Adventures In Cosmology

Application of Total Innovation Management in China's SMEs' Study

David Goodstein

• Publisher: WSPC
• Year: 2011
• ISBN:
  9789814390606
• Topic: Biological Sciences
• Subtopic: Science General
• Index: Biological Sciences

This volume tells of the quest for cosmology as seen by some of the finest cosmologists in the world. It starts with “Galaxy Formation from Start to Finish” and ends with “The First Supermassive Black Holes in the Universe,” exploring in between the grand themes of galaxies, the early universe, expansion of the universe, dark matter and dark energy. This up-to-date collection of review articles offers a general introduction to cosmology and is intended for all probing into the profound questions on where we came from and where we are going.

Contents:

• Galaxy Formation: From Start to Finish (Andrew Benson, California Institute of Technology)
• The Reionization of Cosmic Hydrogen by the First Galaxies (Abraham Loeb, Harvard University)
• Clusters of Galaxies (Elena Pierpaoli, University of Southern California)
• Reionizing the Universe with the First Sources of Light (Volker Bromm, University of Texas at Austin)
• Mapping the Cosmic Dawn (Steven Furlanetto, University of California, Los Angeles)
• Neutrino Masses from Cosmology (Ofer Lahav and Shaun Thomas, University College London)
• Measuring the Expansion Rate of the Universe (Laura Ferrarese, Herzberg Institute of Astrophysics)
• Particles as Dark Matter (Dan Hooper, The University of Chicago)
• Detection of WIMP Dark Matter (Sunil Golwala, California Institute of Technology & Dan McKinsey, Yale University)
• The Accelerating Universe (Dragan Huterer, University of Michigan)
• Frontiers of Dark Energy (Eric V Linder, University of California, Berkeley and Ewha Womans University)
• The First Supermassive Black Holes in the Universe (Xiaohui Fan, University of Arizona)

Readership: Students, researchers and academics interested in cosmology.

CHAPTER 1

INTRODUCTION

Many non-scientists tend to think that cosmology became a science only in our own time, prior to which it was a vague system of beliefs that did not amount to much. But in fact the Greeks were cosmological scientists (Plato, Aristotle and many who predated those two), and the tradition continued with Ptolemy in second-century Alexandria, and especially with the likes of Copernicus, Kepler, Galileo, and Isaac Newton. Each of those thinkers had a vision of how the Universe works and tried to arrange the empirical facts to fit that vision. That is what cosmology is all about. This book presents essays on the current state of the art by their modern counterparts.

To begin with, Andrew Benson, a senior research fellow in theoretical cosmology in the TAPIR (Theoretical Astrophysics Including Relativity) group at Caltech and a member of Caltech’s Moore Center for Theoretical Cosmology and Physics, tells us all about how galaxies were formed in the early Universe. Galaxy formation, he says, is a process, as opposed to being an event, and is one that is on-going. The formation occurs as the galaxy’s constituent matter is drawn together by the force of gravity in spite of the accelerating expansion of the Universe. Dark matter halos (the dark matter surrounding a galaxy) and small density fluctuations all play an important role in galaxy formation.

Abraham Loeb, director of the Institute for Theory and Computation at Harvard University, describes the period, starting 400 000 years after the Big Bang, when the plasma of subatomic particles had cooled enough for them to combine into hydrogen atoms and a lesser amount of helium atoms, along with a few other light elements. It was at just this moment when small fluctuations in the density of matter started to grow into galaxies.

Then Elena Pierpaoli tells us about clusters of galaxies, including their structure formation, how we observe them and their role in cosmology.

Volker Bromm, Assistant Professor in the Department of Astronomy, University of Texas at Austin, considers the period of reionization that brought an end to the cosmic dark ages, when “reionization” brought forth the first stars, galaxies, and even spawned the black holes that are thought to exist everywhere in the Universe.

Steven Furlanetto, Associate Professor of Physics and Astronomy at UCLA, gives us a picture of the formation of the earliest galaxies taken largely from the study of spin-flip interactions (whose 21 cm wavelengths are easily detectable as radio-waves).

Laura Ferrarese, Senior Research Officer of the National Research Council of Canada, shows us how to measure the expansion of the Universe using various methods to get the distances to stars. Type Ia supernovae and cepheid variable stars both serve as “standard candles” to calculate distances; they give us one important scale. Other methods involve the Tip of the Red Giant Branch (TRGB), the Surface Brightness Fluctuation (SBF), and the Tully–Fisher relation.

