Mini-course of lectures at Verão Quântico Ubu, Espírito Santo, Brazil, 17 to 22 February 2019,

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2 Mini-course of lectures at Verão Quântico 2019 Ubu, Espírito Santo, Brazil, 17 to 22 February 2019,

3 Black-Physics-Valeri- Frolov/dp/

4 PDF file of the book can be found at (search for frolov novikov )

5 At: BLACK HOLE 913,000,000 NEUTRON STAR 23,800,000 In virtual reality black hole are more `real than neutron stars.

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8 Two predictions of the Einstein's General Relativity (1915) Gravitational waves Black holes One hundred years later... The first observing run (O1) of Advanced LIGO was scheduled to start 9 am GMT (10 am BST), 14 September Both gravitational-wave detectors were running fine, but there were few a extra things the calibration team wanted to do and not all the automated analysis had been set up, so it was decided to postpone the start of the run until 18 September. No-one told the Universe. At 9:50 am, 14 September there was an event.

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10 3 Dec The LIGO Scientific Collaboration and the Virgo Collaboration have released the results of their search for stellar-mass coalescing compact binaries during the first and second observing runs using an advanced gravitational-wave detector network. This includes the confident detection of ten binary black hole mergers and one binary neutron star merger. 4 new events. The "most massive case" GW Its source is made up of black holes with masses 50 M and 34 M.

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13 Facts about GW Masses 35M and 30M. Final mass 62M, 3M was emitted in the form of gravitational waves. This 49 is about 5% of the total mass watts 50 times greater than the combined power of all light radiated by all the stars in the observable universe. It was observed about 8 cycles from 35 Hz to 250 Hz. 80 Total number of emitted gravitons 10.

14 Gravitational waves G G 2 Metric perturbation g = + h, h Q, E ( Q), 4 5 rc c MR MR Q MR, Q, Q. 2 3 T T R 2 R GM Third law of Kepler: GM, T, Q, 2 T GM R h G M Rg R Rg Rg =, E 4 r Rc R r R r R g 5 c G R 5

15 5 c R R erg / s. If we put 1 / 4, then ( ) 10 G R R 59 g g E erg / s = watt 50 times greater than the combined power of all light radiated by all the stars in the observable universe. This event happened at the distance r 400mpc light years, r cm. The grav. radius of 60M Rg 60 3km = cm, h

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17 Gravitational collapse will always occur on any star core over 3-5 solar masses, inevitably producing a black hole. Approximately 1/3 of the star systems in the Milky Way are binary or multiple. The rest 2/3 are single stars. A heavier companion in the stellar binary has faster evolution than the lighter one. If the mass of the heavy star is large enough a system may become a black hole binary.

18 Known candidates for stellar mass black holes were discovered in such systems. The motion of a star companion in the binary can be detected. This gives information about the mass of the black hole candidate. Estimates give : the number of stellar mass black holes in our Galaxy is about A similar 8 9 or larger number of neutron stars exist in the Gal axy.

19 Indirect methods of seach for stellar mass black holes X-ray object in a binary system, Its mass measuring by means of Newton's law, Existence of an accretion disk, Velocity of matter at the : Broading of Fe lines, ISCO Total brightness of the accretion disk.

20 Schwarzschild BH: r = 3r = 6M ISCO E ISCO g / m= 8/ 9 BH efficiency: 5.72% Extremal Kerr B r ISCO E ISCO = M / m = 1/ 3 2 H (J/M =1): BH efficiency: 42.36%

21 Stellar-mass black holes with (Super)massive black holes with Intermediate-mass black holes with Primordial black holes with mass up to Micro black holes M 3 60M M M 3 10 M M M M M Planck 5 9 M M Planck c = 10 G 5 g The quantum gravity effects become important for black holes with M M Planck. The black holes of smaller mass do not exist, at least in the standard classical sense.

22 Supermassive black holes BH in the center of our Galaxy, Milky Way. Sagittarius A* 6 is the location of a supermassive black hole of mass 410 M. SMBHs in the center of other galaxies.

23 A black hole is a compact massive object, the gravitational field of which is so strong that nothing (even the light) can escape from it. The boundary of the black hole, called the event horizon, is a surface at which the escape velocity is equal to the velocity of light. 1 2 mv 2 = GMm R R g = 2GM c 2

24 John Archibald Wheeler ( ) The name "black hole" was invented in December 1967 by John Archibald Wheeler. Before Wheeler, these objects were often referred to as "black stars or "frozen stars".

