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Path: blob/master/sage/SageManifolds/SM_Simon-Mars_3p1_TS2.sagews
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3+1 Simon-Mars tensor in the Tomimatsu-Sato spacetime
This is a SageManifolds (version 0.7) worksheet implementing the computation of the 3+1 decomposition of the Simon-Mars tensor in the Tomimatsu-Sato spacetime. The results obtained here are used in the article arXiv:1412.6542.
The worksheet is released under the GNU General Public License version 2.
(c) Claire Somé, Eric Gourgoulhon (2015)
The worksheet file in Sage notebook format is here.
Tomimatsu-Sato spacetime
The Tomimatsu-Sato metric is an exact stationary and axisymmetric solution of the vacuum Einstein equation, which is asymptotically flat and has a non-zero angular momentum. It has been found in 1972 by A. Tomimatsu and H. Sato [Phys. Rev. Lett. 29, 1344 (1972)], as a solution of the Ernst equation. It is actually the member of a larger family of solutions parametrized by a positive integer and exhibited by Tomimatsu and Sato in 1973 [Prog. Theor. Phys. 50, 95 (1973)], the member being nothing but the Kerr metric. We refer to [Manko, Prog. Theor. Phys. 127, 1057 (2012)] for a discussion of the properties of this solution.
Spacelike hypersurface
We consider some hypersurface of a spacelike foliation of Tomimatsu-Sato spacetime; we declare as a 3-dimensional manifold:
On , we consider the prolate spheroidal coordinates , with , and :
Riemannian metric on
The Tomimatsu-Sato metric depens on three parameters: the integer , the real number , and the total mass :
We set and choose a specific value for , namely :
Furthermore, without any loss of generality, we may set (this simply fixes some length scale):
The parameter is related to by :
Some shortcut notations:
The Riemannian metric induced by the spacetime metric on :
A matrix view of the components w.r.t. coordinates :
Lapse function and shift vector
Extrinsic curvature of
We use the formula which is valid for any stationary spacetime:
The component :
The type-(1,1) tensor of components :
We may check that the hypersurface is maximal, i.e. that :
Connection and curvature
Let us call the Levi-Civita connection associated with :
The Ricci tensor associated with :
The scalar curvature :
Terms related to the extrinsic curvature
Let us first evaluate the term :
Then we compute the symmetric bilinear form :
We check that this tensor field is symmetric:
Accordingly, we work with the explicitly symmetric version:
Electric and magnetic parts of the Weyl tensor
The electric part is the bilinear form given by
The magnetic part is the bilinear form defined by
where are the components of the type-(1,2) tensor , related to the Levi-Civita alternating tensor associated with by . In SageManifolds, is obtained by the command volume_form() and by the command volume_form(1) (1 = 1 index raised):
Let us check that is symmetric:
Accordingly, we set
3+1 decomposition of the Simon-Mars tensor
We proceed according to the computation presented in arXiv:1412.6542.
Tensor of components :
Tensor of components :
1-form of components and its exterior derivative:
Scalar square of shift :
Scalar :
Scalar :
1-form of components :
Vector field of components :
1-form of components :
Vector field of components :
Vector field of components :
Simon-Mars scalars
Simon-Mars scalars expressed in terms of the coordinates :
Definition of the ergoregion:
Due to the very high degree of the polynomials involved in the expression of the Simon-Mars scalars, the floating-point precision of Sage's contour_plot function (53 bits) is not sufficient. Taking avantage that Sage is open-source, we modify the function to allow for an arbitrary precision. First, we define a sampling function with a floating-point precision specified by the user (argument precis):
Then we redefine contour_plot so that it uses the sampling function with a floating-point precision of 200 bits:
Then we are able to draw the contour plot of the two Simon-Mars scalars, in terms of the coordinates (Figure 11 of arXiv:1412.6542):
Let us do the same in terms of the Weyl-Lewis-Papapetrou cylindrical coordinates , which are related to the prolate spheroidal coordinates by
For simplicity, we denote by :
3D plots
Contour plots of the two Simon-Mars scalar fields in terms of coordinates (Figure 12 of arXiv:1412.6542)