Astronomy And Astrophysics In The New Millennium: An Overview
Astronomy and Astrophysicsin the New Millenniuman overviewAstronomy and Astrophysics Survey CommitteeBoard on Physics and AstronomySpace Studies BoardDivision on Engineering and Physical SciencesNational Research CouncilNational Academy PressWashington, D.C.
ABOUT THE NATIONAL ACADEMIESFor more than 100 years, the National Academies have provided independent advice on issues of science, technology,and medicine that underlie many questions of national importance. The National Academies—comprising the NationalAcademy of Sciences, the National Academy of Engineering, the Institute of Medicine, and the National ResearchCouncil—work together to enlist the nation’s top scientists, engineers, health professionals, and other experts to studyspeci c issues. The results of their deliberations have inspired some of America’s most signi cant and lasting efforts toimprove the health, education, and welfare of the nation. To learn more about Academies’ activities, check the Website at www.nationalacademies.org.The project that is the subject of this report was approved by the Governing Board of the National Research Council,whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering,and the Institute of Medicine. The members of the committee whose work this report summarizes were chosen for theirspecial competences and with regard for appropriate balance.This project was supported by the National Aeronautics and Space Administration under Grant No. NAG5-6916, theNational Science Foundation under Grant No. AST-9800149, and the Keck Foundation.Additional copies of this report are available from:Board on Physics and Astronomy, National Research Council, HA 562, 2101 Constitution Avenue, N.W., Washington, DC20418; Internet http://www.nationalacademies.org/bpa .Copyright 2001 by the National Academy of Sciences. All rights reserved.Printed in the United States of AmericaAstronomy and Astrophysics in the New Millennium: an overview
BOARD ON PHYSICS AND ASTRONOMYASTRONOMY AND ASTROPHYSICSSURVEY COMMITTEECHRISTOPHER F. McKEE, University of California, Berkeley, Co-chairJOSEPH H. TAYLOR, JR., Princeton University, Co-chairTODD BOROSON, National Optical Astronomy ObservatoriesWENDY FREEDMAN, Carnegie ObservatoriesDAVID J. HOLLENBACH, NASA Ames Research Center, Executive Of cerDAVID C. JEWITT, University of HawaiiSTEVEN M. KAHN, Columbia UniversityJAMES M. MORAN, JR., Smithsonian Astrophysical ObservatoryJERRY E. NELSON, University of California ObservatoriesR. BRUCE PARTRIDGE, Haverford CollegeMARCIA RIEKE, University of ArizonaANNEILA SARGENT, California Institute of TechnologyALAN TITLE, The Lockheed-Martin Space Technology CenterSCOTT TREMAINE, Princeton UniversityMICHAEL S. TURNER, University of ChicagoNational Research Council StaffDONALD C. SHAPERO, Board on Physics and Astronomy, DirectorJOSEPH K. ALEXANDER, Space Studies Board, DirectorJOEL R. PARRIOTT, Senior Program Of cerROBERT L. RIEMER, Senior Program Of cerGRACE WANG, Administrative Associate (1998-1999)SÄRAH CHOUDHURY, Administrative Associate (1999-present)MICHAEL LU, Project Assistant (1998-2000)NELSON QUIÑONES, Project Assistant (2000-present)ROBERT C. DYNES, University of California at San Diego, ChairROBERT C. RICHARDSON, Cornell University, Vice ChairGORDON A. BAYM, University of Illinois at Urbana-ChampaignWILLIAM BIALEK, NEC Research InstituteVAL FITCH, Princeton UniversityRICHARD D. HAZELTINE, University of Texas at AustinJOHN HUCHRA, Harvard-Smithsonian Center for AstrophysicsJOHN C. MATHER, NASA Goddard Space Flight CenterCHERRY ANN MURRAY, Lucent TechnologiesANNEILA I. SARGENT, California Institute of TechnologyJOSEPH H. TAYLOR, JR., Princeton UniversityKATHLEEN TAYLOR, General Motors Research and Development CenterJ. ANTHONY TYSON, Bell Labs, Lucent TechnologiesCARL E. WIEMAN, JILA/University of Colorado at BoulderPETER G. WOLYNES, University of Illinois at Urbana-ChampaignDONALD C. SHAPERO, DirectorSPACE STUDIES BOARDCLAUDE R. CANIZARES, Massachusetts Institute of Technology, ChairMARK R. ABBOTT, Oregon State UniversityFRAN BAGENAL, University of ColoradoDANIEL N. BAKER, University of ColoradoROBERT