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(Referência obtida automaticamente do Web of Science, por meio da informação sobre o financiamento pela FAPESP e o número do processo correspondente, incluída na publicação pelos autores.)

The Arrow of Time in the Collapse of Collisionless Self-gravitating Systems: Non-validity of the Vlasov-Poisson Equation during Violent Relaxation

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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: 14/23751-4 - Dinâmica e mecânica estatística de halos de matéria escura
Beneficiário:Leandro José Beraldo e Silva
Linha de fomento: Bolsas no Brasil - Pós-Doutorado
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
Linha de fomento: Auxílio à Pesquisa - Programa Equipamentos Multiusuários
Processo FAPESP: 16/02503-8 - Comportamento macroscópico de sistemas de férmions não relativísticos interagentes
Beneficiário:Walter Alberto de Siqueira Pedra
Linha de fomento: Bolsas no Exterior - Pesquisa
Processo FAPESP: 12/00800-4 - O universo em 3-D: astrofísica com grandes levantamentos de galáxias
Beneficiário:Laerte Sodré Junior
Linha de fomento: Auxílio à Pesquisa - Temático
Processo FAPESP: 12/16835-1 - A aceleração cósmica e o Dark Energy Survey
Beneficiário:Marcos Vinicius Borges Teixeira Lima
Linha de fomento: Auxílio à Pesquisa - Regular