| Texto completo | |
| Autor(es): |
Beraldo e Silva, Leandro
;
Pedra, Walter de Siqueira
;
Sodre, Laerte
;
Perico, Eder L. D.
;
Lima, Marcos
Número total de Autores: 5
|
| Tipo de documento: | Artigo Científico |
| Fonte: | ASTROPHYSICAL JOURNAL; v. 846, n. 2 SEP 10 2017. |
| Citações Web of Science: | 1 |
| Resumo | |
The collapse of a collisionless self-gravitating system, with the fast achievement of a quasi-stationary state, is driven by violent relaxation, with a typical particle interacting with the time-changing collective potential. It is traditionally assumed that this evolution is governed by the Vlasov-Poisson equation, in which case entropy must be conserved. We run N-body simulations of isolated self-gravitating systems, using three simulation codes, NBODY-6 (direct summation without softening), NBODY-2 (direct summation with softening), and GADGET-2 (tree code with softening), for different numbers of particles and initial conditions. At each snapshot, we estimate the Shannon entropy of the distribution function with three different techniques: Kernel, Nearest Neighbor, and EnBiD. For all simulation codes and estimators, the entropy evolution converges to the same limit as N increases. During violent relaxation, the entropy has a fast increase followed by damping oscillations, indicating that violent relaxation must be described by a kinetic equation other than the Vlasov-Poisson equation, even for N as large as that of astronomical structures. This indicates that violent relaxation cannot be described by a time-reversible equation, shedding some light on the so-called ``fundamental paradox of stellar dynamics.{''} The long-term evolution is well-described by the orbit-averaged Fokker-Planck model, with Coulomb logarithm values in the expected range 10-12. By means of NBODY-2, we also study the dependence of the two-body relaxation timescale on the softening length. The approach presented in the current work can potentially provide a general method for testing any kinetic equation intended to describe the macroscopic evolution of N-body systems. (AU) | |
| Processo FAPESP: | 12/00800-4 - O universo em 3-D: astrofísica com grandes levantamentos de galáxias |
| Beneficiário: | Laerte Sodré Junior |
| Modalidade de apoio: | Auxílio à Pesquisa - Temático |
| Processo FAPESP: | 09/54006-4 - Um cluster de computadores para o Departamento de Astronomia do IAG-USP e para o Núcleo de Astrofísica da UNICSUL |
| Beneficiário: | Elisabete Maria de Gouveia Dal Pino |
| Modalidade de apoio: | Auxílio à Pesquisa - Programa Equipamentos Multiusuários |
| Processo FAPESP: | 12/16835-1 - A aceleração cósmica e o Dark Energy Survey |
| Beneficiário: | Marcos Vinicius Borges Teixeira Lima |
| Modalidade de apoio: | Auxílio à Pesquisa - Regular |
| Processo FAPESP: | 14/23751-4 - Dinâmica e Mecânica Estatística de Halos de Matéria Escura |
| Beneficiário: | Leandro José Beraldo e Silva |
| Modalidade de apoio: | Bolsas no Brasil - Pós-Doutorado |
| Processo FAPESP: | 16/02503-8 - Comportamento macroscópico de sistemas de férmions não relativísticos interagentes |
| Beneficiário: | Walter Alberto de Siqueira Pedra |
| Modalidade de apoio: | Bolsas no Exterior - Pesquisa |