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26 Event horizon (BH boundary) is almost everywhere null surface Black hole surface topology is. Its surface area never decreases (EC) Soon after their formation black holes become stationary (the `balding phase T r / c ). Stationary black holes are either static (Schwarzschild) or axially symmetric (Kerr). S g 2

27 Uniqueness theorem: Stationary isolated BHs are uniquely specified by their mass and angular momentum and are described by the Kerr metric. The Kerr metric besides the evident ST symmetries has also hidden symmetry. Geodesic equation of motion are completely integrable. Massless field equations allow the separation of variables. Black holes are classically stable.

28 The radius =2M is known as the gravitational radius or the Schwarzschild radius. In physical units, after restoring G and c constants, it has the value r = 2GM c S rs 2 rs ds = 1 dt + 1 dr + r d r r describes the gravitational field in vacuum, outside a spherical distribution of matter. This matter may be either static or have radial motion preserving the spherical symmetry. According to Birkhoff's theorem, the external metric does not depend on such motion. In the absence of matter, the metric describes an exterior of a spherically symmetric static black hole. In this case r S is the radius of its event horizon.

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30 ds dt + d + r d S

31 The equation U = -V determines a three-dimensional spacelike slice of the Kruskal spacetime. This slice passes through the bifurcation surface of the horizons. It has two branches. This subspace is called the Einstein-Rosen bridge. Its internal geometry dr dl r d dl 1 2Mr = + = 0 r 2 = (1 + M2 ) M = 1+ 2 dl = d + ( d + sin d ) = 2 The geometry of a two-dimensional section of the metric can be embedded in a at three-dimensional space as a revolution surface

32 where dl = dz + dr + r d = dr (1 + z ) + r d z = 2 2 M ( r 2 M )

33 Sandro Botticelli (1480) La Carte de l'enfer ( The Abyss of Hell ). An illustration to Dante s The Divine Comedy

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36 In the `physical' spacetime the signature of the metric is ( - ; + ; + ; + ). The Schwarzschild metric is static and it allows an analytical continuation to the Euclidean one ( + ; + ; + ; + ). This continuation can be obtained by making the Wick's rotation t = it E. The corresponding space, called a Euclidean black hole, has interesting mathematical properties and has important physical applications. The two-dimensional part of the Euclidean metric d = g dt E E dr g 2 Near the Euclidean horizon is has the form d dt + d E E In a general case this metric has a conical singularity. This singularity vanishes if is a periodic coordinate with the period t E 2 0 t E

37 Consider the (t-r)-sector of the Schwarzschild metric dr 2 2 ds = g dt + + r d g 2M g = 1 r 2 d In the vicinity of the horizon: r = r (1 + y) y 1 S the proper length distance from the horizon = r r S dr g 2r S y

38 d = dt + d = 1 (2 r ) = 1 (4 M) is the surface gravity of the black hole. S ds dt + d + r d S Regularity at =0 requires t is periodic with a period 2 /. This condition determines Hawking themperature = H E 3 c 8 Gk M B.

39 Why = H 3 c 8 Gk M B enters the expression for the temperature? We keep in the relations, but put c= G = 1 E 2 8 M We used here that is equal to the period of the Euclidean time..

40 This regular four dimensional Euclidean space is called the Euclidean black hole or the Gibbons-Hawking instanton. The inverse period in Euclidean time is equal = H 2 is called the Hawking temperature of the black hole.

41 Rotating black holes

42 4D Kerr-NUT-(A)dS Derivation in 3 Simple Steps Step 1: Write flat ST metric in ellipsoidal coordinates ds 2 = dt 2 + dx 2 + dy 2 + dz X = r + a sin cos, Y = r + a sin sin, Z = rcos, = 1 X + Y Z r + a r dr ds = dt + ( r + a cos ) ( + d ) r + a ( r + a ) sin d

43 Step 2: Rewrite this metric in `algebraic form = cos, =, = 1 y a t a a r y ds = ( d + y d ) + ( d r d ) r + y r + y dr dy + ( r + y )[ + ], r = r + a, y = a y r y (i) Coefficients are rational functions; (ii) `Almost symmetric form

44 Step 3: Use this form of the metric to solve Einstein equations Assume that = ( r) and = ( y) and solve the equation R = 3 g ( =- /3) r r y y r Y( y) ds = ( d + y d ) + ( d r d ) r + y r + y dr dy + ( r + y )[ + ] r y [Carter 1968]

45 'Trace equation' gives: y 2 r r y y + = r + 12 ( ), r r y y = = 12 r c, 12 y c, c = r 2 r r r, c = y 2 y y r

46 The other equations fix some constants and we have = ( r + a )(1 + r ) 2 Mr, r = ( a y )(1 y ) + 2Ny y a rotation parameter, M mass, N `NUT' parameter, `cosmological term'

47 If we put = N = 0 and change coordinates 1 y = a cos, = t a, = a, we obtain Kerr solution in standard Boyer- Lindquist coordinates ( tr,,, ).