Dan Hooper, Assistant Professor of Astronomy and Astrophysics at the University of Chicago, speculates on the possible nature of dark matter — exotic, nonbaryonic material that is thought to constitute 80–85% of the matter in the Universe. He argues against a modification of Newtonian dynamics and for such the favorite candidate is WIMPs (Weakly Interacting Massive Particles). He brings forward the view that the mutual annihilation of these particles and their antiparticles slowed as the Universe expanded, leaving large numbers of them present.

Sunil Golwala and Dan McKinsey, respectively Associate Professor of Physics at Caltech and at Yale University, review the methods by which we may be able to detect WIMPS — if indeed they exist.

Dragan Huterer, Assistant Professor of Physics at the University of Michigan tells us about the current acceleration of the Universe’s expansion: How was it discovered? How long has this present epoch been? And how is the dark energy causing the acceleration phenomenologically described?

Eric Linder, codirector of the Institute for Nuclear and Particle Astrophysics at the Lawrence Berkeley National Laboratory, writes regarding what is yet unknown about dark energy: whether it is uniform, dynamic, disappears at early times, or whether its origin is of quantum or gravitational nature. They are valid possibilities, and carry profound implications for the frontiers of physics and the fate of the Universe. Even though our knowledge of dark matter is very limited, we are taking initial steps for such advancement.

Xiaohui Fan, Professor of Astronomy at the University of Arizona, looks into the matter of supermassive black holes that, while accreting mass, often outshine entire galaxies. Supermassive black holes are thought to power the quasistellar radio sources known as quasars — the most luminous objects in the Universe — and related objects known as AGNs (Active Galactic Nuclei).

All in all these modern cosmologists give us a remarkably detailed view of what the Universe is all about and what we do not yet know about it.

CHAPTER 2

GALAXY FORMATION: FROM START TO FINISH

ANDREW BENSON

Theoretical Astrophysics Including Relativity (TAPIR)
California Institute of Technology
Pasadena, CA 91125, USA

It was once observed¹ that galaxy formation “is a process, not an event”, meaning that galaxies began forming rather quickly (by cosmological standards) after the Big Bang and are still forming today. Galaxy formation is a consequence of the remarkable ability of gravity to organize matter over cosmological scales, even in the face of cosmic expansion. In this chapter, we will explore the physical processes that control the process of galaxy formation and how they shape the properties of galaxies, both at the present day and in the early Universe.

2.1 Historical Perspective

The first detailed observations of galaxies external to our own (neglecting the Magellanic Clouds, which have undoubtedly been viewed by human eyes for many millennia) were made by the Earl of Rosse, using a 72-inch telescope which he had constructed in Birr, Ireland. Lord Rosse made sketches showing the spiral structure of galaxies such as M51, such as the one shown in Fig. 2.1. Galaxies, or simply “spiral nebulae” as they were then known, have been the subject of much debate ever since.

Fig. 2.1 A sketch of M51, the Whirlpool Galaxy, made by Lord Rosse in 1845 as observed though his 72-inch telescope. Rosse did not know that this was an external galaxy, but could clearly see the spiral arms and even the smaller, companion galaxy NGC 5195 (to the right) which may well have triggered the formation of the strong spiral pattern as it passed through the disk of M51.

Their true nature remained uncertain for a long time. For example, at the start of the 20th century many believed that they were proto-planetary systems, with Sir Robert Ball of Cambridge University writing in his book In The High Heavens (all, 190):

Probably this nebula [M51] will in some remote age gradually condense down into more solid substances. It contains, no doubt, enough material to make many globes as big as our Earth.

In fact, both Thomas Wright and Immanuel Kant had suggested that the spiral nebulae were actually “island-universes”, i.e. stellar systems comparable to our own Milky Way, rather than small gaseous nebulae within the Milky Way. The debate as to whether spiral nebulae were galactic or extragalactic was famously taken up by Shapley, who favored a galactic explanation, and Curtis, who took the opposite view (Shapley and Curtis, 1921). The debate ran for nearly five years in the early 1920s, and was not fully resolved until 1924 when Edwin Hubble measured the distance to the Andromeda galaxy (M31) by observing a Cepheid variable star² in the outskirts of that galaxy (Hubble, 1929). The distance to M31, which is now known to be around 1 Mpc (Megaparsec; 1 Mpc ≈ 3.1 × 10²² m), proved conclusively that it lay outside of the Milky Way, which was already known to be much smaller than this (Shapley, 1919).

