Hubble's Cosmology
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Olbers' Paradox
Astro 101 Fall 2013 Lecture 12 Cosmology T. Howard Cosmology = study of the Universe as a whole • ? What is it like overall? • ? What is its history? How old is it? • ? What is its future? • ? How do we find these things out from what we can observe? • In 1996, researchers at the Space Telescope Science Institute used the Hubble to make a very long exposure of a patch of seemingly empty sky. Q: What did they find? A: Galaxies “as far as The eye can see …” (nearly everything in this photo is a galaxy!) 40 hour exposure What do we know already (about the Universe) ? • Galaxies in groups; clusters; superclusters • Nearby universe has “filament” and void type of structure • More distant objects are receding from us (light is redshifted) • Hubble’s Law: V = H0 x D (Hubble's Law) Structure in the Universe What is the largest kind of structure in the universe? The ~100-Mpc filaments, shells and voids? On larger scales, things look more uniform. 600 Mpc Olbers’ Paradox • Assume the universe is homogeneous, isotropic, infinte, and static • Then: Why don’t we see light everywhere? Why is the night sky (mostly) dark? Olbers’ Paradox (cont’d.) • We believe the universe is homogeneous and isotropic • So, either it isn’t infinite OR it isn’t static • “Big Bang” theory – universe started expanding a finite time ago Given what we know of structure in the universe, assume: The Cosmological Principle On the largest scales, the universe is roughly homogeneous (same at all places) and isotropic (same in all directions). Laws of physics are everywhere the same. -
Friedmann Equation (1.39) for a Radiation Dominated Universe Will Thus Be (From Ada ∝ Dt)
Lecture 2 The quest for the origin of the elements The quest for the origins of the elements, C. Bertulani, RISP, 2016 1 Reading2.1 - material Geometry of the Universe 2-dimensional analogy: Surface of a sphere. The surface is finite, but has no edge. For a creature living on the sphere, having no sense of the third dimension, there is no center (on the sphere). All points are equal. Any point on the surface can be defined as the center of a coordinate system. But, how can a 2-D creature investigate the geometry of the sphere? Answer: Measure curvature of its space. Flat surface (zero curvature, k = 0) Closed surface Open surface (posiDve curvature, k = 1) (negave curvature, k = -1) The quest for the origins of the elements, C. Bertulani, RISP, 2016 2 ReadingGeometry material of the Universe These are the three possible geometries of the Universe: closed, open and flat, corresponding to a density parameter Ωm = ρ/ρcrit which is greater than, less than or equal to 1. The relation to the curvature parameter is given by Eq. (1.58). The closed universe is of finite size. Traveling far enough in one direction will lead back to one's starting point. The open and flat universes are infinite and traveling in a constant direction will never lead to the same point. The quest for the origins of the elements, C. Bertulani, RISP, 2016 3 2.2 - Static Universe 2 2 The static Universe requires a = a0 = constant and thus d a/dt = da/dt = 0. From Eq. -
Throughout the Universe, Galaxies Are Rushing Away from Us – and from Each Other – at Tremendously High Speeds
Our Universe Began with a Bang Throughout the Universe, galaxies are rushing away from us – and from each other – at tremendously high speeds. This fact tells us that the Universe is expanding over time. Edwin Hubble (after whom the Hubble Space Telescope was named) first measured the expansion in 1929. Observatories of the Carnegie Institution of Washington Edwin Hubble This posed a big question. If we could run the cosmic movie backward in time, would everything in the Universe be crammed together in a blazing fireball – the starting point of Edwin Hubble & Proceedings of The National Academy of Sciences Hubble’s famous diagram showing the the Big Bang? A lot of scientific distance versus velocity of the galaxies he debate and many new theories observed. The farther away the galaxies, the faster they are moving, showing that the followed Hubble’s discovery. Universe is