Singularity formation in black hole interiors

Transcription

1 Singularity formation in black hole interiors Grigorios Fournodavlos DPMMS, University of Cambridge Heraklion, Crete, 16 May 2018

2 Outline The Einstein equations Examples Initial value problem Large time behaviour Global existence vs blow up Cosmic censorship hypothesis Spherical symmetry Resolution of the scalar field model Beyond spherical symmetry near Schwarzschild Construction of singular solutions Non-linear dynamics in polarized axisymmetry

3 1. The Einstein equations

4 The Einstein equations Geometric background: A Lorentzian manifold (M 1+3, g) of signature (, +, +, +), endowed with the topology M 1+3 = R Σ 3. g(x, X) > 0 g(l, L) = 0 g( γ, γ) < 0 γ L X Σ t γ

5 The Einstein equations The Einstein equations (EE) stipulate that g satisfies: R ab (g) 1 2 g abr(g) = 8πT ab, a, b = 0, 1, 2, 3, where R ab (g) is the Ricci curvature of g, R(g) its scalar curvature and T ab the energy-momentum tensor of a matter field (electromagnetic, fluid etc.), satisfying the conservation laws: 1 a T ab = 0, b = 0, 1, 2, 3. In vacuum, T ab = 0, the EE reduce to R ab (g) = 0, a, b = 0, 1, 2, 3. (EVE) 1 By virtue of the second Bianchi identity.

6 The Einstein equations Examples The flat solution: Minkowski (R 1+3, m), m = dt 2 + dx dx dx 2 3 t i + (t 0, p 1, p 2, p 3 ) r = 0 I + i 0 {(t t 0 ) 2 = 3 i=1 (x i p i ) 2 } i I

7 The Einstein equations Examples The Schwarzschild solution (M 1+3, g), M 1+3 = R R + S 2 : (vacuum & spherically symmetric) 2 g = (1 2M r )dt 2 + (1 2M r ) 1 dr 2 + r 2 ds 2, M > 0, i + r = 0 i + H ± = {r = 2M} BH := M 1+3 \ J (I + ) I + H + BH γ 1 H + γ 2 I + Riem r 3 i 0 I t = 0 H H I i 0 i r = 0 i 2 Rigidity, Birkhoff s theorem.

8 The Einstein equations Initial value problem In wave coordinates (x 0, x 1, x 2, x 3 ): g x i = 0, g = (g 1 ) ab ( ab Γ k ab k) Γ i := (g 1 ) ab Γ i ab = 0 the EVE take the hyperbolic form g g ab = Q(g 1, g) Theorem (Choquet-Bruhat & Geroch 69) Any asymptotically fact initial data set (Σ, g, K) for the EVE, gives rise to a unique maximal development.

9 The Einstein equations Initial data sets Minkowski: Σ = R 3, g = dx dx dx 2 3, K = 0. Schwarzschild: Σ = R S 2, g = (1 2M r ) 1 dr 2 + r 2 ds 2, K = 0. Constraint equations (in vacuum): { R(g) K 2 + (tr g K) 2 = 0 a K ab b tr g K = 0, b = 1, 2, 3

10 2. Large time behaviour

11 Large time behaviour Global existence vs Blow up The flat solution is stable: Christodoulou-Klainerman 93, Lindblad-Rodnianski 10,... The Schwarzschild exterior is linearly stable Dafermos-Holzegel-Rodnianski 16, within the Kerr family of solutions, K(a, M), a < M. CH + K(a, M), 0 < a < M CH + a = 0, Schwarzschild i + r = 0 i + I + H + H + I + i 0 i 0 Σ

12 Large time behaviour Global existence vs blow up No general blow up mechanism. Inside a black hole region, the space-time breaks down (Penrose 65). However, the nature of the breakdown is not given (geodesically incomplete). The presence of such a region is a stable phenomenon.

13 Large time behaviour Cosmic censorship hypothesis Theoretical tests of GR proposed by Penrose 69: Strong cosmic censorship hypothesis: Einsteinian maximal developments, for reasonable matter models, arising from generic, asymptotically flat initial data are inextendible as suitably regular Lorentzian manifolds. Weak cosmic censorship hypothesis: All future singularities should be contained in black holes (no naked singularities). In other words, future null infinity I + should be complete. Examples: The Minkowski and Schwarzschild solutions satisfy both weak and strong cosmic censorship, while Kerr satisfies weak cosmic censorship, but violates strong cosmic censorship.

14 3. Spherical symmetry

15 Spherical symmetry Resolution of the scalar field model Consider the energy-momentum tensor of a massless-scalar field: T ab = a ϕ b ϕ 1 2 g ab k ϕ k ϕ The Einstein equations are complemented with the equations of motion a T ab = 0: R ab (g) 1 2 g abr(g) = 8π( a ϕ b ϕ 1 2 g ab k ϕ k ϕ) g ϕ = 0

16 Spherical symmetry Resolution of the scalar field model Theorem (Christodoulou 90 s) Spherically symmetric solutions to the Einstein-scalar field equations, arising from asymptotically flat, 1-ended initial data fall in either of the three cases: I. Small data II. Large data i + r = 0 i + r = 0 I + r = 0 H + I + Σ i 0 Σ i0

17 Spherical symmetry Resolution of the scalar field model and III. Naked singularity r = 0 I + However, the third case is unstable (non-generic). Σ

18 4. Beyond spherical symmetry near -Schwarzschild

19 Beyond spherical symmetry near Schwarzschild Exterior region: Conjecturally stable, within the Kerr family of solutions. Only linearised stability has been proven. Interior region: Conjectural picture is unknown. Singularity formation or violation of strong cosmic censorship (as in Kerr)? Spacelike or null inner boundary? Monotonic blow up or chaotic? (BKL)

20 Beyond spherical symmetry near Schwarzschild Construction of singular solutions Idea: Prescribe initial data for the EVE at Σ 0, such that g = g S + r α h, K = K S + r α u, h, u smooth, α > 0, and solve backwards-in-time, without any symmetry assumptions. r = 0 Σ 0 Σ 1 Theorem (F. 16) For α 1, such a construction is possible, generating solutions to the EVE which exhibit a Schwarzschild type singularity at a collapsed sphere.

21 Beyond spherical symmetry near Schwarzschild Non-linear dynamics in polarized axisymmetry Assume g admits a spacelike Killing vector field ϕ with S 1 orbits, which is also hypersurface orthogonal: g = h ab dx a dx b + e 2γ dϕ 2 a,b=0,1,2 In this symmetry class, the EVE reduce to the system (Weinstein 90): g γ = 0 R ab (h) = ab γ + a γ b γ Note: Under the additional conformal change h := e 2γ h, the above equations transform into the Einstein-scalar field model.

22 Beyond spherical symmetry near Schwarzschild Non-linear dynamics in polarized axisymmetry The Schwarzschild solution: h S = ( 2M r 1) 1 dr 2 + ( 2M r 1)dt 2 + r 2 dθ 2, γ S = log r + log sin θ On the other hand, the Kerr metric is axisymmetric, but not polarized. Restricting to polarized axisymmetric perturbations of Schwarzschild: Exterior region: Conjectural asymptotic convergence to Schwarzschild (possibly of different M), see Klainerman-Szeftel 17. Interior region: (work on progress w/ Alexakis) Strong evidence for stable spacelike singularity formation, where Riem r 3.