48 Mr 2 4Mrasin Asin 2 ds = 1 dt dt d+ d + dr2+ d = r + a cos = r 2Mr + a A r a a = ( + ) sin

49 The event horizon is located at Which are the roots of the equation The event horizon of the Kerr spacetime is a null 3-dimensional surface. Its spatial slices have the geometry of a 2-dimensional distorted sphere. The rotating black holes exist only for a M a M For the Kerr solution does not have a horizon and it describes a naked singularity. It is generally believed that such a singularity does not arise in real physical processes. r r r M M a ( r) = = + =

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51 Metric g is a trivial example of the Killing tensor. Kerr metric has 2 Killing vectors and. t Carter (1968) found that it also has a Killing tensor. This gives 4 integral of motion and make particle and light equations completely integrable.

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53 Angular momentum in Higher Dimensions ( D= 2 n+ ) J J J Jn i =, Ji = ji 0 j

54 5D vac. stationary black holes

55 (1) No Uniquness Theorem: For given M and J more than one BH solution (2) Complete integrability and separation of variables are generic properties of HD analogues of Kerr BH ( hidden symmetry generators V. F & D. K. 07) (3) Stability of HD BHs?

56 Main Results In the most general ( Kerr NUT ( A) ds) higher dimensional black hole spacetime : (1) Geodesic motion is completely integrable. (2) Hamilton Jacobi and Klein Gordon equa tions allow the complete separation of variables

57 Motivations Separation of variables allows one to reduce a physical problem to a simpler one in which physical quantities depend on less number of variables. In case of complete separability original partial differential equations reduce to a set of ordinary differential equations Separation of variables in the Kerr metric is used for study: (1) Black hole stability (2) Particle and field propagation (3) Quasinormal modes (4) Hawking radiation

58 Main lesson: Properties of higher dimensional rotating BHs and the 4D Kerr metric are very similar. HDBHs give a new wide class of completely integrable systems

59 "General Kerr-NUT-AdS metrics in all dimensions, Chen, Lü and Pope, Class. Quant. Grav. 23, 5323 (2006). n = D / 2, D = 2n + R = ( D 1) g, M mass, a ( n 1 + ) rotation parameters, k M ( n 1 ) ` NUT ' parameters Total # of parameters is D

60 Generator of Symmetries PRINCIPLE CONFORMAL KY TENSOR 2-form [ ] with the following properties: (i) Non-degenerate (maximal matrix rank) (ii) Closed dh = 0 (iii) Conformal KY tensor h g g, 1 b h c ab ca b cb a a D 1 ba a h = = is a primary Killing vector

61 All Kerr-NUT-AdS metrics possess a PRINCIPLE CONFORMAL KY TENSOR (V.F.&Kubiznak 07)

62 Uniqueness Theorem A solution of Einstein equations with the cosmological constant which possess a PRINCIPLE CONFORMAL KY TENSOR is a Kerr-NUT-AdS metric (Houri,Oota&Yasui 07 09; Krtous, V.F..&Kubiznak 08;)

63 4D Kerr metric example Principal CCKY tensor h = db 1 b= [ ( y 2 r 2 ) d r 2 y 2 d] 2 H = h h ; det( H ) = 0, = y 2, = r 2 + Lesson: Essential coordinates ( r, y), Killing coordinates (, )

64 Killing-Yano Tower CCKY : ( j) h h = h h... h j times KY tensors: k ( j) = * h ( j) Killing tensors: ( j) K = k k ( j) ( j) Primary Killing vector: a 1 D 1 = b h ba Secondary Killing vectors: j = K j

65 Total number of conserved quantities: ( n+ ) + ( n 1) + 1= 2n + = D KV KT g The integrals of motion are functionally independent and in involution. The geodesic equations in the Kerr-NUT -AdS ST are completely integrable.

