| Full text | |
| Author(s): |
Beraldo e Silva, Leandro
[1, 2]
;
Pedra, Walter de Siqueira
[3]
;
Valluri, Monica
[1]
;
Sodre, Laerte
[2]
;
Bru, Jean-Bernard
[4, 5, 6]
Total Authors: 5
|
| Affiliation: | [1] Univ Michigan, Dept Astron, Ann Arbor, MI 48109 - USA
[2] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Dept Astron, BR-05508090 Sao Paulo, SP - Brazil
[3] Univ Sao Paulo, Inst Fis, Dept Fis Matemat, CP 66318, BR-05314970 Sao Paulo, SP - Brazil
[4] Univ Basque Country, Fac Ciencia & Tecnol, Dept Matemat, Apartado 644, E-48080 Bilbao - Spain
[5] BCAM, Mazarredo 14, E-48009 Bilbao - Spain
[6] Basque Fdn Sci, IKERBASQUE, E-48011 Bilbao - Spain
Total Affiliations: 6
|
| Document type: | Journal article |
| Source: | ASTROPHYSICAL JOURNAL; v. 870, n. 2 JAN 10 2019. |
| Web of Science Citations: | 0 |
| Abstract | |
We investigate the old problem of the fast relaxation of collisionless N-body systems that are collapsing or perturbed, emphasizing the importance of (noncollisional) discreteness effects. We integrate orbit ensembles in fixed potentials, estimating the entropy to analyze the time evolution of the distribution function. These estimates capture the correct physical behavior expected from the second law of thermodynamics, without any spurious entropy production. For self-consistent (i.e., stationary) samples, the entropy is conserved, while for non-self-consistent samples, it increases within a few dynamical times, stabilizing at a maximum (even in integrable potentials). Our results make transparent that the main ingredient for this fast collisionless relaxation is the discreteness (finite N) of gravitational systems in any potential. Additionally, in nonintegrable potentials, the presence of chaotic orbits accelerates the entropy production. Contrary to the traditional violent relaxation scenario, our results indicate that a time-dependent potential is not necessary for this relaxation. For the first time, in connection with the Nyquist-Shannon theorem, we derive the typical timescale T / tau(cr) approximate to 0.1N(1/6) for this discreteness-driven relaxation, with slightly weaker N-dependencies for nonintegrable potentials with substantial fractions of chaotic orbits. This timescale is much smaller than the collisional relaxation time even for small-N systems such as open clusters and represents an upper limit for the relaxation time of real N-body collisionless systems. Additionally, our results reinforce the conclusion of Beraldo e Silva et al. that the Vlasov equation does not provide an adequate kinetic description of the fast relaxation of collapsing collisionless N-body systems. (AU) | |
| FAPESP's process: | 14/23751-4 - Dynamics and Statistical Mechanics of dark matter halos |
| Grantee: | Leandro José Beraldo e Silva |
| Support Opportunities: | Scholarships in Brazil - Post-Doctoral |
| FAPESP's process: | 09/54006-4 - A computer cluster for the Astronomy Department of the University of São Paulo Institute of Astronomy, Geophysics and Atmospheric Sciences and for the Cruzeiro do Sul University Astrophysics Center |
| Grantee: | Elisabete Maria de Gouveia Dal Pino |
| Support Opportunities: | Multi-user Equipment Program |
| FAPESP's process: | 17/22340-9 - Constructive methods for interacting fermions with applications to the microscopic theory of conductivity and superconductivity |
| Grantee: | Walter Alberto de Siqueira Pedra |
| Support Opportunities: | Research Grants - Visiting Researcher Grant - International |