246 research outputs found
The secular evolution of the Kuiper belt after a close stellar encounter
We show the effects of the perturbation caused by a passing by star on the
Kuiper belt objects (KBOs) of our Solar System. The dynamics of the Kuiper belt
(KB) is followed by direct -body simulations. The sampling of the KB has
been done with up to , setting the KBOs on initially nearly
circular orbits distributed in a ring of surface density .
This modelization allowed us to investigate the secular evolution of the KB
upon the encounter with the perturbing star. Actually, the encounter itself
usually leads toward eccentricity and inclination distributions similar to
observed ones, but tends also to excite the low-eccentricity population ( around \, from the Sun), depleting this region of
low eccentricities. The following long-term evolution shows a "cooling" of the
eccentricities repopulating the low-eccentricity area. In dependence on the
assumed KBO mass spectrum and sampled number of bodies, this repopulation takes
place in a time that goes from 0.5 Myr to 100 Myr. Due to the unavoidable
limitation in the number of objects in our long-term simulations (), we could not consider a detailed KBO mass spectrum, accounting for low
mass objects, thus our present simulations are not reliable in constraining
correlations among inclination distribution of the KBOs and other properties,
such as their size distribution. However, our high precision long term
simulations are a starting point for future larger studies on massively
parallel computational platforms which will provide a deeper investigation of
the secular evolution (Myr) of the KB over its whole mass spectrum.Comment: 13 pages, 12 figures, 5 table
Merging of globular clusters within inner galactic regions. II. The Nuclear Star Cluster formation
In this paper we present the results of two detailed N-body simulations of
the interaction of a sample of four massive globular clusters in the inner
region of a triaxial galaxy. A full merging of the clusters takes place,
leading to a slowly evolving cluster which is quite similar to observed Nuclear
Clusters. Actually, both the density and the velocity dispersion profiles match
qualitatively, and quantitatively after scaling, with observed features of many
nucleated galaxies. In the case of dense initial clusters, the merger remnant
shows a density profile more concentrated than that of the progenitors, with a
central density higher than the sum of the central progenitors central
densities. These findings support the idea that a massive Nuclear Cluster may
have formed in early phases of the mother galaxy evolution and lead to the
formation of a nucleus, which, in many galaxies, has indeed a luminosity
profile similar to that of an extended King model. A correlation with galactic
nuclear activity is suggested.Comment: 18 pages, 10 figures, 3 tables. Submitted to ApJ, main journa
Maximum Principle and generalized principal eigenvalue for degenerate elliptic operators
We characterize the validity of the Maximum Principle in bounded domains for fully nonlinear degenerate elliptic operators in terms of the sign of a suitably defined generalized principal eigenvalue. Here, the maximum principle refers to the property of non-positivity of viscosity subsolutions of the Dirichlet problem. The new notion of generalized principal eigenvalue that we introduce here allows us to deal with arbitrary type of degeneracy of the elliptic operators. We further discuss the relations between this notion and other natural generalizations of the classical notion of principal eigenvalue, some of which have been previously introduced for particular classes of operators
NBSymple, a double parallel, symplectic N-body code running on Graphic Processing Units
We present and discuss the characteristics and performances, both in term of
computational speed and precision, of a numerical code which numerically
integrates the equation of motions of N 'particles' interacting via Newtonian
gravitation and move in an external galactic smooth field. The force evaluation
on every particle is done by mean of direct summation of the contribution of
all the other system's particle, avoiding truncation error. The time
integration is done with second-order and sixth-order symplectic schemes. The
code, NBSymple, has been parallelized twice, by mean of the Computer Unified
Device Architecture to make the all-pair force evaluation as fast as possible
on high-performance Graphic Processing Units NVIDIA TESLA C 1060, while the
