A Brief Observational History of the Black

A Brief Observational History of the Black

Review Article

A Brief Observational History of the Black-Hole Spacetimes

Wolfgang Kundt

Argelander Institute of Bonn University, Auf dem H

ugel 71, 53121 Bonn, Germany

Correspondence should be addressed to Wolfgang Kundt; wkundt@astro.uni-bonn.de

Received 24 October 2014; Revised 17 December 2014; Accepted 18 December 2014

Academic Editor: Seyed H. Hendi

which permits unrestricted use, distribution, and reproductio

n in any medium, provided the original work is properly cited.

In this year (2015), black holes (BHs) celebrate their 100th birthday, if their birth is taken to be triggered by a handwritten letter

from Martin Schwarzschild to Albert Einstein, in connection with his newly found spherically symmetric vacuum solution.

1. Introduction

Black holes are brainchildren of Einstein-Hilbert’s General

Relativity Theory (GRT). They arose naturally as the non-

singular solutions describing the axially symmetric vacuum

far fields of the gravitational collapse of a sufficiently massive

(rotating) burnt-out star under its own weight and were

subsequently likewise taken seriously on superstellar mass

scales—at the centers of galaxies—as well as on distinctly sub-

stellar mass scales, as evaporating mountain-sized objects (in

mass) formed during earlier cosmic epochs. The (more) gen-

eral possibility of a (slightly) nonsymmetrical gravitational

collapse without a regular event horizon—known under the

name of “naked singularity”—was eliminated from consid-

eration by Roger Penrose’s postulate of “cosmic censorship”

(CC, [

]), with the plausible expectation that collapsing bod-

ies would always remove their nonfitting higher multipole

moments via gravitational radiation—strongly suggested by

the heroic work of Richard Price [

]—an expectation which

has meanwhile been proven unjustified [

]: BH spacetimes

form a subset of measure zero within the class of all collapse

scenarios.

Should we worry? I do not think so. Observations have

shownthatweliveinsideacomparativelyyoung(partof

the) Universe, with a significant fraction of its primordial

hydrogen yet unburnt (towards chemical elements of higher

nuclear binding energy). No BH has been reliably detected in

our cosmic neighbourhood. Quite likely, all we have to do to

save our regular physical description of this world is to replace

Penrose’s CC hypothesis by the slightly more restrictive one

of AUC (avoidance of unhalted collapse).

2. Birth and Growth of the Black Hole Idea

It was the problem of unhalted gravitational collapse of

large masses under their own weight, which emerged freshly

with Einstein’s GRT—in generalisation of Newton’s Theory—

because, in GRT, pressure has weight (like mass or energy),

and beyond certain (high) mass densities, pressures can no

longer halt a collapse. The most massive neutron stars are

close in density to the instability limit; they realise an extreme

stellar population. What happens when additional matter is

transferred to a heavy neutron star? This question opened the

doors to BH favouritism.

This question is serious, but it is not fatal. Stars can

lose mass through centrifugal ejection, through their winds,

through their radiation, and through nuclear detonations, as

novae—also through supernova explosions—and within the

large set of known neutron stars, none so far is close in mass

to its stability limit of 3

푀

⊙

;theyallhavemasses

≲

푀

⊙

.We

realise that there are hurdles to BH formation.

BHresearchhasnotbeeneasy,asitrequired,among

others, explicit analytic solutions of the GRT equations and

their complete analytic extensions from local to global ones;

see the careful survey by Heusler [

] and also Kundt [

–

]

and Thorne [

]. For a few years after their discovery, all of

usworldwidewerereadytobelievethatBHsmightturnout

to be standard building blocks of the Universe. But it was

equally clear to us, individually as well as in international

discussion groups, for several years, that their detection in

theskywouldbefarfromeasy.Becauseeventheirradiation

cannot escape from them; they cannot emit signals, or blow

winds, or (even) eject jets; they can only swallow, not spit,

Hindawi Publishing Corporation

Advances in Mathematical Physics

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Advances in Mathematical Physics

and only absorb, not emit. Their detections would have to

be rather indirect, by carefully watching their surroundings

at the right moments, at low signal strengths, because of

escaping from near the bottom of a deep potential well. As

concerns jets from BHs, supportive claims have been made in

recent years, without proof and without reference to a proof,

basedonlyonimaginationandspeculation.Established

jet engines are among the most sophisticated machines of

the inorganic Universe; they involve strong, heavy rotating

magnets and stable de Laval nozzles [

]. For years, our

best candidate for BH detection has been Cyg X-1, an X-

ray binary blowing jets intermittently containing a bright

primary star and an unseen, heavy companion [

–

]: quite

likely, the unseen companion is a neutron star surrounded

by a massive accretion disk [

]. None of the rich classes

of stellar-mass BH candidates has ultimately turned out to

contain a BH [

]; our search had been in vain.