expanding. Among those in the front lines of the debate were physicists Ralph Alpher and Robert Herman. In 1948 they predicted that an afterglow of this fireball should still exist, though at a much lower temperature than at the time of the Big Bang. Here’s why: As the Universe Fun Fact: expands, the waves of heat About radiation from the Big Bang are 1% of the stretched out, and cool from “snow” you see visible energy to infrared and on broadcast TV then to microwave wavelengths. is caused by the Microwaves are just short- cosmic microwave wavelength radio waves, the same background. form of energy used in microwave ovens. The prediction of an afterglow could be tested! Scientists began building instruments to detect this “cosmic microwave background”, or CMB. -
A New Universe to Discover: a Guide to Careers in Astronomy
A New Universe to Discover A Guide to Careers in Astronomy Published by The American Astronomical Society What are Astronomy and Astrophysics? Ever since Galileo first turned his new-fangled one-inch “spyglass” on the moon in 1609, the popular image of the astronomer has been someone who peers through a telescope at the night sky. But astronomers virtually never put eye to lens these days. The main source of astronomical data is still photons (particles of light) from space, but the tools used to gather and analyze them are now so sophisticated that it’s no longer necessary (or even possible, in most cases) for a human eye to look through them. But for all the high-tech gadgetry, the 21st-Century astronomer is still trying to answer the same fundamental questions that puzzled Galileo: How does the universe work, and where did it come from? Webster’s dictionary defines “astronomy” as “the science that deals with the material universe beyond the earth’s atmosphere.” This definition is broad enough to include great theoretical physicists like Isaac Newton, Albert Einstein, and Stephen Hawking as well as astronomers like Copernicus, Johanes Kepler, Fred Hoyle, Edwin Hubble, Carl Sagan, Vera Rubin, and Margaret Burbidge. In fact, the words “astronomy” and “astrophysics” are pretty much interchangeable these days. Whatever you call them, astronomers seek the answers to many fascinating and fundamental questions. Among them: *Is there life beyond earth? *How did the sun and the planets form? *How old are the stars? *What exactly are dark matter and dark energy? *How did the Universe begin, and how will it end? Astronomy is a physical (non-biological) science, like physics and chemistry. -
The High Redshift Universe: Galaxies and the Intergalactic Medium
The High Redshift Universe: Galaxies and the Intergalactic Medium Koki Kakiichi M¨unchen2016 The High Redshift Universe: Galaxies and the Intergalactic Medium Koki Kakiichi Dissertation an der Fakult¨atf¨urPhysik der Ludwig{Maximilians{Universit¨at M¨unchen vorgelegt von Koki Kakiichi aus Komono, Mie, Japan M¨unchen, den 15 Juni 2016 Erstgutachter: Prof. Dr. Simon White Zweitgutachter: Prof. Dr. Jochen Weller Tag der m¨undlichen Pr¨ufung:Juli 2016 Contents Summary xiii 1 Extragalactic Astrophysics and Cosmology 1 1.1 Prologue . 1 1.2 Briefly Story about Reionization . 3 1.3 Foundation of Observational Cosmology . 3 1.4 Hierarchical Structure Formation . 5 1.5 Cosmological probes . 8 1.5.1 H0 measurement and the extragalactic distance scale . 8 1.5.2 Cosmic Microwave Background (CMB) . 10 1.5.3 Large-Scale Structure: galaxy surveys and Lyα forests . 11 1.6 Astrophysics of Galaxies and the IGM . 13 1.6.1 Physical processes in galaxies . 14 1.6.2 Physical processes in the IGM . 17 1.6.3 Radiation Hydrodynamics of Galaxies and the IGM . 20 1.7 Bridging theory and observations . 23 1.8 Observations of the High-Redshift Universe . 23 1.8.1 General demographics of galaxies . 23 1.8.2 Lyman-break galaxies, Lyα emitters, Lyα emitting galaxies . 26 1.8.3 Luminosity functions of LBGs and LAEs . 26 1.8.4 Lyα emission and absorption in LBGs: the physical state of high-z star forming galaxies . 27 1.8.5 Clustering properties of LBGs and LAEs: host dark matter haloes and galaxy environment . 30 1.8.6 Circum-/intergalactic gas environment of LBGs and LAEs . -
Is the Universe Really Expanding?
