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: -≫-≫
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 38 Cosmology
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 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 ≪R Lect. 2 R≫ 40 Cosmology the precise theory of atomic spectra finally explained such observation:
K Atoms show typical a emission spectrum of discrete lines as prescribed by quan- tum mechanics and atomic theory.
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 41 Cosmology
K Stars like the Sun radiate a continuous spectrum, due to a wealth of simultane- ous atomic and nuclear processes taking place under extreme conditions.
K 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 ≪R Lect. 2 R≫ 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 ≪R Lect. 2 R≫ 43 Cosmology
The quantitative description will be given below. See also: -≫
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 44 Cosmology Distance Ladder, Measuring Distances
This is a synopsis of most of the distance measuring methods:
For the Solar System: Radar is the most accurate measuring method.
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 45 Cosmology
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.
For stars out to the edge of the Milky Way: The Cepheid Variable star method is employed.
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).
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 ≪R Lect. 2 R≫ 46 Cosmology
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 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 ≪R Lect. 2 R≫ 48 Cosmology
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 49 Cosmology
See: -≫
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 50 Cosmology
O large hot stars, masses 5-20 ×M , up to 30000 ×L
O pulsate with periods of a few days to months
O two classes: Population I and II
O radii change by several million kilometers (30%) in the process
O 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 ≪R Lect. 2 R≫ 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: -≫).
List of most distant objects see: -≫
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 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 ≪R Lect. 2 R≫ 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
O Distance O Size – Mass O Color – Temperature O 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 ≪R Lect. 2 R≫ 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 ≪R Lect. 2 R≫ 55 Cosmology
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 56 Cosmology
On the small scale of distances (nearby zone) matter is accumulated in Ì Stars 1 ly Ì Galaxies 106 lys 106 ÷ 1012 stars Ì 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 =ˆ 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 ≪R Lect. 2 R≫ 57 Cosmology
Group of Galaxies: HCG 87, 400·106 light-years away
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Virgo Cluster: 60·106 light-years away
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Farest known Cluster: JKCS041, 10·109 light-years away
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 60 Cosmology
It (1 Gpc) is the practical limit for neglecting
O Curvature of Space
p 2 2 O Relativistic Effects [3 expansion velocity 1 − 3 /c ∼>0.96 ∼ 1] O 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 ≪R Lect. 2 R≫ 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: -≫ ).
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 62 Cosmology
Orion Nebula: birth place of stars
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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. Jegerlehner ≪R Lect. 2 R≫ 64 Cosmology
Carina Nebula (NGC 3372) a star breeding factory c 2009, F. Jegerlehner ≪R Lect. 2 R≫ Credit: HST/NASA/ESA 65 Cosmology
Read: -≫, zoom: -≫
As more of the matter falls into the center, the protostar continues to heat up. If it reaches a critical temperature (about 10,000,000 C), nuclear fusion will begin in its core. Hydrogen atoms fuse to form helium. This provides all of the star’s energy, which is given out as heat and light. A star that is ’burning’ hydrogen in a nuclear reaction is known as a Main Sequence star. It will spend most of its lifetime like this.
The hydrogen in the star’s central region or ’core’ will eventually run out and the star will then expand to become a red giant (see -≫). When this happens to the Sun it will expand out to a distance of the Earth’s orbit. If the star is hot enough in the center, it will begin a new fusion reaction, turning helium into the heavier element carbon.
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 66 Cosmology
Red Giant
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 67 Cosmology
Solar-type stars
At this point, the star’s evolution depends on its mass. A low mass star like our Sun will stop fusion reactions as soon as the helium has run out. When this happens the core of the star will contract. This throws off the outer layers of the star to form an expanding shell of glowing dust and gas called a ’planetary nebula’.
The star that is left in the center is known as a ’white dwarf’. At this point the star is about the same size as the Earth, but it is incredibly dense. A sugar-cube sized piece of the star would weight as much as two fully-grown polar bears. The white dwarf starts at a temperature of about 10,000 C but will eventually cool and fade until it can no longer be seen. It is then known as a ’black dwarf’. It will stay like this forever.
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 68 Cosmology
Planetary Nebula NGC 6302
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 69 Cosmology
Massive stars
A star more massive than the Sun will be hot enough in the center for further fusion reactions to begin, so will continue to burn carbon into oxygen, and oxygen into silicon and so on, until either the star is not hot enough to start another reaction or iron is created. Once the fuseable elements run out, the star will collapse and explode in a supernova (see -≫ ). This leaves behind a very dense core called a ’neutron star’. This is even more dense than a white dwarf. A cubic centimeter of neutron star would weigh as much as all of the people on the Earth put together that’s 6 billion people packed into a volume the size of a sugar cube!
Super Nova
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 70 Cosmology
Very massive stars
An even more massive star, one more than 25 times the mass of the Sun, would collapse even further to form a black hole.
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 71 Cosmology
Black-Hole
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 72 Cosmology
This black hole located in the Centaurus galaxy illustrates their gravitational pull: the jet of material flowing into the center is 13,000 light years long and is traveling at half the speed of light. This image is a fusion of visible light and x-ray radiation data.
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 73 Cosmology b.Luminosity Abs. Hertzsprung-Russell-Diagram
Red Giant
pulsation nucleus contraction shell expansion contraction nuclear Sun reactions Main Sequence Protostar
White Dwarf Temterature ←
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 74 Cosmology Neutrino Physics meets Astrophysics Note: solar neutrino experiments and the solution of the solar neutrino problem have for the first time confirmed our precise understanding of the theory of the sun (Solar Standard Model J. Bahcall et al.). Neutrino experiments in particular SNO (Sudbury Neutrino Observatory) have confirmed that we precisely understand the physics of energy production of the sun. Nuclear fuel of the sun:
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 75 Cosmology
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 76 Cosmology
SNO (in Canada) was able to measure separately the different neutrino fluxes from different reactions in sun’s energy production, and fully confirmed the solar SM of Bahcall.
We now know for sure how the sun shines!
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 77 Cosmology
See Bahcall’s article: -≫
What SNO has been doing?
Transparencies from A. McDonald, SNO Collab., Nobel Symposium, Stockholm 2004
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 78 Cosmology
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Milestone not only for Neutrino Physics, equally important for Astrophysics!
Establishes detailed understanding for energy production of stars like the sun.
Observed neutrino deficit is due to flavor transitions νe ↔ νµ ↔ ντ called Neutrino Oscillations! i.e. νe’s produced in sun transform into νµ’s and ντ’s and thus that portion is missing when we look for νe’s only.
2002 Nobel Prize in Physics to R. Davis and M. Koshiba ”for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos [Homestake and Kamiokande/Super-Kamiokande experiments]”.
c 2009, F. Jegerlehner ≪R Lect. 2 R≫ 86 Cosmology
For the elementary particle physics SNO (in Canada) together with SUPER-KAMIOKANDE (in Japan) prove that neutrinos are mixing (νe ↔ νµ ↔ ντ), which is possible only if they have non-vanishing masses which in addition must differ from each other (mνe , mνµ , mµτ). 2015 Nobel Prize in Physics to T. Kajita and A. McDonald ”for the discovery of neutrino oscillations, which shows that neutrinos have mass”.
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