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Black Hole Universe
Yoo, Chulmoon ( YITP)
Hiroyuki Abe (Osaka City Univ.)Ken-ichi Nakao (Osaka City Univ.) Yohsuke Takamori (Osaka City Univ.)
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Chulmoon Yoo
2Cluster of Many BHs ~ Dust Fluids?
Naively thinking, we can treat the cluster of a number of BHs as a dust fluid on average
In this work, as a simplest case, we try to construct “the BH universe” which would be approximated by the EdS universe on average
But, it is very difficult to show it from the first principle. Because we need to solve the N-body dynamics with the Einstein equations.
dust fluid~~
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Lattice Universe“Dynamics of a Lattice Universe by the Schwarzschild-Cell Method” [Lindquist and Wheeler(1957)]
The maximum radius asymptotically agrees with the dust universe case
Putting N equal mass Sch. BHs on a 3-sphere, requiring a matching condition, we get a dynamics of the lattice universe
maximum radius of lattice universe
number of BHs
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Swiss-cheese Universe
Expand
Homogeneous dust universe
Cutting spherical regions, put Schwarzschild BHs with the same mass
Swiss-cheese universe
We want to make it without cheese(“Swiss universe” ?)
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Some Aspects of This Work
If perturbations of metric components are small enough, we don’t need to treat full GR but perturbation theory is applicable. Perhaps, even if the density perturbation is nonlinear in small scales, we could handle the inhomogeneities without full numerical relativity.
1. “Cosmological Numerical Relativity (CNR)”In which situation, CNR may be significant?
(In this sense, for late time cosmology, CNR might not be significant.)
CNR may play a role in an extreme situation where the metric perturbation is full nonlinear on cosmological scales (e.g. primordial BH formation)
2. BH simulation without asymptotic flatness-In higher-dimensional theory, compactified directions often exist, and they are not asymptotically flat. -BH physics might be applied to other fields (e.g. AdS/CFT,QCD,CMP) without asymptotic flatness
Their dynamical simulations might have common feature?
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Contents
◎Part 1 : “A recipe for the BH universe”How to construct the initial data for the BH universe
◎Part 2 “ Structure of the BH universe”- Horizons- Effective Hubble equation with an averaging
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Part 1A recipe for the BH
universe
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…
What We Want to Do
◎Vacuum solution for the Einstein eqs.
First, we construct the puncture initial data
◎Expansion of the universe is crucial to avoid the potential divergence
Periodic boundary
ExpandingBH
…
…
…
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PunctureBoundary
Infinity of the other world
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Constraint Eqs.
We assume
Setting trK by hand, we solve these eqs.How should we choose trK?
We construct the initial data.
where
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Chulmoon Yoo
11Expansion of the universe
tr K must be a finite value around the boundary
Expand
finite Hubble parameter HH =-tr K / 3
→Swiss-cheese case
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CMC (constant mean curvature) Slicetr K = const. ⇔ ∇ana=const.
induced metric
isotropic coordinate
CMC slice
?
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r=∞ r=∞
R=Rc
For K≠0, we have a finite R at r=∞
We need to take care of the inner boundary
To avoid this, we choose K=0 near the infinity(maximal slice)
r=∞
R=0
Difficulty to use CMC slice
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trK
CMC sliceMaximal slice
trK
/Kc
R
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Constraint Eqs.
Extraction of 1/R divergence
Near the center R=0 (trK=0)
ψ is regular at R=0
Periodic boundary condition for ψ and Xi
1
* f=0 at the boundary
r=∞
R=0
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Equations
xy
z
L
R:=(x2+y2+z2)1/2
Source terms must vanish by integrating in a box
Poisson equation with periodic boundary condition
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Integration of source terms
vanishes by integrating in the box because ∂x Z and ∂x K are odd function of x
Vanishes by integrating in the box because K=const. at the boundary
Integration of this part also must vanish
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18Effective Hubble Equation
Integrating in a box, we have
Hubble parameter H
effective mass density
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Parameters•BH mass•Box size (isotropic coord.)
•Hubble radius
We set Kc so that the following equation is satisfied
This is just the integration of the constraint equation. We update the value of Kc at each step of the numerical iteration.
Free parameter is only
other than and
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Part 2Structure of the BH
universe
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Parameter Settings
L/M 2 3 4 5
σ/M 1.3 2 2.7 3.4
l/M=0.6 (horizon is at R~ 0.5)
trK
/Kc
R
0.6
hori
zon
σ
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Numerical Solutions(1)
xy
z
L
ψ(x,y,L) for L=2M
ψ(x,y,0) for L=2M
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Numerical Solutions(2)Z(x,y,L) for L=2M
Z(x,y,0) for L=2M
xy
z
L
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Numerical Solutions(3)
Xx(x,y,L) for L=2M
Xx(x,y,0) for L=2M
xy
z
L
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Convergence Test
◎2nd order convergence has been checked for some cases
◎We are now checking the other cases...
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Horizons ◎To see Horizons, we calculate outgoing(+) and ingoing(-) null expansions of spheres
◎We plot the value of χ for three independent directions (χ is not spherically symmetric in general)
: unit normal vector to sphere
◎Horizons (approximate position): Black hole horizon
: White hole horizon
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Expansion ◎parameter : L=2M
χ+
χ-
◎Horizons are almost spherically symmetric
◎BH and WH horizons are almost identical in our settings, i.e., bifurcation point
R
exp
an
sio
n
horizon
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Time slice◎BH horizon always exists outside WH horizon
BH horizon
“WH horizon”Bifurcation point
We would have this case changing the trK profile but it’s relatively numerically unstable and hasn’t passed the convergence test
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Inhomogeneity
(x,y,L) for L=2M
(x,y,0) for L=2M
xy
z
L
◎Square of the traceless part of 3-dim Ricci curvature
homogeneous ⇔
homogeneous and empty⇒Milne universe (ΩK=1)
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Inhomogeneity(x,y,L) for L=2M
(x,y,L) for L=4M(x,y,L) for L=5M0.6
0.6
0.7
Not homogeneous around the center of a boundary face
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Effect of Xi
(x,y,L) for L=2M
(x,y,L) for L=4M(x,y,L) for L=5M0.08
0.05
0.4
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An Averaging◎Effective density
xy
z
L
Area:
Effective volume of a box ( )
Effective density
◎Hubble parameter (defined by the boundary value of trK)
◎We may expect (?)
This relation is nontrivial!
No dust, No matter, No symmetry, but additional gravitational energy other than “the point mass”
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Effective Hubble◎Effective Hubble parameter
◎It asymptotically agrees with the expected value!
H2M
2
S/M2
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Conclusion◎We constructed initial data for the BH universe
◎What about the evolution...? future work...?
◎BH and WH horizon are are almost identical in our settings, i.e., bifurcation point
◎If the box size is much larger than the Schwarzschild radius of the mass M, an effective density and an effective Hubble parameter satisfy Hubble equation of the EdS universe, that is, the BH universe is the EdS universe on Average!
◎Around vertices, it is Milne universe
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Thank you very much!