Is the Universe really expanding? J.G. Hartnett School of Physics, the University of Western Australia 35 Stirling Hwy, Crawley 6009 WA Australia; [email protected] (Dated: November 22, 2011) The Hubble law, determined from the distance modulii and redshifts of galaxies, for the past 80 years, has been used as strong evidence for an expanding universe. This claim is reviewed in light of the claimed lack of necessary evidence for time dilation in quasar and gamma-ray burst luminosity variations and other lines of evidence. It is concluded that the observations could be used to describe either a static universe (where the Hubble law results from some as-yet-unknown mechanism) or an expanding universe described by the standard Λ cold dark matter model. In the latter case, size evolution of galaxies is necessary for agreement with observations. Yet the simple non-expanding Euclidean universe fits most data with the least number of assumptions. From this review it is apparent that there are still many unanswered questions in cosmology and the title question of this paper is still far from being answered. Keywords: expanding universe, static universe, time dilation I. INTRODUCTION eral relativity, which has been successfully empirically tested in the solar system by numerous tests [74], and with pulsar/neutron star and pulsar/pulsar binary pairs Ever since the late 1920’s, when Edwin Hubble discov- [16, 45, 62] in the Galaxy, is a very strong point in its fa- ered a simple proportionality [40] between the redshifts vor, and strong evidence for an expanding universe [69]. -
Einstein's Role in the Creation of Relativistic Cosmology
EINSTEIN'S ROLE IN THE CREATION OF RELATIVISTIC COSMOLOGY CHRISTOPHER SMEENK 1. Introduction Einstein's paper, \Cosmological Considerations in the General Theory of Relativ- ity" (Einstein 1917b), is rightly regarded as the first step in modern theoretical cosmology. Perhaps the most striking novelty introduced by Einstein was the very idea of a cosmological model, an exact solution to his new gravitational field equations that gives a global description of the universe in its entirety. Einstein's paper inspired a small group of theorists to study cosmological models using his new gravitational theory, and the ideas developed during these early days have been a crucial part of cosmology ever since. We will see below that understanding the physical properties of these models and their possible connections to astro- nomical observations was the central problem facing relativistic cosmology in the 20s. By the early 30s, there was widespread consensus that a class of models de- scribing the expanding universe was in at least rough agreement with astronomical observations. But this achievement was certainly not what Einstein had in mind in introducing the first cosmological model. Einstein's seminal paper was not simply a straightforward application of his new theory to an area where one would ex- pect the greatest differences from Newtonian theory. Instead, Einstein's foray into cosmology was a final attempt to guarantee that a version of \Mach's principle" holds. The Machian idea that inertia is due only to matter shaped Einstein's work on a new theory of gravity, but he soon realized that this might not hold in his “final” theory of November 1915. -
Appendix a the Return of a Static Universe and the End of Cosmology
Appendix A The Return of a Static Universe and the End of Cosmology Lawrence M. Krauss and Robert J. Scherrer Abstract We demonstrate that as we extrapolate the current CDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our “island universe” will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented. Shortly after Einstein’s development of general relativity, the Dutch astronomer Willem de Sitter proposed a static model of the universe containing no matter, which he thought might be a reasonable approximation to our low-density uni- verse. One can define a coordinate system in which the de Sitter metric takes a static form by defining de Sitter spacetime with a cosmological constant ƒ S W A B D 2 2 D 1 as a four-dimensional hyperboloid ƒ AB R ;R 3ƒ em- 2 D A B D bedded in a 5d Minkowski spacetime with ds AB d d ; and .AB / diag.1; 1; 1; 1; 1/;A;B D 0;:::;4: The static form of the de Sitter metric is then dr2 ds2 D .1 r2=R2/dt 2 s r2d2; s s s 2 2 s 1 rs =R L.M. -
Edwin Hubble (1889-1953) Measured Distance to Andromeda Galaxy (M31) • Noticed Individual Bright Stars in Andromeda
The Resolution: Edwin Hubble (1889-1953) Measured Distance to Andromeda Galaxy (M31) • Noticed individual bright stars in Andromeda • Calculated the distance using the Period-Luminosity Relation for Cepheid Variable Stars The Resolution: Edwin Hubble (1889-1953) Measured Distance to Andromeda Galaxy (M31) • Noticed individual bright stars in Andromeda • Calculated the distance using the Period-Luminosity Relation for Cepheid Variable Stars 1. MEASURED magnitude & Period The Resolution: Edwin Hubble (1889-1953) Measured Distance to Andromeda Galaxy (M31) • Noticed individual bright stars in Andromeda • Calculated the distance using the Period-Luminosity Relation for Cepheid Variable Stars 1. MEASURED magnitude & Period 2. CALCULATED Luminosity The Resolution: Edwin Hubble (1889-1953) Measured Distance to Andromeda Galaxy (M31) • Noticed individual bright stars in Andromeda • Calculated the distance using the Period-Luminosity Relation for Cepheid Variable Stars 1. MEASURED magnitude & Period 2. CALCULATED Luminosity 3. CALCULATED Distance The Resolution: Edwin Hubble (1889-1953) Measured Distance to Andromeda Galaxy (M31) • Noticed individual bright stars in Andromeda • Calculated the distance using the Period-Luminosity Relation for Cepheid Variable Stars 1. MEASURED magnitude & Period 2. CALCULATED Luminosity 3. CALCULATED Distance • Result was MUCH farther than expected... • (2.3 Million Ly - well beyond Milky Way) Henrietta Leavitt & Period-Luminosity Relation Cepheid Variables: Bright stars whose Luminosity (energy output) varies every -
