Violent relaxation of ellipsoidal clouds

Benhaiem, David; Labini, Francesco Sylos

doi:10.1093/mnras/stv075

Cited by 15 publications

(24 citation statements)

References 23 publications

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“…We remark finally that a very similar dynamical process was observed by Benhaiem & Sylos Labini (2015) for the case of initial conditions given by uniform ellipsoids. In addition, we note that Theis & Spurzem (1999) considered a Plummer density profile with a very small initial virial ratio, finding that a fast dynamical collapse generates at its end the maximal triaxiality of the system: the dynamical mechanism that generates such a triaxial structure is the same at work in the power-law density profile.…”

Section: Symmetry Breaking Of Relaxed Statesupporting

confidence: 80%

“…The cases in which α is outside this range are numerically more challenging because of singularities -discussed further below -both for α = 0 and α = 3 in the limit N → ∞. For these cases we have subjected our results to additional tests of their robustness, checking their stability in particular to smaller time-steps (see also the discussion in Joyce, Marcos & Sylos Labini (2009);Benhaiem & Sylos Labini (2015)). We have also studied carefully the effects of varying the force smoothing parameter (corresponding to its small scale at small distances), and we have found our results to be stable provided it is significantly smaller than the minimal characteristic size (see below) attained by the structure during its collapse For the simulations reported below the smoothing parameter is always in this latter range.…”

Section: Numerical Simulationsmentioning

confidence: 99%

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On the generation of triaxiality in the collapse of cold spherical self-gravitating systems

Labini¹,

Benhaiem²,

Joyce

2015

Monthly Notices of the Royal Astronomical Society

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Initially cold and spherically symmetric self-gravitating systems may give rise to a virial equilibrium state which is far from spherically symmetric, and typically triaxial. We focus here on how the degree of symmetry breaking in the final state depends on the initial density profile. We note that the most asymmetric structures result when, during the collapse phase, there is a strong injection of energy preferentially into the particles which are localized initially in the outer shells. These particles are still collapsing when the others, initially located in the inner part, are already reexpanding; the motion of particles in a time varying potential allow them to gain kinetic energy -in some cases enough to be ejected from the system. We show that this mechanism of energy gain amplifies the initial small deviations from perfect spherical symmetry due to finite N fluctuations. This amplification is more efficient when the initial density profile depends on radius, because particles have a greater spread of fall times compared to a uniform density profile, for which very close to symmetric final states are obtained. These effects lead to a distinctive correlation of the orientation of the final structure with the distribution of ejected mass, and also with the initial (very small) angular fluctuations.

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Section: Symmetry Breaking Of Relaxed Statesupporting

confidence: 80%

Section: Numerical Simulationsmentioning

confidence: 99%

On the generation of triaxiality in the collapse of cold spherical self-gravitating systems

Labini¹,

Benhaiem²,

Joyce

2015

Monthly Notices of the Royal Astronomical Society

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“…As mentioned above, the collapse of an ellipsoidal cloud is characterized by a mechanism of energy gain that amplifies the initial small deviations from spherical symmetry (Benhaiem & Sylos Labini 2015). This interpretation is supported by the fact that the largest semi-axis (i.e.…”

Section: Weakly Bounded Particlesmentioning

confidence: 73%

Formation of satellites from cold collapse

Benhaiem

Labini

2017

A&A

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Abstract. We study the collapse of an isolated, initially cold, irregular (but almost spherical) and (slightly) inhomogeneous cloud of self-gravitating particles.The cloud is driven towards a virialized quasi-equilibrium state by a fast relaxation mechanism, occurring in a typical time τc, whose signature is a large change in the particle energy distribution. Post-collapse particles are divided into two main species: bound and free, the latter being ejected from the system. Because of the initial system's anisotropy, the time varying gravitational field breaks spherical symmetry so that the ejected mass can carry away angular momentum and the bound system can gain a non-zero angular momentum. In addition, while strongly bound particles form a compact core, weakly bound ones may form, in a time scale of the order of τc, several satellite sub-structures. These satellites have a finite lifetime that can be longer than τc and generally form a flattened distribution. Their origin and their abundance are related to the amplitude and nature of initial density fluctuations and to the initial cloud deviations from spherical symmetry, which are both amplified during the collapse phase. Satellites show a time dependent virial ratio that can be different from the equilibrium value b ≈ −1: although they are bound to the main virialized object, they are not necessarily virially relaxed.

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“…To explain the emergence of the two controlled arms, let us recall the related work of Benhaiem & Sylos Labini (2015). During the collapse of a nonrotating ellipsoid, they demonstrate that the inertial principal axis of ejection is strongly aligned with the initial major axis of the system.…”

Section: Numerical Resultsmentioning

confidence: 99%

Formation of spiral structure from the violent relaxation of self‐gravitating disks

Worrakitpoonpon

2020

Astron Nachr

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We present the numerical study of the formation of a spiral structure in the context of violent relaxation. Initial conditions are the out‐of‐equilibrium disks of self‐gravitating particles in rigid rotation. Using that mechanism, robust and nonstationary spiral arms can be formed within a few free‐fall times through the shearing of mass ejection following the collapse. With a closer look, we find different properties of the arms in connection with the initial configuration. The winding degree tends to increase with initial angular speed provided that a disk is thin. If the disk surface is circular, both the number and position of arms are governed by the Poissonian density fluctuations that produce more arms as more particles are introduced. On the contrary, if the surface ellipticity is imposed, the number of arms and their placement are effectively controlled. Otherwise, the increase in thickness leads to a complicated outcome as the number of arms and winding degree are less effectively controlled. We speculate that this complexity is caused by a strong nonaxisymmetric field during the violent relaxation that disorganizes the precollapse motion and the concentration of particles.

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Violent relaxation of ellipsoidal clouds

Cited by 15 publications

References 23 publications

On the generation of triaxiality in the collapse of cold spherical self-gravitating systems

On the generation of triaxiality in the collapse of cold spherical self-gravitating systems

Formation of satellites from cold collapse

Formation of spiral structure from the violent relaxation of self‐gravitating disks

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