Another class of BH candidates was already proposed

in [

] by Donald Lynden-Bell, through the fear that super-

massive black holes, SMBHs, could form near the massive

center of the deep potential well of a large galaxy. How can

suchaccumulatedmatterbeejectedagaintolargedistances

of lower gravity? A special conference at Bad Honnef in

1995, cochaired by Peter Scheuer, gave a tentative answer to

this puzzle: the central galactic disks may well be supported

by ordinary plasma pressure (perpendicular to disk plane)

combined—in radial direction—with centrifugal forces, and

their nuclear-burning matter may well be reejected into the

CGM in the shape of fountains of galactic scale, observed

as an active galaxy’s

burning disk

(BD), broad-line region

(BLR), NLR, ELR, and EER, out to

Kpc from its center

and beyond, with the required power supplied by nuclear

burning, in combination with conserved angular momentum

fromthepastspiral-inmotionthroughthedisk[

]. This

interpretation has meanwhile been corroborated by the SDSS

plot of the core masses of

≲

15000 galaxies [

], whose masses

decrease with cosmic time, from some

9.5

푀

⊙

푧 ≈ 4.5

down to some

6.5

푀

⊙

at present, as well as by the two halo-

sized

훾

-ray lobes of our Milky Way mapped by the FERMI

mission, which are fed in the vicinity of Sgr A

∗

,thehardpoint

source at our galactic center [

]. Already Victor Ambart-

sumian noted in [

] that galactic centers are observed to

eject, rather than to swallow. And in [

] I argue that all the

activities near Sgr A

∗

are satisfactorily described by a BD,

whilst they are multiply inconsistent with a SMBH in its place.

3. Black Hole Thermodynamics and

the (

≥

4) Classes of Black Holes

Once the BH spacetimes had been mastered mathemat-

ically—culminating with Roy Kerr’s metric for a rotating BH

in 1963—and once the expected stellar-mass BHs and the

likewise expected supermassive BHs in the galactic centers

hadbeenbaptised—in1971—byJohnA.WheelerandRemo

RuffiniinPrinceton,backedupbyStephenHawkingetal.

in England’s Cambridge, it was a must to extend their

considered mass range to the maximal physically expected

one and to reflect on the specific properties of the subclasses:

at this point, Stephen Hawking [

]tooktheworld’slead,

by opening the chapter “BH Thermodynamics,” at the seventh

Texas Symposium on Relativistic Astrophysics in Dallas,

a few days before Christmas 1974. He proposed a (mass-

independent) marriage of GR and quantum mechanics, by

assigning a de Broglie wavelength

휆

of the order of its

horizon length to a BH of mass

푀

and with it a temperature

푇:=ℏ푐/휆푘

,suchthataBHofmass

푀

has a temperature

푇(푀) ≈ 10

−7

푀

⊙

/푀

.Obviously,thisquantumtempera-

ture is ignorably small for BHs of stellar mass or bigger but

could lead to detectable cosmic explosions for mountain-

sizedBHs,whentheyshrinkdownbyevaporationtothe

Hawking mass

푀

퐻

=ℏ푐/퐺푚

휋

=10

g(with

푚

휋

mass

of the pion).

Instead of the hundreds of publications in this wide

theoretical field, may I just list the names of a few of its leading

authors. Beyond those already quoted, they are Brandon

Carter, Werner Israel, Ted Newman, David Robinson, Jim

Bardeen, Martin Rees, Jim Hartle, Jacob Bekenstein, and

Robert Wald. Their considerations have led to a classification

of all possible BHs into

mini

midi

,and

maxi

ones, each class

ranging in mass through a factor of

√

ℏ푐/퐺푚

휋

≈10

,starting

at the bottom with the Planck mass

푀

√

ℏ푐/퐺=10

−5

g—

whose Compton wavelength equals its Hawking

wavelength—and extending up to the mass of the observable

universe,

푀

푈

= (ℏ푐/퐺)

/푚

휋

=10

g. As concerns their

detection, midi BHs have only been considered seriously

once in 1974, as a possible explanation for the 1908 Tunguska

catastrophe, even though no mechanism for their formation

hadeverbeenproposed.TheywererefutedbyBeasleyand

Tinsley [

], based on an absence of tsunamis in the Pacific

duringthedaysofthatevent(whichwouldhavebeenraised

by the midi BH during its exit from the ocean, after having

crossed the Earth). Note that in my understanding, the

Tunguska event has not been an infall event from outside,

rather an ejection event from inside, a kimberlite [

Next, explosions of mini BHs have been ruled out by Joe

Taylor by a large margin, via an absence of detected radio

bursts of the implied kind. And I have never been shown

convincing evidence of a maxi BH either, throughout the

decades since their proposition [

]. Note that yet another

class of BHs has been taken seriously in 2012, when CERN’s

LargeHadronColliderwasassignedtosearchfortheHiggs

particle, quantum mini BHs, much lighter than the Planck

mass, whose growth was feared to possibly swallow the whole

city of Geneva. Fortunately for our home planet Earth, this

most dangerous class of BHs has not shown up either.

