Astrophysics: A New Approach, Second Edition (Astronomy and Astrophysics Library)

237 Pages·2004·3.41 MB·English

by  Wolfgang Kundt

ASTRONOMY AND
ASTROPHYSICS LIBRARY
SeriesEditors: I.Appenzeller,Heidelberg,Germany
G.Bo¨rner,Garching,Germany
A.Burkert,Mu¨nchen,Germany
M.A.Dopita,Canberra,Australia
A.Eckart,Ko¨ln,Germany
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R.Kippenhahn,Go¨ttingen,Germany
J.Lequeux,Paris,France
A.Maeder,Sauverny,Switzerland
V.Trimble,CollegePark,MD,andIrvine,CA,USA
Wolfgang Kundt
Astrophysics
A New Approach
With48Figures,Including16 Color Plates
123
ProfessorDr.WolfgangKundt
Institutfu¨rAstrophysik
Universita¨tBonn
AufdemHu¨gel71
53121Bonn,Germany
E-mail:[email protected]
Coverpicture:Theradiogalaxy0756+272of(Eilek)typeB,or‘tailedsource’,whosejetheads–orstagnation
surfaces-arethoughttonolongerploughsupersonicallyintotheirambientmedium.ThegalaxybelongstoAbell610.
Ithasaredshiftofz=0.0956;itsradiolobeshaveanangulardiameterof160".Itsjetsubstanceisthoughttobepair
plasmaperforminganE(cid:1)×B(cid:1)-drift.TheAGNissome0.7cmtotherightofthebright(red-cored)centralhotspot.
[ImagecourtesyofFrazerOwen,NRAO/AUI]
ISSN0941-7834
ISBN3-540-22346-0SecondEditionSpringerBerlinHeidelbergNewYork
ISBN3-540-41748-6FirstEditionSpringerBerlinHeidelbergNewYork
LibraryofCongressControlNumber:2004109321
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Preface to the Second Edition
When the first edition of this book began running out, less than two years
after its appearance, Springer informed me that I should concentrate on a
second,somewhatenlargededition.Ilikedthatofferbecausemypersonalcopy
aboundedwithnotesinthemargin:omissions,misformulations,incomingnew
results, typos, and an insufficient index. In particular, when engaging myself
innewproblems,Ihadnoticedmissingformulae,andmissingsections.During
the months of updating, it has been satisfying to see one gap after the other
close.
But I noticed still something else, when reading the news of the week in
Nature, Science, Skyweek, in freshly written reviews, and in talks. A certain
setofdisagreementsintensified,betweencommonwisdomandwhatIconsider
itspreferredinterpretations.Everynew‘hostgalaxy’ofanother‘cosmological
γ-rayburst’ lookstome like anotherlightecho froma nearbyGalactic reflec-
tion nebula, with no supernova involved, every flaring jet source like another
monoenergetic pair-plasma beam ramming into a heavy obstacle, and every
ms-pulsarlike the neutron-starremnantofa weaklycoupled core-collapsesu-
pernova. ‘Alternative’ interpretations like these have evolved throughout my
career, starting in 1975, and had grown in number to 79 when I reached re-
tirement age in 1996. Meanwhile, they have accumulated to 100. Almost one
thirdofthemhavemeanwhilearrivedatindependentlyinpublishedliterature
by other scientists, hence they are unlikely to be all very misleading. I have
thereforeupdatedthem,andaddedthemtothisbook,atitsend,tostimulate
the seriousreader.AsrepeatedlyexpressedbyRichardFeynman, wemustal-
ways be prepared, in astrophysics much more so than in laboratory physics,
to revise our knowledge [Robbins,1999].
The preface to the first edition contains a list of former collaborators,
students, and friends who have helped me reach the present insight. This
secondeditionhasstillprofitedfromseveralofthem,withitsfinalstagesmost
strongly influenced by Gernot Thuma and by Christoph Hillemanns. Eleven
additional figures have been converted into eps files by Christof Wenta, and
regular help with the electronic data handling has again been received from
Gu¨nter Lay, and occasionally from Ole Marggraf;they all deserve my sincere
thanks.
Bonn, April 2004 Wolfgang Kundt