E. CLELAND, University of WashingtonMARILYN L. FOGEL, Carnegie Institution of WashingtonBILL GREEN, former member, U.S. House of RepresentativesJOHN H. HOPPS, JR., Rozewell, GeorgiaCHRIS J. JOHANNSEN, Purdue UniversityRICHARD G. KRON, University of ChicagoJONATHAN I. LUNINE, University of ArizonaROBERTA BALSTAD MILLER, Columbia UniversityGARY J. OLSEN, University of Illinois at Urbana-ChampaignMARY JANE OSBORN, University of Connecticut Health CenterGEORGE A. PAULIKAS, The Aerospace CorporationJOYCE E. PENNER, University of MichiganTHOMAS A. PRINCE, California Institute of TechnologyPEDRO L. RUSTAN, JR., U.S. Air Force (retired)GEORGE L. SISCOE, Boston UniversityEUGENE B. SKOLNIKOFF, Massachusetts Institute of TechnologyMITCHELL SOGIN, Marine Biological LaboratoryNORMAN E. THAGARD, Florida State UniversityALAN M. TITLE, Lockheed Martin Advanced Technology CenterRAYMOND VISKANTA, Purdue UniversityPETER W. VOORHEES, Northwestern UniversityJOHN A. WOOD, Harvard-Smithsonian Center for AstrophysicsJOSEPH K. ALEXANDER, Director
ACKNOWLEDGMENTSText drafted by Donald Goldsmith.Layout and graphic design by Robert Sokol.Additional contributions to the text from Alan Dressler, Christopher McKee, Donald Shapero, and Joel Parriott.This report was reviewed in draft form by Gordon Baym, University of Illinois at Urbana-Champaign; Anita Cochran, University of Texas; SharonDunwoody, University of Wisconsin; Sandra Faber, University of California, Santa Cruz; John Huchra, Harvard-Smithsonian Center for Astrophysics;Richard McCray, University of Colorado; and J. Anthony Tyson, Bell Labs, Lucent Technologies. The review was overseen by Lewis Branscomb, HarvardUniversity. Responsibility for the nal content of this report rests entirely with the authors and the institution.IMAGE CREDITSCover:Page 8:Page 9:PagePagePagePagePage10:11:12:13:14:Page 15:Page 16:Page 17:Page 18:Page 19:Page 20:Page 21:Page 22:Page 23:Page 24:Page 25:Page 26:Page 27:Page 28:Ground-based optical image of the Andromeda Galaxy (aka Messier 31). The Andromeda Galaxy is a large spiral galaxy—similarto our own galaxy, the Milky Way—and a close neighbor at a distance of about 2 million light-years. Courtesy of T.A. Rector and B.A. Wolpa(National Optical Astronomy Observatory/Association of Universities for Research in Astronomy/National Science Foundation).Courtesy of the MAXIMA Collaboration.Radio image courtesy of T.M. Dame, Dap Hartmann, and P. Thaddeus (Harvard-Smithsonian Center for Astrophysics). Infrared, x-ray, andgamma-ray images courtesy of NASA and provided by the Astrophysics Data Facility. Optical image courtesy of A. Mellinger (Universityof Potsdam).Courtesy of the Space Telescope Science Institute.Courtesy of J. Lawrence (NASA Goddard Space Flight Center).Courtesy of NASA and the Hubble Heritage Team (Space Telescope Science Institute).Courtesy of the New Initiatives Of ce at the Association of Universities for Research in Astronomy.Optical image courtesy of P. Scowen and J. Hester (Arizona State University) and Mt. Palomar Observatories. X-ray image courtesy of NASA,the Chandra X-ray Observatory Center, and the Smithsonian Astrophysical Observatory.Constellation-X illustration courtesy of NASA Goddard Space Flight Center. G292.0 1.8 image courtesy of NASA, the Chandra X-rayObservatory Center, and J. Hughes et al. (Rutgers University).Courtesy of NASA and E. Schreier (Space Telescope Science Institute).Both images courtesy of the National Radio Astronomy Observatory.Courtesy of P. Scowen and J. Hester (Arizona State University) and NASA.Courtesy of Doug Johnstone (National Research Council of Canada), John Bally (University of Colorado), and NASA.Courtesy of NASA, the Space Telescope Science Institute, and the High-Z SN Search Team.Asteroid image courtesy of NASA, the Jet Propulsion Laboratory, California Institute of Technology, and the National Space Science Data Center.Gravitational lens image courtesy of W.N. Colley and E. Turner (Princeton University), J. Anthony Tyson (Bell Labs, Lucent Technologies),and NASA.Scienti c calculation by M. Miller, W.