Universal non-Gaussian velocity distribution in violent gravitational processes

Iguchi, Osamu; Sota, Yasuhide; Tatekawa, Takayuki; Nakamichi, Akika; Morikawa, Masahiro

doi:10.1103/physreve.71.016102

Cited by 25 publications

(37 citation statements)

References 13 publications

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“…For velocity distributions in the sphere, we examine onedimensional velocity distribution functions combining alldirectional components of the velocity distribution [32]. The velocity distribution function f (v) is first averaged over 30 simulations.…”

Section: Parameters For Simulationsmentioning

confidence: 99%

“…In these systems, the velocity distributions are non-Gaussian [31][32][33], especially in quasiequilibrium states and metastable states. For example, Iguchi et al proposed universal non-Gaussian velocity distributions for a spherical collapse in a violent gravitational process of a collisionless stage (t < τ r ) [32], and Carvalho et al indicated that the q parameter in the Tsallis distribution depends on the age of open stellar clusters [33]. (Here τ r represents the relaxation time, which is driven by the two-body encounter [1]).…”

Section: Introductionmentioning

confidence: 99%

“…However, velocity distributions have not yet been extensively discussed in long-term nonequilibrium processes, * komatsu@t.kanazawa-u.ac.jp except for a few studies [1,[32][33][34][35], although they should play an important role in the thermodynamic properties of a system. In other words, it is not yet understood completely how the velocity distribution evolves from an early relaxation to a collapse.…”

Section: Introductionmentioning

confidence: 99%

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Transition of velocity distributions in collapsing self-gravitatingN-body systems

Komatsu

Kiwata

2012

Phys. Rev. E

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By means of N -body simulations, we study the evolution of gravity-dominated systems from an early relaxation to a collapse, focusing on the velocity distributions and thermodynamic properties. To simulate the dynamical evolution, we consider self-gravitating small N -body systems enclosed in a spherical container with adiabatic or semipermeable walls. It is demonstrated that in the early relaxation process, the velocity distribution is non-Gaussian and q-Gaussian, since the system is in quasiequilibrium states (here q is the Tsallis entropic parameter). Thereafter, the velocity distribution undergoes higher non-Gaussian distributions, especially when the core forms rapidly in the collapse process; i.e., q tends to be larger than that for the quasiequilibrium state, since the velocity distribution further deviates from Gaussian. However, after the core forms sufficiently, the velocity distribution gradually relaxes toward a Gaussian-like distribution. Accordingly, the velocity distribution evolves from a non-Gaussian distribution through a higher non-Gaussian distribution to a Gaussian-like distribution; i.e., the velocity distribution does not monotonically relax toward a Gaussian-like distribution in our collapse simulations. We clearly show such a transition of the velocity distribution, based not only on the Tsallis entropic parameter but also on the ratio of velocity moments. We also find that a negative specific heat occurs in a collapse process with mass and energy loss (such as the escape of stars from globular clusters), even if the velocity distribution is Gaussian-like.

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Section: Parameters For Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Transition of velocity distributions in collapsing self-gravitatingN-body systems

Komatsu

Kiwata

2012

Phys. Rev. E

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“…Numerical simulations of collapse and relaxation processes of self-gravitating collisionless systems, similar to galaxies, are useful in identifying their general trends, such as density and anisotropy profiles. Two studies of the velocity distribution function of these systems by means of numerical simulations were performed, showing that the velocity distribution of the resultant quasi-stationary states generally becomes non-Gaussian (Iguchi et al 2005;Hansen et al 2006). …”

Section: Non-gaussian Velocity Distributionsmentioning

confidence: 99%

Microlensing towards the LMC revisited by adopting a non-Gaussian velocity distribution for the sources

Mancini

2009

A&A

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Aims. We discuss whether the Gaussian is a reasonable approximation of the velocity distribution of stellar systems that are not spherically distributed. Methods. By using a non-Gaussian velocity distribution to describe the sources in the Large Magellanic Cloud (LMC), we reinvestigate the expected microlensing parameters of a lens population isotropically distributed either in the Milky Way halo or in the LMC (self lensing). We compare our estimates with the experimental results of the MACHO collaboration.Results. An interesting result that emerges from our analysis is that, moving from the Gaussian to the non-Gaussian case, we do not observe any change in the form of the distribution curves describing the rate of microlensing events for lenses in the Galactic halo. The corresponding expected timescales and number of expected events also do not vary. Conversely, with respect to the self-lensing case, we observe a moderate increase in the rate and number of expected events. We conclude that the error in the estimate of the most likely value for the MACHO mass and the Galactic halo fraction in form of MACHOs, calculated with a Gaussian velocity distribution for the LMC sources, is not higher than 2%.

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“…We discuss the equilibrium properties of the Self Gravitating Ring (SGR) model, a toy model for self gravitating systems. Whereas we mainly present here its equilibrium properties, we stress that this system is very interesting also from a dynamical point of view, as it shows a number of out of equilibrium quasi-stationary states [31,32].…”

Section: Figurementioning

confidence: 99%

Equilibrium and out of equilibrium phase transitions in systems with long range interactions and in 2D flows

Bouchet¹,

Barré²,

Venaille

2008

AIP Conference Proceedings

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Abstract. In self-gravitating stars, two dimensional or geophysical flows and in plasmas, long range interactions imply a lack of additivity for the energy; as a consequence, the usual thermodynamic limit is not appropriate. However, by contrast with many claims, the equilibrium statistical mechanics of such systems is a well understood subject. In this proceeding, we explain briefly the classical approach to equilibrium and non equilibrium statistical mechanics for these systems, starting from first principles. We emphasize recent and new results, mainly a classification of equilibrium phase transitions, new unobserved equilibrium phase transition, and out of equilibrium phase transitions.We briefly discuss what we consider as challenges in this field.

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Universal non-Gaussian velocity distribution in violent gravitational processes

Cited by 25 publications

References 13 publications

Transition of velocity distributions in collapsing self-gravitatingN-body systems

Transition of velocity distributions in collapsing self-gravitatingN-body systems

Microlensing towards the LMC revisited by adopting a non-Gaussian velocity distribution for the sources

Equilibrium and out of equilibrium phase transitions in systems with long range interactions and in 2D flows

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