BHs have thus remained unobserved objects in all weight

classes. Even worse, the book by Yvan Leblanc [

]claimsthat

BH thermodynamics is inconsistent with standard textbooks

onphysics.Anumberoffurtherpeoplesupporthisview,

amongthemVladimirBelinski[

]. The publication of my

own reply to Hawking’s launching paper [

]onBHentropy,

in [1976], was delayed by more than half a year and eventually

printed without sending me proof sheets and with 13 typos

added. In it, I pointed out that his definition of BH entropy

was inconsistent with the textbook definition of entropy

in physics. (Textbook entropy scales linearly with mass,

página 3

Avanços na Física Matemática

A entropia de Hawking escala-a quadraticamente.)

propostas para combinar GR com mecânica quântica, minha própria

compreensão é que a teoria quântica não deve ser aplicada

para sistemas cujas partículas são puramente macroscópicas, que

é muito maior que seu comprimento de onda de Broglie. este

critério abrange também a recente proposta de Vaz [

4. Deve a censura cósmica ser substituída por

a hipótese da AUC?

As singularidades nuas eram antipáticas desde o começo de

História de BH, em particular por Penrose [

], e nunca

apelou para astrofísicos, porque a sua relevância seria

significa que nos falta uma teoria completa do espaço e do tempo. E se

geodésicas nulas futuras poderiam conectar subsistemas em colapso de

o Universo com nossos telescópios, isso significaria que estes

subsistemas - ou pelo menos certas partes deles - não podem mais

ser descrito por soluções regulares de GRT, isto é, que

falta uma teoria completa do nosso mundo. Mas o trabalho de Pankaj

Joshi [

], Hernando Quevedo, Bahram Mashhoon, Pankaj

Joshi e Malafarina [

], e alguns outros

o colapso gravitacional geral termina em singularidades nuas,

em vez de em BHs. Que escolha temos?

Até agora, nenhum lugar no céu jamais me pareceu

contendo uma singularidade nua. Com cuidado suficiente, todos os nossos

mapas sempre permitiram interpretações por não-singulares

condensações de matéria, não muito diferentes da nossa energia solar

sistema. Mas claramente, se a maior parte do hidrogênio cósmico fosse

substituído por ferro, ou justo por

os que estão acima não previam mais obstáculos para evitar

colapso inalterado, tanto na massa estelar como na superstelar

balanças expostas.

discos centrais de galáxias seriam espremidos fora do equilíbrio

pelo seu próprio peso, quase todos eles se formando nus

singularidades, dificilmente qualquer um deles formando um buraco negro. o

fato de que nada disso foi observado até agora me faz

otimista em acreditar que a nossa vizinhança cósmica é (ainda)

longe desse Estado, que será o maior subdomínio

o universo para que possa substituir a hipótese de Roger

pela AUC, a hipótese de um

evitar o colapso inalterado

[

]. AUC postula que em nosso cósmico atualmente observável

vizinhança, colapso gravitacional não

acontecer.

Tal colapso inalterado pode ser evitado pelos obstáculos

de queima nuclear, de momento angular conservado, de

pressões estabilizadoras e / ou pressões magnéticas, e

de ejecções semelhantes a jactos, que podem atrasar um colapso. Estrela

a formação é atrasada para (apenas) alguns

푀

⊙

/ ano em nosso presente

galáxia, colapsos estelares são interrompidos pela queima nuclear ou,

durante os estágios posteriores, por pressões de degeneração dentro do

estrelas, também por explosões Nova e SN, e centros galácticos

canlikewisebesupported contra o colapso por suas pressões,

por aquecimento nuclear, e por ejeções explosivas de seus

discos centrais que atrasam o seu encolhimento final até depois

a vida do nosso sistema solar.

Muito provavelmente, não precisamos nos preocupar com a

futuro da vida terrestre. É melhor nos concentrarmos em proteger

levando o nosso planeta Terra contra os perigos da falta de

crescimento populacional, de catástrofes nucleares, de resíduos

queima nuclear e de pragas. Eles são muito mais para ser

temido do que a morte final de estrelas distantes e de distante

galáxias no Universo.

Conflito de interesses

O autor declara que não há conflito de interesses

sobre a publicação deste artigo.

Agradecimentos

Meus cordiais agradecimentos pelo papel - incluindo seu conteúdo -

vá para Ole Marggraf e também para Hans Baumann. Obrigado

como uma referência anônima em cinco

melhorias do papel original.

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38-46, 1972.

[2] RHPrice, “Perurburbações não-esféricas de gravidezes relativísticas

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[8] W.Kundt, “SchwarzeL

ochernachwievoraktuell ”,

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Natureza

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[10] KS Thorne, "A busca por buracos negros"

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Estrêla de Neutróns?"

Natureza

vol.247, no.5440, pp.351-352,1974.

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de binários de raios-X ”,

O Jornal Astrofísico

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Avanços na Física Matemática

[16] AWShafter, RJHarms, B.Margon eJ.I.Katz, “Alower

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Cygnus X-1 ”

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[28] Y. Leblanc,

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, eField-

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[30] C. Vaz, "Não há nada" preto "sobre um buraco negro"

http: // xxx

.tau.ac.il / abs / 1407.3823v1

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Uma breve história observacional dos espaços-tempos Black-Hole. Available from: https://www.researchgate.net/publication/272370922_A_Brief_Observational_History_of_the_Black-Hole_Spacetimes [accessed Mar 26 2018].