-M. Suen, and M. Tobias (Washington University); visualization by Werner Benger (Albert-EinsteinInstitut/Konrad-Zuse-Zentrum fuer Informationstechnik).Courtesy of W. Folkner (Jet Propulsion Laboratory, California Institute of Technology).Courtesy of the SOHO/EIT Consortium. The Solar and Heliospheric Observatory is an international project conducted by theEuropean Space Agency and NASA.Courtesy of the SOHO/EIT Consortium. The Solar and Heliospheric Observatory is an international project conducted by theEuropean Space Agency and NASA.Courtesy of NASA and the Hubble Heritage Team (Space Telescope Science Institute).Courtesy of the Jet Propulsion Laboratory, California Institute of Technology.Courtesy of NASA and the Hubble Heritage Team (Space Telescope Science Institute).Astronomy and Astrophysics in the New Millennium: an overview
Contents6ASTRONOMY AND ASTROPHYSICSIN THE NEW MILLENNIUM8THE TELESCOPE AS A TIME MACHINE10THE FIRST SOURCES OF LIGHTIN THE UNIVERSE12HOW GALAXIES TOOK SHAPE14VIOLENT EVENTS IN THE COSMOS16WHAT HAPPENS AT THE HEART OF A GALAXY18THE ORIGINS OF STARS AND PLANETS20SURVEYING THE UNIVERSEWITH INCREASED ACCURACY22GRAVITATIONAL RADIATION:A NEW WAY TO SEE THE COSMOS24SOLAR ASTROPHYSICS26THE QUEST TO FIND OTHER EARTHS28HIGH-PRIORITY PROJECTSIN ASTRONOMY AND ASTROPHYSICS
Astronomy and AstrophysicsAstronomers Explore the UniverseSTRONOMY and Astrophysics in the New MillenniumAhorizons, enlarged by observations made from every part of ouris the most recent in a series of surveys ofplanet and above it, had expanded to include the entire universe.of leading astronomers. The current survey, authored bythe Milky Way Galaxy, which itself is but one of trillions of galaxiesthe field conducted once every 10 years by committeesthe Astronomy and Astrophysics Survey Committee, providesrecommendations for a research program for the decadethat addresses the key scientific questionsconfronting astronomers andastrophysicists today.Today we know that the Sun is but one of 300 billion stars inwithin the visible universe. By peering billions oflight-years into space, telescopes look billions ofyears into the past to observe the cosmos whenit was young. Astronomers can now interpretwhat they see within the framework of a well-The explosion oftested model, called the inflationary Big Bangknowledge intheory. This theory describes how the cosmosrecent years, madehas evolved since the first 10–36 second ofpossible by currentcosmic time, the moment of the Big Bangfacilities, has in turnthat began the universe. The universe hasraised a wealth ofbeen expanding ever since that moment.intriguing new questionsDuring the first billion years after theabout the universe and itsBig Bang, galaxies and galaxy clustersconstituent galaxies, stars,began to emerge from a relativelyand planets. To answerfeatureless cosmos. Most of thethem, astronomers will needmatter in the universe exists ina diverse array of increasinglythe form of dark matter, whosecapable 21st-century tools.nature remains a mystery butCurrent challenges in astronomywhose existence is convincinglyand astrophysics, and thededuced from its gravitationalresearch initiatives that the surveyeffect on visible matter.report recommends to addressStartling new observationalthem (see p. 28), are the subject ofevidence points to an eventhis booklet.more mysterious darkOne millennium ago, the fewenergy that pervades theastronomers working on Earth—in Asiauniverse, driving the(particularly in China), in the MiddleEast, and in Mesoamerica—knew of onlysix of the nine planets that orbit the Sun.expansion to ever-greater velocities astime goes on.One cannot, of course, predict what astronomers will tell us inAlthough they studied the stars, they did notthe year 3000 A.D., or even in 2100 A.D. For the foreseeableunderstand that these points of light were as mighty as our ownfuture of the next few decades, we can, however, summarizeSun, nor could they imagine the vast distances that separate thesethe defining issues for astronomy and astrophysics by posing fivestars from Earth. One millennium later humanity’s astronomicalfundamental questions:Cover of the current survey report.Astronomy and Astrophysics in the New Millennium: an overview
