1、This page intentionally left blankGalaxies in the Universe: An IntroductionGalaxies are the places where gas turns into luminous stars, powered by nuclearreactions that also produce most of the chemical elements. But the gas and stars areonly the tip of an iceberg: a galaxy consists mostly of dark m
2、atter, which we knowonly by the pull of its gravity. The ages, chemical composition and motions of thestars we see today, and the shapes that they make up, tell us about each galaxyspast life. This book presents the astrophysics of galaxies since their beginnings inthe early Universe. This Second Ed
3、ition is extensively illustrated with the mostrecent observational data. It includes new sections on galaxy clusters, gammaray bursts and supermassive black holes. Chapters on the large-scale structure andearly galaxies have been thoroughly revised to take into account recent discoveriessuch as dark
4、 energy.The authors begin with the basic properties of stars and explore the MilkyWay before working out towards nearby galaxies and the distant Universe, wheregalaxies can be seen in their early stages. They then discuss the structures ofgalaxies and how galaxies have developed, and relate this to
5、the evolution ofthe Universe. The book also examines ways of observing galaxies across theelectromagnetic spectrum, and explores dark matter through its gravitational pullon matter and light.This book is self-contained, including the necessary astronomical background,and homework problems with hints
6、. It is ideal for advanced undergraduate studentsin astronomy and astrophysics.LINDA SPARKE is a Professor of Astronomy at the University of Wisconsin, anda Fellow of the American Physical Society.JOHN GALLAGHERis the W. W. Morgan Professor of Astronomy at the Universityof Wisconsin and is editor of
7、 the Astronomical Journal.Galaxies inthe Universe:An IntroductionSecond EditionLinda S. SparkeJohn S. Gallagher IIIUniversity of Wisconsin, MadisonCAMBRIDGE UNIVERSITY PRESSCambridge, New York, Melbourne, Madrid, Cape Town, Singapore, So PauloCambridge University PressThe Edinburgh Building, Cambrid
8、ge CB2 8RU, UKFirst published in print formatISBN-13 978-0-521-85593-8ISBN-13 978-0-521-67186-6ISBN-13 978-0-511-29472-3 L. Sparke and J. Gallagher 20072007Information on this title: www.cambridge.org/9780521855938This publication is in copyright. Subject to statutory exception and to the provision
9、of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press.ISBN-10 0-511-29472-7ISBN-10 0-521-85593-4ISBN-10 0-521-67186-8Cambridge University Press has no responsibility for the persistence or accuracy of urls
10、 for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.Published in the United States of America by Cambridge University Press, New Yorkwww.cambridge.orghardbackpaperbackpape
11、rbackeBook (EBL)eBook (EBL)hardbackContentsPreface to the second edition page vii1 Introduction 11.1 The stars 21.2 Our Milky Way 261.3 Other galaxies 371.4 Galaxies in the expanding Universe 461.5 The pregalactic era: a brief history of matter 502 Mapping our Milky Way 582.1 The solar neighborhood
12、592.2 The stars in the Galaxy 672.3 Galactic rotation 892.4 Milky Way meteorology: the interstellar gas 953 The orbits of the stars 1103.1 Motion under gravity: weighing the Galaxy 1113.2 Why the Galaxy isnt bumpy: two-body relaxation 1243.3 Orbits of disk stars: epicycles 1333.4 The collisionless B
13、oltzmann equation 1404 Our backyard: the Local Group 1514.1 Satellites of the Milky Way 1564.2 Spirals of the Local Group 1694.3 How did the Local Group galaxies form? 1724.4 Dwarf galaxies in the Local Group 1834.5 The past and future of the Local Group 188vvi Contents5 Spiral and S0 galaxies 1915.