Common Misconceptions of Cosmological Horizons and the Superluminal Expansion of the Universe
CSIRO PUBLISHING www.publish.csiro.au/journals/pasa Publications of the Astronomical Society of Australia, 2004, 21, 97–109 Expanding Confusion: Common Misconceptions of Cosmological Horizons and the Superluminal Expansion of the Universe Tamara M. Davis and Charles H. Lineweaver University of New South Wales, Sydney NSW 2052, Australia (e-mail: [email protected]; [email protected]) Received 2003 June 3, accepted 2003 October 10 Abstract: We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard CDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ‘observable universe’ and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23σ. Keywords: cosmology: observations — cosmology: theory 1 Introduction description of the expanding universe using spacetime The general relativistic (GR) interpretation of the redshifts diagrams and we provide a mathematical summary in of distant galaxies, as the expansion of the universe, is Appendix A. -
The First Galaxies
The First Galaxies Abraham Loeb and Steven R. Furlanetto PRINCETON UNIVERSITY PRESS PRINCETON AND OXFORD To our families Contents Preface vii Chapter 1. Introduction 1 1.1 Preliminary Remarks 1 1.2 Standard Cosmological Model 3 1.3 Milestones in Cosmic Evolution 12 1.4 Most Matter is Dark 16 Chapter 2. From Recombination to the First Galaxies 21 2.1 Growth of Linear Perturbations 21 2.2 Thermal History During the Dark Ages: Compton Cooling on the CMB 24 Chapter 3. Nonlinear Structure 27 3.1 Cosmological Jeans Mass 27 3.2 Halo Properties 33 3.3 Abundance of Dark Matter Halos 36 3.4 Nonlinear Clustering: the Halo Model 41 3.5 Numerical Simulations of Structure Formation 41 Chapter 4. The Intergalactic Medium 43 4.1 The Lyman-α Forest 43 4.2 Metal-Line Systems 43 4.3 Theoretical Models 43 Chapter 5. The First Stars 45 5.1 Chemistry and Cooling of Primordial Gas 45 5.2 Formation of the First Metal-Free Stars 49 5.3 Later Generations of Stars 59 5.4 Global Parameters of High-Redshift Galaxies 59 5.5 Gamma-Ray Bursts: The Brightest Explosions 62 Chapter 6. Supermassive Black holes 65 6.1 Basic Principles of Astrophysical Black Holes 65 6.2 Accretion of Gas onto Black Holes 68 6.3 The First Black Holes and Quasars 75 6.4 Black Hole Binaries 81 Chapter 7. The Reionization of Cosmic Hydrogen by the First Galaxies 85 iv CONTENTS 7.1 Ionization Scars by the First Stars 85 7.2 Propagation of Ionization Fronts 86 7.3 Swiss Cheese Topology 92 7.4 Reionization History 95 7.5 Global Ionization History 95 7.6 Statistical Description of Size Distribution and Topology of Ionized Regions 95 7.7 Radiative Transfer 95 7.8 Recombination of Ionized Regions 95 7.9 The Sources of Reionization 95 7.10 Helium Reionization 95 Chapter 8. -
Hubble's Diagram and Cosmic Expansion
Hubble’s diagram and cosmic expansion Robert P. Kirshner* Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 Contributed by Robert P. Kirshner, October 21, 2003 Edwin Hubble’s classic article on the expanding universe appeared in PNAS in 1929 [Hubble, E. P. (1929) Proc. Natl. Acad. Sci. USA 15, 168–173]. The chief result, that a galaxy’s distance is proportional to its redshift, is so well known and so deeply embedded into the language of astronomy through the Hubble diagram, the Hubble constant, Hubble’s Law, and the Hubble time, that the article itself is rarely referenced. Even though Hubble’s distances have a large systematic error, Hubble’s velocities come chiefly from Vesto Melvin Slipher, and the interpretation in terms of the de Sitter effect is out of the mainstream of modern cosmology, this article opened the way to investigation of the expanding, evolving, and accelerating universe that engages today’s burgeoning field of cosmology. he publication of Edwin Hub- ble’s 1929 article ‘‘A relation between distance and radial T velocity among extra-galactic nebulae’’ marked a turning point in un- derstanding the universe. In this brief report, Hubble laid out the evidence for one of the great discoveries in 20th cen- tury science: the expanding universe. Hubble showed that galaxies recede from us in all directions and more dis- tant ones recede more rapidly in pro- portion to their distance. His graph of velocity against distance (Fig. 1) is the original Hubble diagram; the equation that describes the linear fit, velocity ϭ ϫ Ho distance, is Hubble’s Law; the slope of that line is the Hubble con- ͞ stant, Ho; and 1 Ho is the Hubble time.