Preface to the First Edition
ThisbookisbasedonaclassthatIlectured repeatedlyduringthe years1986
through 1999, at Boston, Bangalore, Bonn, Siegen, and Linz. Occasionally I
lectured it within two or more terms. In each case, it was my endeavour to
providemy audience with as complete as possible an overviewof the physical
methods and results used in present-day astrophysics, in order to gain an
insight into the functioning of the Universe.
Here the true climax of cosmic insight appears to me to be the Anthropic
Principle, whose strongest variant reads: The state parameters, and laws of
physics are such that after a suitable interval of time – of the order of 10
Gyr,(Gyr :=109yr)–abiosystemcanevolveonasuitableplanetormoon of
a suitable star or planet, with e.g. Homo Sapiens as a sensing observer. I.e.
the functioning of our animated (!) planet Earth cannot only be described in
physicalterms, but its existence dictates, indirectly, the structure of the laws
of physics. Thus, you and I would not exist, for example, if the mean cosmic
substratum was (only) some 102-times denser than it is: The Universe would
haverecollapsedbeforehigherterrestriallifecouldevolve.Thebiologicalclock
is tuned both to the solar clock, and to the cosmic clock.
But Earth does not seem to take an outstanding part in the Universe; it
obeys the same laws. Time and again, the Copernican Principle can serve
as a useful guide: We live on a typical planet which moves around a typical
star inside a typical (spiral) galaxy inside a typical cluster of galaxies, and
which has been endowed with life for a typical cosmic era. Admittedly, we
play a considerable role in what happens in the near vicinity of Earth – by
our technical achievements and mental insight – but we do not really play
a role that would upset the Universe. We are rare, but not central, and not
forbidden.
Astrophysics is not exactly a subfield of physics, but an extension of
physics: It concerns itself with material objects on much larger (than ter-
restrial) length scales, whose substratum has in general much lower densi-
ties, and exerts much lower pressures, though occasionally also much higher
ones, whose temperatures, magnetic fields, electric voltages, and velocities
VIII Preface to theFirst Edition
have much larger ranges than on Earth. Often we have to extrapolate our
knowledge.Suchextrapolationsinvolvenaturaluncertainties,asdotheprecise
localcircumstancesofanobservedobjectwhichingeneralcannotberetrieved
reliably from its observations. We must therefore be careful with our inter-
pretations, more careful than textbook knowledge occasionally is: subjunctive
moods cannot be avoided by a trustworthy description.
I shall stress such possible weak spots in our insight, candidates for the
subjunctive mood, wherever they occur to me, in order to help prevent re-
search from getting stuck in dead ends. The existence of such weak spots is
shared with all exact sciences whose theories are not immediately testable
– like geophysics – whenever processes run in the Earth’s unaccessibly deep
interior, or unnoticeably slowly, as in volcanism, and plate tectonics – or bio-
physics – whenever objects of interest are submicroscopically small so that
their perturbation-free recording in vivo is difficult, such as the sub-cellular
waterpumps inthe endodermalwallsofroottips.Theyhaveoften ledto vio-
lent,loudormutecontroversies(betweenindividualsand/orschools),without
any real necessity: The evolution of insight would probably fare better with-
out scientific revolutions if alternative interpretations were considered legiti-
mate, and were always mentioned, as has been repeatedly emphasized, e.g.,
by Richard Feynman.
This book summarizes a significant fraction of my life’s work, and owes
its existence to decades of weekly seminars and talks whose participants and
speakershelpedinshapingmyinsight.AmongthemaremyHamburg‘master’
Pascual Jordan and co-students Ju¨rgen Ehlers and Klaus Hasselmann, my
Bonn ‘patron’ Wolf Priester, as well as my successive associates, students
and friends Hans Heintzmann, Eckhard Krotscheck, Max Camenzind, Hajo
Leschke,MarkoRobnik, AxelJessner,Ashok Singal,Reinhold Schaaf,Daniel
Fischer, Hsiang-Kuang Chang, Carsten van de Bruck, Hans Baumann, and
GernotThuma.StefanWagnerhelpedwithstate-of-the-artspectra.Reinhard
Schlickeisertriggeredoff the introductorylectures which have materializedin
this book. To all of them go my hearty thanks. During the 18 months of
preparationandworkonthisbook,MarkusDraxlerintroducedmeknowingly
and patiently to the use of the routine Scientific WorkPlace, and Gu¨nter
Lay and Horst Scherer followed him up masterfully. Stefan Siegel converted
the numerous paper drawings into printable eps files, and Vadim Volkov and
Martin Hetzer proofread the chapter on Astrobiology. Again, my thanks to
all of them!
Bonn, July 2001 Wolfgang Kundt
Contents
Useful Numbers ...............................................XIII
1 Cosmic Structures ......................................... 1
1.1 Calculus and Notation ................................... 1
1.2 Solar System............................................ 3
1.3 The Milky Way ......................................... 7
1.4 World Substratum....................................... 17
1.5 Distance Ladder......................................... 19
1.6 Galaxies, Clusters of Galaxies, IGM, and Sponge Structure ... 22
1.7 Cosmology ............................................. 24
2 Gas Dynamics ............................................. 29
2.1 Galactic Pressures....................................... 29
2.2 Shock Waves............................................ 32
2.3 Stellar Winds ........................................... 34
2.4 HII Regions............................................. 35
2.5 Stability of a Contact Discontinuity........................ 36
2.6 Pressure Bombs ......................................... 37
2.7 Supernovae ............................................. 38
3 Radiation and Spectra..................................... 45
3.1 Radiation by an Accelerated Point Charge.................. 45
3.2 Frequency Distributions of Single Emitters.................. 48
3.3 Spectra Emitted by Ensembles ............................ 54
4 Thermal Processes......................................... 61
4.1 Entropy Balance and Cooling ............................. 61
4.2 Thermal Equilibria ...................................... 65