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General Disclaimer One or more of the Following Statements may affect this Document This document has been reproduced from the best copy furnished by the organizational source. It is being released in the interest of making available as much information as possible. This document may contain data, which exceeds the sheet parameters. It was furnished in this condition by the organizational source and is the best copy available. This document may contain tone-on-tone or color graphs, charts and/or pictures, which have been reproduced in black and white. This document is paginated as submitted by the original source. Portions of this document are not fully legible due to the historical nature of some of the material. However, it is the best reproduction available from the original submission. Produced by the NASA Scientific and Technical Information Program ) ( NASA 'SP-46 + i • GPO PRICE $ OTS PRICE(S) $ Hard copy (HC) EDITED BY Microfiche (MF) Stephen P. Maran AND A. G. W. Cameron GODDARD INSTITUTE FOR SPACE STUDIES NATIONAL AERONAUTICS AND SPACE ADMINISTRATION L 4. PHYSICSOF •NONTHERMAL RADIOSOURCES PHYSICSOF NONTHERMAL RADIOSOURCES NASA SP-46 EDITED BY Stephen P. Maran GODDARD INSTITUTE FOR SPACE STUDIES and DEPARTMENT OF ASTRONOMY UNIVERSITY OF MICHIGAN AND A. G. W. Cameron GODDARD INSTITUTE FOR SPACE STUDIES GODDARD INSTITUTE FOR SPACE STUDIES NATIONAL AERONAUTICS AND SPACE ADMINISTRATION JUNE 1964 COVER ILLUSTRATIONS Front cover-- Artist R. Catinella's impression of the central region of Messier 87, giant elliptical galaxy in the Virgo Cluster (distance approximately 36 million light years), which has been identified as a strong source of radio emission. The famous "jet" emits optical synchrotron radiation. Back cover-- An unusally broad dust lane is the most striking fea- ture of the peculiar galaxy NGC 5128 (distance approximately 13 million light years), which has been identified with the strong radio source Centaurus A. (McDonald Observatory) For sale by the Superintendent of Documents, U.S. Government Printing Office Washing-ton. D.C. 20402 - Price 75 cents Table of Contents Page INTRODUCTION ................................... vii RADIO OBSERVATIONS A Survey of the Spectra of Radio Sources R. G. Conway .................................. 1 Brightness Distributions in Nonthermal Radio Sources A. T. Moffet ..................................... 19 Linear Polarization Effects in Radio Sources J. A. Roberts ................................... 37 Polarization Studies of Discrete Radio Sources V. Radhakrishnan ............................... 53 N.R.L. Polarization Results C. H. Mayer .................................... 61 Recent Polarization Work at Jodrell Bank R. G. Conway .................................... 69 Linear Polarization of Discrete Radio Sources by Use of a 9.4 cm Maser W. K. Rose .................................... 75 Radio Properties of Identified Extragalactic Sources T. A. Matthews ................................. 79 OPTICAL OBSERVATIONS The Identification Problem R. Minkowski ................................... 87 Optical Properties of Radio Galaxies E. M. Burbidge ................................. 95 Optical Spectra of Radio Galaxies M. Schmidt .................................... 111 Quasi-Stellar Radio Sources T. A. Matthews ................................ 119 vi CONTENTS Page THEORY Mechanisms of Energy Generation in Extragalactic Radio Sources G. R. Burbidge .................................. 123 Collective Star Formation as a Contributor to Extragalactic Radio Sources A. G. W. Cameron .............................. 133 On the Interpretation of Faraday Rotation Effects Associated with Radio Sources B. J. Burn and D. W. Sciama ..................... 139 A Model of Radio Galaxies H. van der Laan ................................. 147 Dynamics of Magnetic Fields in Radio Sources L. Woltjer ..................................... 155 CONCLUDING REMARKS H. C. van de Hulst ................................ 163 INDEX ............................................ 167 Introduction On December 3 and 4, 1962, the Goddard Institute for Space Studies, an office of the National Aeronautics and Space Adminis- tration, was host to an international group of astronomers and physicists who met to discuss the physics of nonthermal radio sources. This was the third in a continuing series of interdisci- plinary meetings held at the Institute on topics which have a spe- cial bearing on the main lines of inquiry in the space program. The conference was organized by G. R. Burbidge of the University of California at San Diego and by L. Woltjer, then of the Univer- sity of Leiden but temporarily at the Massachusetts Institute of Technology, and now of Columbia University. Many nonthermal radio sources are