in the New Millenniumm How did the universe begin, how did it evolve from a primordial soupm Search for life beyond Earth, and, if it is found, determine its natureof elementary particles into the complex structures we see today, andand its distribution in the Milky Way Galaxy. This goal is so challengingwhat fate lies in store for the cosmos?and of such importance that it could occupy astronomers for theforeseeable future. The search for evidence of life beyond Earthm How do galaxies first arise and mature?m How are stars born and how do they live and die?m How do planets form and change as they age?m Does life exist elsewhere in the universe?Researchers have now begunto gather the fundamentalobservational data that will one dayanswer all of these questions. Foronly one do we already have a fairlycomplete answer: We know aboutthe lives of stars. The developmentand observational validation ofthe theory of what astronomerscall stellar evolution was arguablythe greatest accomplishment of20th-century astrophysics. For thenew century, astronomers’ long-through remote observation is a major focus of the new interdisciplinaryfield of astrobiology.m Use the universe as a unique laboratory to test the known laws ofphysics in regimes that are not accessible on Earth and to search forentirely new physics. It is remarkable thatFthe laws of physics developed on EarthOURTEEN billion years of cosmic evolutionsince the Big Bang have spawned themighty zoo of cosmic objects that populate theuniverse today. On one of these objects lives aspecies on the verge of tting together the piecesof this puzzle of how the universe came to be theway it is. We humans are about to understandhow we came to inhabit a small rocky planet inorbit around a rather average star in the outerarms of the spiral galaxy we call the Milky Way.That understanding will reveal to us the ultimatefate of the universe.and destiny of the universe, and of its constituent galaxies, stars,and planets, which include the Milky Way, the Sun, and Earth.To achieve this goal, the Astronomy and Astrophysics SurveyCommittee believes that astronomers should carry out thefollowing program of observational and theoretical research:m Map the distribution of galaxies, gas, and dark matter in the universe,and survey the stars and planets in the Milky Way. Mapping thedistant universe will help to reveal the formation of galaxies in theearly universe and their maturation to the present, the evolution ofprimordial hydrogen and helium gas created in the Big Bang into gasenriched with almost all of the elements found in the periodic table,and the distribution and nature of the mysterious dark matter thatconstitutes most of the matter in the universe. Surveys within the MilkyWay will help to reveal how stars and planets are created in collapsingclouds of gas and dust and the variety and abundance of planetarysystems.occurring billions of light-years awayand under extreme conditions radicallydifferent from those under which the lawswere derived and tested. Researchershave only begun to probe the conditionsnear the event horizons of black holesor in the very early universe. In theseenvironments, the tests of the laws ofphysics will be much more stringent. Newphysical processes may be revealed thatshed light on the unification of the forcesand particles of nature.term goal is to assemble a detailedpicture of the formation, evolution,appear to be consistent with phenomenam Develop a conceptual framework that accounts for the complete rangeof astronomical observations. As with all scientific theories, such aframework must be subject to continual checks by further observation.For the new decade, astronomers are poised to make progressin five particular areas:1. Determining the large-scale properties of the universe: its age, thetypes of matter and energy that it contains, and the history of itsexpansion;2. Studying the dawn of the modern universe, when the first stars andgalaxies formed;3. Understanding the formation and growth of black holes of all sizes;4. Studying the formation of stars and their planetary systems,including the birth and evolution of giant and terrestrial planets;and5. Understanding the effects of the astronomical environment onEarth.
