This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Recap Galaxies Recap Galaxies Describe similarities and differences in the observation of a galaxy and of Crab Nebula Describe our galaxy (the Milky Way) What type of observation was most important in establishing the type of our galaxy ? What types of galaxies are in the Universe and which type is most abundant ? Is there a link between various type of galaxies ? Discuss the types of active galaxies and the possible link between these types. The Creation of the Universe The Creation of the Universe The Universal Expansion Big Bang or Continuous Creation ? The Temperature of the Universe The First Fractions of a Second Where is the Antimatter ? After the First Second The Universal Expansion The Universal Expansion Cosmogony – the early biography of the Universe (the “archeology” of the Universe) V.Slipher (1912) and E.Hubble(1923) showed the most galaxies have the atomic spectra shifted towards red. 1929 Hubble and Humason established that this shift increases with the galaxies becoming dimmer and dimmer. Hubble plotted galaxies speed vs distance and that plot bears his name. Galactic distances were calculated with Cepheid stars measurements. Big Bang or Continuous Big Bang or Continuous Creation ? 1922 A.Friedman showed that Einstein’s general relativity equations can have a solution corresponding to an expanding or contracting Universe. 1926 Hubble’s diagram showed that all galaxies started from the same point. Unfortunately, Hubble obtained a life of the Universe shorter than the age of Earth (as found in the studies of rocks and fossils) H.Bondi, T.Gold and F.Hoyle proposed a Continuous Creation (or a Stationary State) model of the Universe, which uses intergalactic white holes. 1952 W.Baade at Palomar discovers the error in Hubble’s observations and makes the Universe older than Earth. 1951 the Vatican officially supports the Big Bang model. 1950s G.Gamow, R.Alpher and R.Hermann determine the production of elements during the first moments of the Big Bang. Hoyle’s model continued to be a direct competitor of Big Bang. But in 1965 another discovery eliminated completely Hoyle’s Continuum Creation. The Temperature of the Universe The Temperature of the Universe In 1965 Bell Labs announced that the Universe contains a radio energy corresponding to a temperature of 3 Kelvin degrees (or –270 degrees Celsius). That agreed well with the Big Bang model. “Accidents” at Bell Labs: 1931 K.Jansky did the first radioastronomical observations 1965 A.Penzias and R.Wilson discovered the cosmic microwave radiation. R.Dicke at Princeton was able to repeat the experiment of Penzias and Wilson and that marked the publication of the result known to physicists as “the Universal 3oK black body radiation”. The First Fraction of a Second The First Fraction of a Second (I) Big Bang was the most powerful phenomenon imaginable. At less than 1035 seconds from the beginning of the Big Bang and at temperatures above 1028 degrees the 10 dimensional Universe had a democracy of particles (squeezed at distances smaller than 1033 cm) and forces. At a slightly lower temperature a symmetry breaking created an abundance of superheavy Higgs bosons, which gave the weight (1015 GeV) to the hyperweak force carriers. The hyperweak force transformed baryons into leptons and antibaryons into antileptons. The First Fraction of a Second (II) The First Fraction of a Second (II) The asymmetry in the hyperweak transformations makes the disintegration of antibaryons more probable. This created a Universe dominated by particles over antiparticles. More exactly it created the observed ratio of 1 antihadron to 10,000 hadrons. It also created the observed ratio of 1 baryon to 1 billion photons. This period has a huge predominance of radiation (photons at energies of MeV) over matter (baryons at energies of GeV) . Today while the ratio is preserved, the photons have energies of order of 103 eV and that change makes matter more important than radiation. How to measure these ratios ? One can weigh a galaxy from its dynamics and one can measure its size. The result is an average density of about 106 – 108 baryons per cubic cm. The density of photons is found by physicists to be about 400 photons per cubic cm. It is remarkable that the same ratio of baryons/photons is obtained from a model of Big Bang at temperatures above 1012 degrees. The First Fraction of a Second (III) The First Fraction of a Second (III) After 104 seconds from beginning of the Big Bang the Universe reached a temperature of 1012 degrees. At about 103 seconds from the beginning of the Big Bang, after the breaking of symmetry occurring when particles were at distances of around 1016 cm, the fundamental forces were functioning like today. In this state theorists believe that small fluctuations were amplified and lead to the formation of galaxies. Recent calculations show that a model with 6 types of quarks leads to a “soup of hadrons” capable to produce galaxies. Between 104 and 103 seconds at a temperature of 1011 degrees most heavy baryons disintegrated creating protons and neutrons and a large number of neutrinos, while the radiation created pairs of electrons and positrons. The Inflationary Model (I) The Inflationary Model (I)
The Grand Unified Theories - based Inflationary Model predicts a 50 orders of magnitude increase for the 10-32 seconds old Universe. 1 10-10 size (cm)
10-50 10-60 10-35 10-25 10-15 time (sec) The Inflationary Model (II) The Inflationary Model (II) How is the inflation possible ? Vacuum is a “bubbling” environment based on quantum fluctuations of massenergy. Alan Guth has shown that it is possible to buildup these quantum “kicks” to create “galactic seeds”. Guth showed that for the Universe to be the way it is the inflation doubling its size 100,000 times should have stopped after 1030 seconds (the inflation energy had to decay). After the First Second (I) After the First Second (I) S.Weinberg “The First Three Minutes” At 10 billion degrees the neutrinos decoupled from the rest of particles and the weak force stopped from changing protons and neutrons: their ratio froze to a value 1/61/7. At 3 billion degrees the radiation was unable to create pairs of electrons/positrons and the density of photons became a constant (like that of neutrinos) At 1 billion degrees the fusion of protons started. It formed deuterons and then helium nuclei. In only 200 seconds this process changed about a quarter of protons into helium nuclei. Today’s observed ratio of helium to hydrogen is 3/10, with the extra 5% increase being due to the fusion reactions inside the stars. The total number of baryons observed today in stars and intergalactic is related to the number of particles which were produced during the Big Bang and this link established that the number of quarks can be either 6 or maximum 8. After the First Second (II) After the First Second (II) The cooling of the Universe happened in a few hundreds of thousands of years. At 5000 degrees (the temperature at the surface of our Sun), the radiation was separated from heavy matter and the cooling continued separately for the heavy matter, for photons and for neutrinos. The cooling of the photons lead in time to the microwave radiation observed by Penzias and Wilson. Zeldovich and his collaborators determined that the temperature of the neutrinos should be today around 2 absolute degrees (still undetectable) The first atoms were formed about 300,000 years from the beginning of the Big Bang, when the Universe was about 20,000 smaller than today. Galaxies Formation Galaxies Formation The first galaxies were formed when the Universe was about 100 million years old having a density about 10,000 larger than today. A possible scenario considers primordial black holes as the seeds for their formation (it is also possible that simple clouds of matter separated during the expansion). Young galaxies are associated with quasars and the fact that the most remote quasars correspond to an age of the Universe of about 1 billion years indicates that the galaxies before that time were too small or dim to be seen today. The first stars inside galaxies were probably formed in parallel to their activity as quasars. Our solar system corresponds to 2nd or 3rd generation of stars which use a large concentration of heavy elements produced in supernovas. The separation of galaxies of different sizes would create a non uniform Universe, in contradiction with the current galactic observations. A.Guth’ inflationary model provides the explanation for a uniform distribution of the clusters of galaxies. ...
View Full Document
This note was uploaded on 05/03/2011 for the course NATS 1740 taught by Professor Hall during the Spring '10 term at York University.
- Spring '10