66 Separation of variables in HD Black Holes

67 In D = 2 n + dimensional ST the Principal CKY tensor (as operator) has n 2D eigenspaces with eigenvalues x a. They can be used as coordinates. D canonical coordinates: n and n + Killing coordinates essential coordinates x j. a Complete separability takes place in these canonical coordinate s.

68 Hamilton-Jacobi ( S) = WKB ~ exp( is) m Klein-Gordon ( m ) = 0 "Dirac eqn= KG eqn " Dirac equation ( + m) = 0

69 Recent results Complete separability of Maxwell equations in 4 and higher dimensional spacetime in the off-shell generalized Kerr-NUT-(A)dS metrics [Lunin (2017, FKK (2017); Complete separability of massive field equations in 4 and higher dimensional spacetime in the off-shell generalized Kerr-NUT-(A)dS metrics [FKK (2017)];

70 "Black holes, hidden symmetries, and complete integrability", VF,Pavel Krtous and David Kubiznak. Living Rev.Rel no.1, 6 (195 pp.); arxiv: ( )

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72 Denote by q `charge' of the particle of mass m and by the field strength. Probability= m 2 exp( / m ) ( 2 ), P l q l mc = / mc is the Compton length and l is a separation of particles when they become `real'. P 2 3 mc 2 exp( ) q Static electric field: q = e, = E 2 3 mc P exp( ) (Schwinger, ) ee

73 c In gravity: q= m, = =, 4GM P = H mc mc exp( ) = exp( ), c GkM H 4

74 Order of magnitude estimation E 2 2 [ m][ L] [ m][ L] [ E], [ ], c r 2 S 2 3 [ T] [ T]. This relation is valid in any number of dimensions.

75 Barvinsky, V.F., Zelnikov, Wavefunction of a Black Hole and the Dynamical Origin of Entropy, Phys.Rev. D51, 1741 (1995)

76 This regular four dimensional Euclidean space is called the Euclidean black hole or the Gibbons-Hawking instanton. The inverse period in Euclidean time is equal = H 2 is called the Hawking temperature of the black hole.

77 is a wavefunction of (free) quantum field ˆ. ( x) = ( t = 0, x) ˆ ( t = 0, x) ( x) = ( x) ( x) ( x) = ( ( x))

78 ( x) = ( x) + ( y) + ( ( x), ( y) ) + ( y) + ( x) ( y) + ( x)

79 = 1 ( ( x), ( y) ) Z + [ D (, x)]exp( SE ( )) BC BC: = (0, y) = ( y), = ( 0, x) = ( x) + + Statement: So defined ground state wavefunction coinsides with Hartle-Hawking vacuum in the eternal black hole. ["Wavefunction of a Black Hole and the Dynamical Origin of Entropy" ( ) Barvinsky,V.F., Zelnikov, Phys.Rev. D ] Z 1 Tr + + ˆ = ( ) Density matrix

80 ( ( x), ( x ')) [ D ( y)] ( ( x), ( y) ) ( ( y), ( x '))

81 ( x) ( x ') + ( x') 1 ( + ( x), + ( x ')) = Z [ D] exp( SE[ ]) ( x) + [ ] exp( [ ]) Z D S E =

82 ( ( x), ( x ')) = ( x) ˆ ( x ') 1 ˆ+ = Z+ exp( H+ ), Hˆ is a Hamiltonian of the field + ˆ in = / 2 is the inverse Hawking temperature (period of the Hawking-Gibbons instanton) R +,

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85 dm = TdS S = A 2 4 Pl

86 Entropy scales Stellar mass black hole (10 M ) S 10 Milky Way black hole ( M 410 M ) S Supermassive black hole ( M 10 M ) S All stars in the observable Universe S 10 Relic gravitons S 10 CMB photons S Relic neutrinos S A single Black Hole in the Milky Way has larger entropy than all visible matter in the observable Universe 79

87 What are microscopical degrees of freedom A responcible for BH e nt ropy S =? 2 4 l Pl

88 2 (1) Each (2 l Pl ) element of BH surface has 1 bit of entropy Quantum gravity is required (2) Universality problem: BH is determined by low energy physics parameters (3) BH is a ground (vacuum) state of classical gravitational field gravity should be an emergent phenomenon

89 A S, 2 BH = a = l 2 a a Pl N There exists =2 2-colored triangulations of the sphere for N-mono colored one. Entropy S S = ln = Nln 2 is:

90 If the quantum state of a pair of particles is in a definite superposition, and that superposition cannot be factored out into the product of two states (one for each particle), then that pair is entangled.