14、1 The distribution of starlight 1925.2 Observing the gas 2065.3 Gas motions and the masses of disk galaxies 2145.4 Interlude: the sequence of disk galaxies 2225.5 Spiral arms and galactic bars 2255.6 Bulges and centers of disk galaxies 2366 Elliptical galaxies 2416.1 Photometry 2426.2 Motions of the
15、 stars 2546.3 Stellar populations and gas 2666.4 Dark matter and black holes 2737 Galaxy groups and clusters 2787.1 Groups: the homes of disk galaxies 2797.2 Rich clusters: the domain of S0 and elliptical galaxies 2927.3 Galaxy formation: nature, nurture, or merger? 3007.4 Intergalactic dark matter:
16、 gravitational lensing 3038 The large-scale distribution of galaxies 3148.1 Large-scale structure today 3168.2 Expansion of a homogeneous Universe 3258.3 Observing the earliest galaxies 3358.4 Growth of structure: from small beginnings 3448.5 Growth of structure: clusters, walls, and voids 3559 Acti
17、ve galactic nuclei and the early history of galaxies 3659.1 Active galactic nuclei 3669.2 Fast jets in active nuclei, microquasars, and -ray bursts 3839.3 Intergalactic gas 3909.4 The first galaxies 397Appendix A. Units and conversions 407Appendix B. Bibliography 411Appendix C. Hints for problems 41
18、4Index 421Preface to the second editionThis text is aimed primarily at third- and fourth-year undergraduate students ofastronomy or physics, who have undertaken the first year or two of university-levelstudies in physics. We hope that graduate students and research workers in relatedareas will also
19、find it useful as an introduction to the field. Some backgroundknowledge of astronomy would be helpful, but we have tried to summarize thenecessary facts and ideas in our introductory chapter, and we give references tobooks offering a fuller treatment. This book is intended to provide more thanenoug
20、h material for a one-semester course, since instructors will differ in theirpreferences for areas to emphasize and those to omit. After working through it,readers should find themselves prepared to tackle standard graduate texts such asBinney and Tremaines Galactic Dynamics, and review articles such
21、 as those inthe Annual Reviews of Astronomy and Astrophysics.Astronomy is not an experimental science like physics; it is a natural sciencelike geology or meteorology. We must take the Universe as we find it, and deducehow the basic properties of matter have constrained the galaxies that happened to
22、form. Sometimes our understanding is general but not detailed. We can estimatehow much water the Suns heat can evaporate from Earths oceans, and indeed thisis roughly the amount that falls as rain each day; wind speeds are approximatelywhat is required to dissipate the solar power absorbed by the gr
23、ound and theair. But we cannot predict from physical principles when the wind will blowor the rain fall. Similarly, we know why stellar masses cannot be far larger orsmaller than they are, but we cannot predict the relative numbers of stars that areborn with each mass. Other obvious regularities, su
24、ch as the rather tight relationsbetween a galaxys luminosity and the stellar orbital speeds within it, are notyet properly understood. But we trust that they will yield their secrets, just asthe colormagnitude relation among hydrogen-burning stars was revealed as amass sequence. On first acquaintanc
25、e galaxy astronomy can seem confusinglyfull of disconnected facts; but we hope to convince you that the correct analogyis meteorology or botany, rather than stamp-collecting.viiviii Preface to the second editionWe have tried to place material which is relatively more difficult or more intri-cate at
26、the end of each subsection. Students who find some portions heavy goingat a first reading are advised to move to the following subsection and return later tothe troublesome passage. Some problems have been included. These aim mainlyat increasing a readers understanding of the calculations and apprec
27、iation of themagnitudes of quantities involved, rather than being mathematically demanding.Often, material presented in the text is amplified in the problems; more casualreaders may find it useful to look through them along with the rest of the text.Boldface is used for vectors; italics indicate con
28、cepts from physics, or spe-cialist terms from astronomy which the reader will see again in this text, or willmeet in the astronomical literature. Because they deal with large distances andlong timescales, astronomers use an odd mixture of units, depending on the prob-lem at hand; Appendix A gives a
29、list, with conversion factors. Increasing theconfusion, many of us are still firmly attached to the centimetergramsecondsystem of units. For electromagnetic formulae, we give a parallel-text transla-tion between these and units of the Systeme Internationale dUnites (SI), whichare based on meters and
30、 kilograms. In other cases, we have assumed that read-ers will be able to convert fairly easily between the two systems with the aid ofAppendix A. Astronomers still disagree significantly on the distance scale of theUniverse, parametrized by the Hubble constant H0. We often indicate explic-itly the
31、resulting uncertainties in luminosity, distance, etc., but we otherwiseadopt H0= 75 km s1Mpc1. Where ages are required or we venture acrossa substantial fraction of the cosmos, we use the benchmark cosmology withOmega1Lambda1= 0.7,Omega1m= 0.3, and H0= 70 km s1Mpc1.We will use an equals sign (=) for