2.2 The Universe Before Galaxies

Galaxy formation has been an ongoing process throughout most of the history of the Universe. If, however, we examine the history of the Universe on a logarithmic time axis, from the Planck time at 5 × 10⁻⁴⁴s to the present day at 4.3 × 10¹⁷ s, galaxy formation occupies just slightly over two of those 61 logarithmic decades. A lot happened in the remaining 59 decades, including inflation (which, importantly, laid down the density perturbations, from which galaxies would eventually form, in the otherwise homogeneous Universe), nucleosynthesis, recombination (during which the Universe first become sufficiently cool for electrons and protons to combine to form hydrogen) and the extended “dark ages” after recombination but prior to the first stars forming (to be discussed in Sec. 2.3.1). Those topics are discussed elsewhere in this volume.

Looking out into the Universe we are also looking back in time, due to the finite speed with which light travels. Cosmologists usually specify the distance to a galaxy (and, therefore, the time at which the light we receive from it was emitted) in terms of redshift. The redshift, denoted by z, measures the factor by which the wavelengths of photons emitted by a distant galaxy have been stretched due to the expansion of the Universe in the intervening time, such that the observed and emitted wavelengths, λ_o and λ_e respectively, are related by λ_o = (1 + z)λ_e. Referring to some point in cosmic history as “redshift z” implies a time at which the Universe was smaller by a factor of 1 + z in each linear dimension (such that today corresponds to z = 0 and the Big Bang³ to z = ∞). Figure 2.2 shows the relation between redshift and the age of our Universe, and indicates a few key epochs in the Universe’s history that will be discussed below.

Fig. 2.2 The relation between the age of the Universe and redshift (the extent to which wavelengths of light have been shifted from their values at emission by the expansion of the Universe). The present day corresponds to z = 0 and an age of approximately 13.8 Gyr. Also shown are some of the key epochs in cosmic history: the “dark ages” (see Sec. 2.3.1), the epoch of first light (see Sec. 2.3.2), the epoch of reionization (see Sec. 2.3.3), the time at which feedback from active galactic nuclei (AGN) begins to shut down star formation (see Sec. 2.3.5) and the time at which dark energy begins to dominate the expansion of the Universe.

Galaxy formation studies usually take as their initial conditions the Universe at redshifts of around z ≈ 50–100, prior to the formation of any galaxy, when the material content of the Universe consists of almost uniformly distributed dark matter and gas, with small density perturbations in the dark matter component gradually growing under their own self-gravity. The statistical properties of those perturbations are predicted in the inflationary paradigm in a Universe dominated by cold dark matter,⁴ and are measured directly from the cosmic microwave background (CMB; the relic radiation left over from the Big Bang).

The goal of galaxy formation studies then is to understand how the near uniform distribution of dark matter and gas evolved over a period of around 13 billion years to form the population of galaxies with a rich phenomenology as seen today.

2.3 The Story So Far

2.3.1 The end of the dark ages

After protons and electrons recombined⁵ at z ≈ 1100 and the CMB radiation began its journey toward us, the Universe entered a long period of quiescence known as the Dark Ages during which no luminous sources, stars or accreting black holes, existed. This apparent quiescence neglects the fact that much activity was underway in the dark sector. The ripples in the density of dark matter seeded by inflation and which were tiny at the epoch of recombination were gradually growing under their own self-gravity during this period. Gravitational collapse is usually a runaway process, with density increasing exponentially in time. This rapid growth is mitigated cosmologically by the expansion of the Universe which reduces that expo...

Table of contents

• Cover
• Half title
• Title
• Copyright
• Contents
• 1. Introduction
• 2. Galaxy Formation: From Start to Finish
• 3. The Reionization of Cosmic Hydrogen by the First Galaxies
• 4. Clusters of Galaxies
• 5. Reionizing the Universe with the First Sources of Light
• 6. Mapping the Cosmic Dawn
• 7. Neutrino Masses from Cosmology
• 8. Measuring the Expansion Rate of the Universe
• 9. Particles as Dark Matter
• 10. Detection of WIMP Dark Matter
• 11. The Accelerating Universe
• 12. Frontiers of Dark Energy
• 13. The First Supermassive Black Holes in the Universe
• Index