The Telescope as a Time MachineSTRONOMY is history. Because light takes timeAdetected. Some of these objects are galaxies seen during theirto travel from one place to another, we see objectsearly developmental stages when they were rich in young, hot,not as they are now but as they were at the time when theyand very luminous stars. To peer still farther back through time,released the light that has traveled across the universe to us.to reach the era when stars first began to shine, astronomersAstronomers can therefore look farther back through time byneed a telescope that can detect extremelystudying progressivelylow intensities of infrared light. Astronomersmore-distantobjects.need sensitivity in the infrared part ofthe spectrum because theThe chieflight from these youngdifficulty instars in distant galaxies,employing this “timeeven though emittedmachine” to observeas visible light, has beenthe cosmos during itsstretched by thepast epochs arises fromthe fact that distantexpansion of the universe toappear to us as infrared light.objects appear fainterThe Hubble Spacethan closer ones. WeTelescope can observe themust therefore captureshortest-wavelength portion ofand analyze the light fromthe infrared domain, but itsprogressively dimmer2.4-meter mirror is too warmobjects as we push fartherand too small to detect theback into the past.faint glow from the most distantSpecialized instruments areyoung galaxies. To observe galaxiesneeded to study ourin their earliest epochs, the surveynearest neighbor, thereport recommends a new, advanced-Andromeda Galaxy, whichtechnology telescope designed to workis 2 million light-years away.best in the infrared part of theBut this companion of thespectrum. In an orbit a million miles fromMilky Way shines a million times more brightly than a similarEarth, this telescope will become so cold that its own infraredgalaxy seen at a distance of 2 billion light-years! This comparisonglow will be insignificant compared with the light from the distantgives a sense of how difficult it will be to obtain images of objectsgalaxies, something an earthbound telescope could never achieve.formed close to the Big Bang era more than 10 billion years ago.Also, being above Earth’s veil of air allows us to see radiationDuring the past few years, the Hubble Space Telescope hasthat cannot penetrate it, and guarantees the sharpest imagesobtained long-exposure images that reveal the faintest objects everImage of tiny uctuations in the universe’s oldest light, only 300,000 yearsafter the Big Bang. There is no way for astronomers to see farther backthan this electromagnetic brick wall. Future tools for detecting gravitationalradiation offer the promise of breaking through this wall to even earlier times.the telescope can deliver, free from the turbulence in Earth’satmosphere that handicaps telescopes on the ground.Astronomy and Astrophysics in the New Millennium: an overview
N their quest to improve our ability to observe theIlonger wavelengths. Though human eyes cannot perceive this radiation,universe, astronomers have followed two lines of technologicalthese domains are just as rich in information as the visible light with
Astronomy and Astrophysics in the New Millennium: an overview ACKNOWLEDGMENTS Cover: Ground-based optical image of the Andromeda Galaxy (aka Messier 31). The Andromeda Galaxy is a large spiral galaxy—similar to our own galaxy, the Milky Way—and a close neighbor at a distance of about 2 million light-years. Courtesy of T.A. Rector and B.A. Wolpa
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