of interest to astronomers, but only those outside the solar system were discussed at this conference. These latter sources comprise at least four types of object: supernova remnants within our galaxy, normal external galaxies, "radio galaxies," and certain objects which at that time were called "radio stars," but which are now known as "quasi- stellar radio sources." Objects in the last two categories are of particular interest to physicists because of their very large energy contents. It is a great challenge to determine how such vast quan- tities of energy can be generated in a short period of time and converted into the intense fluxes of relativistic electrons that are required to give the radio emission by the synchrotron process. The sun emits 4 × 10_3 ergs/sec over the entire spectrum. A typical supernova remnant has an emission rate of nearly the same order in the radio region alone. Further, there are unusual remnants, such as the Crab Nebula, which emit synchrotron radiation in the visible region at a rate which is an order of magnitude greater than the (thermal) solar value. A normal galaxy will emit about 104' ergs/sec of visible light and roughly 1034 ergs/sec in the radio region. The latter emission is believed to originate both in supernova remnants and in the general synchrotron radiation produced by fast electrons moving through the magnetic field structure of the object. But some galaxies (called "radio galaxies") are much stronger radio emitters. They produce 104°-1045 ergs/sec at radio frequencies. In these cases, the radio source frequently comprises two principal com- ponents, whose separation may be _10 '_ light years. Lower limits to the ages of the sources are thus implied, and one can deduce vii t viii INTRODUCTION that some of the most intense radio galaxies must have stored 10 '_l ergs in the magnetic field and high energy particles. The energy required is equivalent to the total conversion of 107 solar rest masses, and presumably is released in some event or series of events which occurs in the radio galaxy. However, there is no known process in which rest energy can be made totally available for such purposes. Thermonuclear reactions release about 1% of the rest energy, and it appears that probably only a few per cent of the rest energy of a massive collapsing star can go into a shock wave. Hence it appears that the actual matter involved in the violent processes which give rise to an intense radio galaxy must be of the order of 10 _ to 10 _ solar masses. Total galaxy masses are _ 101' to 101_ MQ. The puzzle of this large energy requirement was one of the principal motivations for the organization of the Dallas Sympo- sium on Gravitational Collapse and Other Topics in Relativistic Astrophysics, held in December, 1963. In the year between the conferences at the Goddard Institute and at Dallas, an immense amount of new observational material has been obtained regarding the quasi-stellar radio sources. In December, 1962, they were thought to be actual stars or supernova remnants, located in our own galaxy. By December, 1963, it had become virtually certain, however, that these objects are in fact located at extremely great distances. It had further been determined that these sources emit optically at a rate which far exceeds that of a galaxy, that their radio emission is comparable to that of the most intense radio galaxies, and that they occupy volumes which are very small compared to that o/ a galaxy. It may be that there is a continuous gradation of properties between the quasi-stellar sources and the intense radio galaxies. Because of the rapid obsolescence of the material presented on quasi-stellar radio sources at the Goddard Institute conference, it has been al- most completely omitted from this volume. Readers are referred to the forthcoming proceedings of the Dallas Symposium and to the references listed elsewhere in this volume, for more information on these objects. The papers in this book have been somewhat reorganized from their actual order of presentation at the Goddard Institute conference. Separate sections of radio observations, optical observations, and theory have been assembled, although there was some intermixture of the first two categories at the conference. It is evident that the immense strides which have been made in the un- derstanding of radio sources have depended upon optical iden- 4 • INTRODUCTION ix tifications of the radio objects, and these in turn have depended upon recent refinements in the determinations of the positions and structure of the radio sources, made possible by the use of large interferometers and (in a few cases) the lunar occultation tech- nique. It is important that radio and optical studies should con- tinue to be closely

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