32、 mathematical equality, or for measuredquantities known to greater accuracy than a few percent; approximate equality ()usually implies a precision of 10%20%, while (pronounced twiddles) meansthat the relation holds to no better than about a factor of two. Logarithms are tobase 10, unless explicitly
33、stated otherwise. Here, and generally in the professionalliterature, ranges of error are indicated by symbols, or shown by horizontal orvertical bars in graphs. Following astronomical convention, these usually refer to1 error estimates calculated by assuming a Gaussian distribution (which is oftenra
34、ther a bad approximation to the true random errors). For those more accustomedto 2 or 3 error bars, this practice makes discrepancies between the results ofdifferent workers appear more significant than is in fact the case.This book is much the better for the assistance, advice, and warnings of ourc
35、olleagues and students. Eric Wilcots test flew a prototype in his undergraduateclass; our colleagues Bob Bless, Johan Knapen, John Mathis, Lynn Matthews, andAlan Watson read through the text and helped us with their detailed comments;Bob Benjamin tried to set us right on the interstellar medium. We
36、are particularlygrateful to our many colleagues who took the time to provide us with figures orthe material for figures; we identify them in the captions. Bruno Binggeli, DapHartmann, John Hibbard, Jonathan McDowell, Neill Reid, and Jerry SellwoodPreface to the second edition ixre-analyzed, re-ran,
37、and re-plotted for us, Andrew Cole integrated stellar energyoutputs, Evan Gnam did orbit calculations, and Peter Erwin helped us out withsome huge and complex images. Wanda Ashman turned our scruffy sketchesinto line drawings. For the second edition, Bruno Binggeli made us an improvedportrait of the
38、 Local Group, David Yu helped with some complex plots, and TammySmecker-Hane and Eric Jensen suggested helpful changes to the problems. Muchthanks to all!Linda Sparke is grateful to the University of Wisconsin for sabbatical leavein the 19967 and 20045 academic years, and to Terry Millar and the Uni
39、-versity of Wisconsin Graduate School, the Vilas Foundation, and the WisconsinAlumni Research Foundation for financial support. She would also like to thankthe directors, staff, and students of the Kapteyn Astronomical Institute (Gronin-gen University, Netherlands), the Mount Stromlo and Siding Spri
40、ng Observato-ries (Australian National University, Canberra), and the Isaac Newton Institutefor Mathematical Sciences (Cambridge University, UK) and Yerkes Observatory(University of Chicago), for their hospitality while much of the first edition waswritten. She is equally grateful to the Dominion As
41、trophysical Observatory ofCanada, the Max Planck Institute for Astrophysics in Garching, Germany, andthe Observatories of the Carnegie Institute of Washington (Pasadena, California)for refuge as we prepared the second edition. We are both most grateful to ourcolleagues in Madison for putting up with
42、 us during the writing. Jay Gallagheralso thanks his family for their patience and support for his work on The Book.Both of us appear to lack whatever (strongly recessive?) genes enable accurateproofreading. We thank our many helpful readers for catching bugs in the firstedition, which we listed on
43、a website. We will do the same for this edition, andhope also to provide the diagrams in machine-readable form: please see links fromour homepages, which are currently at www.astro.wisc.edu/sparke and jsg.1IntroductionGalaxies appear on the sky as huge clouds of light, thousands of light-years acros
44、s:see the illustrations in Section 1.3 below. Each contains anywhere from a millionstars up to a million million (1012); gravity binds the stars together, so they donot wander freely through space. This introductory chapter gives the astronomicalinformation that we will need to understand how galaxi
45、es are put together.Almost all the light of galaxies comes from their stars. Our opening sectionattempts to summarize what we know about stars, how we think we know it, andwhere we might be wrong. We discuss basic observational data, and we describethe life histories of the stars according to the th
46、eory of stellar evolution. Even thenearest stars appear faint by terrestrial standards. Measuring their light accuratelyrequires care, and often elaborate equipment and procedures. We devote the finalpages of this section to the arcana of stellar photometry: the magnitude system,filter bandpasses, a
47、nd colors.In Section 1.2 we introduce our own Galaxy, the Milky Way, with its charac-teristic flying saucer shape: a flat disk with a central bulge. In addition to theirstars, our Galaxy and others contain gas and dust; we review the ways in whichthese make their presence known. We close this sectio
48、n by presenting some of thecoordinate systems that astronomers use to specify the positions of stars within theMilky Way. In Section 1.3 we describe the variety found among other galaxies anddiscuss how to measure the distribution of light within them. Only the brightestcores of galaxies can outshin
49、e the glow of the night sky, but most of their lightcomes from the faint outer parts; photometry of galaxies is even more difficultthan for stars.One of the great discoveries of the twentieth century is that the Universe is notstatic, but expanding; the galaxies all recede from each other, and from us. OurUniverse appears to have had a beginning, the Big Bang, that was not so far in thepast: the cosmos is only about three times older than the Earth. Section 1.4 dealswith the cosmic expansion, and how it affects the light we receive from galaxies.Fina
