic spectra finally explained such observation: q Atoms show typical a emission spectrum of discrete lines as prescribed by quan- tum mechanics and atomic theory. c 2009, F. Jegerlehner nx Lect. 2 xo 41 Cosmology q Stars like the Sun radiate a continuous spectrum, due to a wealth of simultane- ous atomic and nuclear processes taking place under extreme conditions. q Continuous spectrum light passing trough a gas absorbs those frequencies which fit with the atomic spectral excitations possible. The resulting absorption spectrum allow us to identify the chemical composition of the gas or the stars atmosphere. The missing lines seen in the Fraunhofer spectrum of the Sun tell us the composition of the Sun’s atmosphere. c 2009, F. Jegerlehner nx Lect. 2 xo 42 Cosmology Doppler Effect One of the key phenomena in astronomy and cosmology is the Doppler Effect Light emitted by moving light sources is red shifted if the source is departing from the observer or blue shifted if the source is approaching the observer. c 2009, F. Jegerlehner nx Lect. 2 xo 43 Cosmology The quantitative description will be given below. See also: Ro c 2009, F. Jegerlehner nx Lect. 2 xo 44 Cosmology Distance Ladder, Measuring Distances This is a synopsis of most of the distance measuring methods: Ê For the Solar System: Radar is the most accurate measuring method. c 2009, F. Jegerlehner nx Lect. 2 xo 45 Cosmology Ë For nearby stars: The parallax method, using either Earth’s orbit to occupy different positions or an orbiting satellite, to determine how far away are stars in the Milky Way Galaxy; works well out to about 3000 light years. For some stars farther out in the Milky Way: The standard candle method uses stars whose true luminosity L can be determined. Í For stars out to the edge of the Milky Way: The Cepheid Variable star method is employed. Î For many more distant galaxies out to several hundred million light years: The Tully-Fisher method utilizes measured brightness and galaxy rotation (using the Doppler effect). Ï For galaxies out to about 10 billion light years: This depends on observations of White Dwarf supernovae, whose intrinsic brightness is well known. Some of these methods have accuracies of +/- 10% or better. c 2009, F. Jegerlehner nx Lect. 2 xo 46 Cosmology c 2009, F. Jegerlehner nx Lect. 2 xo 47 Cosmology For the foundation of the Extragalactic Distance Scale Cepheid pulsating variable stars played a key role. The relationship between a Cepheid variable’s luminosity and pulsation period is quite precise, securing Cepheids as viable standard candles. In 1784 Edward Pigott detected the variability of Eta Aquilae. c 2009, F. Jegerlehner nx Lect. 2 xo 48 Cosmology c 2009, F. Jegerlehner nx Lect. 2 xo 49 Cosmology See: Ro c 2009, F. Jegerlehner nx Lect. 2 xo 50 Cosmology v large hot stars, masses 5-20 ×M , up to 30000 ×L v pulsate with periods of a few days to months v two classes: Population I and II v radii change by several million kilometers (30%) in the process v HST has seen Cepheids out to a distance of some 100 million light years Over 700 classical Cepheids are known in the Milky Way galaxy several thousand within the Local Group of galaxies. A few more have been identified outside the Local Group. c 2009, F. Jegerlehner nx Lect. 2 xo 51 Cosmology Our place in the cosmos: Earth Moon 1.3 light-seconds (380’000 km) Sun 8 light-minutes (150’000’000 km) Nearest Stars 4 light-years Center of Galaxy 30’000 light-years Andromeda Nebula 2 million light-years Quasar 3C 273 2 billion light-years Farest Star 13 billion light-years GRB 090423 Farest Galaxy 13.23 billion light-years ESO 2004, red shift 10 The farest object identified, the Abell 1835 / IR1916 galaxy, is seen at a time when the Universe was merely 470 million years young, that is, barely 3 percent of its current age. The farther we look out in space the younger the objects seen, i.e., we are looking back in time (see this: Ro). List of most distant objects see: Ro c 2009, F. Jegerlehner nx Lect. 2 xo 52 Cosmology discovered April 23, 2009, first seen in γ-rays, light from 630 Million years after B.B. Giant star exploding: GRB 090423 13 Billion light-years away c 2009, F. Jegerlehner nx Lect. 2 xo 53 Cosmology Setting Up the Scene As mentioned before, the basis for cosmology is given by a wealth of observational data as well as theoretical models. Thereby, particle, atomic and nuclear physics and thermodynamics as well as solid state physics and astrophysics play an equally important role. Most important star data are v Distance v Size – Mass v Color – Temperature v Spectra – Chemical Composition Stars and systems of stars have a specific well understood evolution history. It is possible to determine the age of stars and galaxies and to explain the origin of the chemical elements. c 2009, F. Jegerlehner nx Lect. 2 xo 54 Cosmology All this follows from sophisticated investigations of the finest details of the electromagnetic spectrum, thereby radio sources like pulsars (discovered 1967) yield very important information. The variety of stars of different sizes, the evolution of stars, the classification of stars teaches us many details of understanding. An impressive example is the Hertzsprung-Russell diagram c 2009, F. Jegerlehner nx Lect. 2 xo 55 Cosmology c 2009, F. Jegerlehner nx Lect. 2 xo 56 Cosmology On the small scale of distances (nearby zone) matter is accumulated in r Stars 1 ly r Galaxies 106 lys 106 ÷ 1012 stars r Clusters of Galaxies 3·107 lys 50 to 1000 galaxies What is called near-zone in cosmology/astronomy is somewhat arbitrarily set by 1 Gpc (Giga parsecs) [1 pc ' 3.262 ly ' 3.085678 ×1016 m] ≡ earth 1 parsec (pc) distance at which the mean r =^ 1AU distance earth-sun is seen as 1 arcsecond 100 sun (mean distance earth-sun ∼ radius of earth orbit = 1 AU (astronomical unit)) 1 parsec Group of galaxies: local group about 40 Galaxies part of Virgo cluster about 1300 galaxies discovered in 1770’s (Messier et al.) c 2009, F. Jegerlehner nx Lect. 2 xo 57 Cosmology Group of Galaxies: HCG 87, 400·106 light-years away c 2009, F. Jegerlehner nx Lect. 2 xo 58 Cosmology Virgo Cluster: 60·106 light-years away c 2009, F. Jegerlehner nx Lect. 2 xo 59 Cosmology Farest known Cluster: JKCS041, 10·109 light-years away c 2009, F. Jegerlehner nx Lect. 2 xo 60 Cosmology It (1 Gpc) is the practical limit for neglecting v Curvature of Space p 2 2 v Relativistic Effects [3 expansion velocity 1 − 3 =c ∼>0:96 ∼ 1] v Time-Evolution [expansion effects negligible: ! snapshot] Note: 1 Gpc ' 3:26 · 109 years 12 · 109 years Before we will continue with looking at the universe at cosmological distances let us sketch stellar evolution to learn more about the objects which make up the galaxies and which are the primary sources of the signals we have to decode. c 2009, F. Jegerlehner nx Lect. 2 xo 61 Cosmology Stellar Evolution Stars are formed from large clouds of interstellar dust and hydrogen gas left over from the creation of the Universe. Disturbances in the clouds cause a clumping of the gas and dust which then pulls more matter in due to gravity. The particles of dust and gas will rub against each other, and heat up due to friction. They will also begin to rotate around the center of the clump. The rotating center of the clump of gas and dust is called a ’protostar’ (Search for it: new infrared telescope Herschel seraching for “cold” places in space: Ro ). c 2009, F. Jegerlehner nx Lect. 2 xo 62 Cosmology Orion Nebula: birth place of stars c 2009, F. Jegerlehner nx Lect. 2 xo 63 Cosmology A cloud of gas and dust called RCW120 as seen by Herschel. The large blue bubble is being blown out by a massive star (unseen) in the centre. This creates the conditions for a giant young star to form on the bubble’s bottom edge (white blob) [source ESA/BBC] c 2009, F.
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