O(N) computations are distributed on various CPUs by mean of OpenMP Application
Program. The code works both in single precision floating point arithmetics or
in double precision. The use of single precision allows the use at best of the
GPU performances but, of course, limits the precision of simulation in some
critical situations. We find a good compromise in using a software
reconstruction of double precision for those variables that are most critical
for the overall precision of the code. The code is available on the web site
astrowww.phys.uniroma1.it/dolcetta/nbsymple.htmlComment: Paper composed by 29 pages, including 9 figures. Submitted to New
Astronomy
A fully parallel, high precision, N-body code running on hybrid computing platforms
We present a new implementation of the numerical integration of the
classical, gravitational, N-body problem based on a high order Hermite's
integration scheme with block time steps, with a direct evaluation of the
particle-particle forces. The main innovation of this code (called HiGPUs) is
its full parallelization, exploiting both OpenMP and MPI in the use of the
multicore Central Processing Units as well as either Compute Unified Device
Architecture (CUDA) or OpenCL for the hosted Graphic Processing Units. We
tested both performance and accuracy of the code using up to 256 GPUs in the
supercomputer IBM iDataPlex DX360M3 Linux Infiniband Cluster provided by the
italian supercomputing consortium CINECA, for values of N up to 8 millions. We
were able to follow the evolution of a system of 8 million bodies for few
crossing times, task previously unreached by direct summation codes. The code
is freely available to the scientific community.Comment: Paper submitted to Journal of Computational Physics consisting in 28
pages, 9 figures.The previous submitted version was lacking of the
bibliography, for a Tex proble
Self-consistent models of cuspy triaxial galaxies with dark matter haloes
We have constructed realistic, self-consistent models of triaxial elliptical
galaxies embedded in triaxial dark matter haloes. We examined three different
models for the shape of the dark matter halo: (i) the same axis ratios as the
luminous matter (0.7:0.86:1); (ii) a more prolate shape (0.5:0.66:1); (iii) a
more oblate shape (0.7:0.93:1). The models were obtained by means of the
standard orbital superposition technique introduced by Schwarzschild.
Self-consistent solutions were found in each of the three cases. Chaotic orbits
were found to be important in all of the models,and their presence was shown to
imply a possible slow evolution of the shapes of the haloes. Our results
demonstrate for the first time that triaxial dark matter haloes can co-exist
with triaxial galaxies.Comment: Latex paper based on the AASTEX format, 20 pages, 11 figures, 2
tables. Paper submitted to Ap
High performance astrophysics computing
The application of high end computing to astrophysical problems, mainly in
the galactic environment, is under development since many years at the Dep. of
Physics of Sapienza Univ. of Roma. The main scientific topic is the physics of
self gravitating systems, whose specific subtopics are: i) celestial mechanics
and interplanetary probe transfers in the solar system; ii) dynamics of
globular clusters and of globular cluster systems in their parent galaxies;
iii) nuclear clusters formation and evolution; iv) massive black hole formation
and evolution; v) young star cluster early evolution. In this poster we
describe the software and hardware computational resources available in our
group and how we are developing both software and hardware to reach the
scientific aims above itemized.Comment: 2 pages paper presented at the Conference "Advances in Computational
Astrophysics: methods, tools and outcomes", to be published in the ASP
Conference Series, 2012, vol. 453, R. Capuzzo-Dolcetta, M. Limongi and A.
Tornambe' ed
Elliptical galaxy nuclei activity powered by infalling globular clusters
Globular cluster systems evolve, in galaxies, due to internal and external
dynamics and tidal phenomena. One of the causes of evolution, dynamical
friction, is responsible for the orbital decay of massive clusters into the
innermost galactic regions. It is found that these clusters are effective
source of matter to feed a central galactic black hole such to make it grow and
shine as an AGN.Comment: 8 pages, 2 eps figures, in press in the Proc. of the Meeting Baryons
in Cosmic Structures, Monte Porzio (Italy), oct. 20-21 2003, ASP Conf. Ser.,
eds. E. Giallongo, G. De Zotti, N. Menc
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