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VALENCIA
(A) The Valencia Team and Organizational Developments
The group of relativistic astrophysics in Valencia has been in operation since
the end of 1980s. Current members of the group are:
José M
(B) Scientific Highlights
I. Numerical Relativistic Hydro(-Magneto)dynamics
The exact solution of the Riemann problem (RP) with non-zero tangential velocities in relativistic hydrodynamics has been obtained by Pons, Martí & Müller (see [7], [15]) by solving the jump conditions across the shocks plus an ordinary differential equation arising from the self-similarity condition along rarefaction waves. The knowledge of the exact solution of the RP allows one to derive an exact Riemann solver in the field of (multidimensional) relativistic hydrodynamics. This paper is a keystone in the way of generating multidimensional tests to be overcome by any multidimensional relativistic hydro-code (based on Riemann solvers or not). In [6] we have explored the possibility of extending modern high-resolution shock-capturing (HRSC) techniques to the field of radiative transfer. A very interesting by-product of this analysis is the existence of constraints on the closure relation coming from the assumption of hyperbolicity. We have started to build up a multidimensional relativistic magnetohydrodynamic (RMHD) code, based on HRSC techniques. Some preliminar results with a Newtonian version can be found in [9]. Currently, we have already developed a RMHD code for the particular case in which the magnetic field is assumed to be passive.
II. Hydrodynamical Simulations of Astrophysical Sources of Gravitational Radiation
In [8] we have analyzed the features of the gravitational radiation coming from a given spatial distribution of galaxy clusters. The simulations of the formation of an isolated galaxy cluster were made (in previous papers) using a 3D Eulerian code (for the baryonic component), which incorporates modern HRSC techniques, coupled -through Poisson's equation- to a N-body code (for the dark matter component).
With Dr. Novak (member of the Meudon node) we have studied [5] the collapse of a degenerate stellar core, within tensor-scalar theory of gravity, leading to the formation of a neutron star through a bounce and the formation of a shock. As a main result, we describe the resulting gravitational monopolar radiation (form and amplitude) and discuss the possibilitiy of its detection by the gravitational detectors currently under construction. As a by-product of this work, we have succeeded in building a hybrid code which couples the state-of-the-art of modern HRSC techniques and pseudo-spectral methods.
III. Simulations of relativistic flows
We continue working in our line of research concerning the study of relativistic flows in astrophysical systems such as: extragalactic relativistic jets, relativistic jets from collapsars and accreting relativistic flows onto a black hole. Although the two first topics are not directly related with the objectives of the network I consider that they might be of interest for some members of the network, at least from the point of view of the application of numerical techniques, in relativistic hydrodynamics (HRSC), which are also used, in their general-relativistic extension, by researchers in some of the nodes of the network.
III.1 Extragalactic relativistic jets
The first radio emission simulations from high-resolution three-dimensional relativistic jets have been presented in [1] and [10]. They have been generated running GENESIS, an optimized and parallelized 3D special relativistic hydro-code, which is suited for massively parallel computers with distributed memory. A general-relativistic version of GENESIS is currently in progress.
III.2 Relativistic Jets from Collapsars
In [2], [14] and [11] we have analyzed, in the
framework of the theory of
special relativity, the formation of Gamma-Ray Bursts according to the
previous suggestions, in the Newtonian case, of MacFadyen & Woosley.
Using a collapsar progenitor provided by MacFadyen & Woosley, we have
simulated the propagation of an axisymmetric jet through a collapsing
rotating massive star with GENESIS. The jet forms as a consequence of
an assumed energy deposition in the range
III.3 Accretion onto a Black Hole
We have developed a numerical code to study the evolution of self- gravitating matter in dynamic black hole axisymmetric spacetimes in general relativity. In [3] we make some studies of the spherical and axisymmetric accretion onto a dynamic black hole, the fully dynamical evolution of imploding shells of dust with a black hole, the evolution of matter in rotating spacetimes, the gravitational radiation induced by the presence of the matter fields and the behavior of apparent horizons through the evolution.
IV. Physics of Compact Objects
In a collaboration with professor Vadim Urpin (IOFFE Institute, Saint Petersburg, now on sabbatical at the University of Valencia) The different criteria of convective instability have been exhaustively analyzed [4] in the scenario of new-born neutron stars.
In his Ph.D. Thesis, developed in Valencia under the supervision of J.A. Miralles, J.A. Pons built up a general relativistic stellar evolutionary code. Particular attention was payed on the neutrino transport in the interior of a proto-neutron star. With this code was possible to carry out detailed calculations of the cooling of a proto-neutron star and their neutrino spectra, for different equations of state ([13], [16] and [17]).
(C) Visits and Collaboration
Next: References Up: Introduction Previous: Development of perturbation equations for
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. Ibáñez (Prof.,
Local Coordinator), Juan A. Miralles (Assoc. Prof., since October 2000 in
the University of Alicante),
Armando Pérez (Assoc. Prof.),
José M 
ergs s 
within a 
cone around the rotation axis. The jet flow is strongly
beamed, spatially inhomogeneous, and time dependent. Outside the star, the flow
begins to expand laterally but the beam remains very well collimated.
When the simulation ends, the Lorentz factor has increased up to 44.