91 Quantum source of entropy for black holes, Bombelli, Koul, Lee, and Sorkin [Phys.Rev. D34, 373 (1986)] Entropy of a vacuum domain with a sharp A boundary S, A is the surface area l of the boundary. 2 cut off

92 Entropy and Area, by M. Srednicki, Phys. Rev. Lett. 71, 666 (1993). Dynamical origin of the entropy of a black hole by Frolov and Novikov, Phys.Rev. D48, 4545 (1993) Quantum fluctuations of the horizon as the origin of the ultraviolet cut-off.

93 ( ˆ ln ˆ ) S = Tr S + (volume contribution)+(surface contribution) (volume contribution) entropy of thermal radiation outside the black hole (surface contribution) entanglement entropy of Rindler particles near black hole horizon The latter is the black hole entropy: S A 2 Pl

94 Black Hole Potential barrier (') ˆ = Tr ˆ ; vacuum S = Tr( ˆ ln ˆ )

95 String theory AdF/CFT Loop gravity BH entropy problem Induced gravity 2+1 gravity Kerr/CFT

96 Collapse Evaporation Pure Black Thermal state hole radiation

97 If an initial pure state evolves into a mixed state, described by the density matrix, the unitarity of quantum evolution is lost. The unitarity is a basic principle of the quantum mechanics. Does it mean that Gravity + Quantum Mechanics= Inconsistent theory? Main ways out: 1. Quantum mechanics is still valid on a causal evolution of the initial Cauchy surface, but after evaporation an external observer has access only to a part of the system; 2. Information gradually leaks out during the evaporation process; 3. Information is collected in a small mass remnant; 4. Entanglement is immediately broken between the in-falling particle and the outgoing particle. A falling observer will see a `firewall, when he/she crosses the horizon.

98 5. No event horizon but only apparent horizon. Information returns `back after apparent horizon disappears. V.F. and G.Vilkovisky Spherically symmetric collapse in quantum gravity, Trieste preprint (1979), Phys.Lett. B106, 307 (1981) S.Hawking, January 22, 2014

99 Event horizon vs.apparent horizon

100 `Quasi-local definition of BH: Apparent horizon A compact smooth surface B is called a trapped surface if both, in- and out-going null surfaces, orthogonal to B, are non-expanding. A trapped region is a region inside B. A boundary of all trapped regions is called an apparent horizon. 100

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102 r plays the role of time inside BH Slice r = const has topology S 2 R Spatial volume r ( t / c) r 2 3 g g Contracting anisotropic universe

103 R 2 = R R = R M r M 6 r 2, M = r = 4 3 1/ M, cm, 7 10 cm

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105 Phenomenological description (i) There exists the critical energy scale parameter. The corresponding fundamental length is = ; c (ii) In the domain where with small corrections; (iii) In the domain where -2-2 the metric 2 obeys the Einstein equations the Einstein equations should be modified; C (iv) Limiting curvature condition:. C is a universal constant, defined by the theory and independent of the parameters of the solution. [Markov, JETP Lett. 36, 265 (1982)] Remark on inflation theory.

106 (i) An apparent horizon in a regular metric cannot cross r = 0. (ii) It has two branches: outer- and inner-horizons. (iii) Non-singular BH model with a closed apparent horizon [V.F. and G. Vilkovisky, Phys. Lett., 106B, 307 (1981)]

107 Non-singular model of black hole ds fdv dvdr r d = f 2Mr = 1, r 3 + 2M 2 2 Standard: =1; Modified: =. r r n + n n k n k + + n (2 M)

108 m * 1/6 = (27 / 4) M = 3 3 4

109 Non-singular model of an evaporating black hole ds = fdv + 2dvdr + r d 2 2 M( v) r f = 1 ( = 1) 3 2 r + 2 M( v) Mv () M 0 M 0 0 q v

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111 5 1+ r = 5, = 2.5, C = 1, = 1 (left) and = (right) r 0

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113 Evolution of the black hole concept: formal solutions of Einstein equations-> physical objects with amazing properties -> important elements of the Universe; The most powerful sources of energy; `Rosetta stones providing relations between different areas of physics;

114 Universal probes of new physics; An `arena for interesting applications of modern mathematics; Source of fundamental puzzles and problems; Philosophical problems; Role in the `very big picture of our Universe.