scholarly journals Simulation of the loss-cone instability in spherical systems – II. Dominating Keplerian potential

2020 ◽  
Vol 492 (4) ◽  
pp. 4819-4824
Author(s):  
E V Polyachenko ◽  
P Berczik ◽  
A Just ◽  
I G Shukhman
Keyword(s):  
Phase Space ◽  
Linear Theory ◽  
Star Clusters ◽  
Spherical Geometry ◽  
Stellar Model ◽  
Physical Processes ◽  
Loss Cone ◽  
Notable Change

ABSTRACT According to our previous theoretical findings, physical processes in centres of galaxies, star clusters, and the Oort comet cloud can be significantly altered by a new so-called ‘gravitational loss-cone instability’. Using N-body simulations of a spherical stellar model in the dominating Keplerian potential, we confirm the possibility of the instability and go beyond the linear theory. Unlike most other instabilities, the new one shows no notable change in spherical geometry of the cluster, but it significantly accelerates the speed of diffusion of particles in phase space leading to a repopulation of the loss cone and early instability saturation.

scholarly journals Simulation of the loss-cone instability in spherical systems – I. Dominating harmonic potential

2019 ◽  
Vol 492 (1) ◽  
pp. 645-650 ◽  
Author(s):  
E V Polyachenko ◽  
P Berczik ◽  
A Just ◽  
I G Shukhman
Keyword(s):  
Perturbation Theory ◽  
Star Clusters ◽  
Spherical Geometry ◽  
Oort Cloud ◽  
Harmonic Potential ◽  
Linear Perturbation ◽  
Stellar Systems ◽  
Physical Processes ◽  
Loss Cone ◽  
Linear Perturbation Theory

ABSTRACT A new so-called ‘gravitational loss-cone instability’ in stellar systems has recently been investigated theoretically in the framework of linear perturbation theory and proved to be potentially important in understanding the physical processes in centres of galaxies, star clusters, and the Oort Cloud. Using N-body simulations of a toy model, we confirm previous findings for the dominating harmonic potential and go beyond the linear theory. Unlike the well-known instabilities, the new one shows no notable change in the spherical geometry of the cluster, but it significantly accelerates the speed of diffusion of particles in phase space leading to an early instability saturation.

scholarly journals Tests of Evolution Models Using Eclipsing Binaries

1995 ◽  
Vol 10 ◽  
pp. 419-422
Author(s):  
J. Andersen
Keyword(s):  
Chemical Composition ◽  
Star Clusters ◽  
Stellar Model ◽  
Eclipsing Binaries ◽  
Fundamental Parameter ◽  
Fundamental Parameters ◽  
Stellar Models ◽  
Absolute Age ◽  
Cluster Sequence ◽  
Hr Diagram

Stellar models are the means by which we describe and understand the distribution of stars in the HR diagram. A stellar model is, in principle, completely specified by the three fundamental parameters mass, chemical composition, and age. Comparing the properties of models and real stars with the same parameters will tell us if our recipe for constructing stellar models is realistic. Unfortunately, the only star for which all three are known independently of stellar models is the Sun. For stars of other masses and ages we must devise observational tests in which at least one fundamental parameter is unknown. Two such popular test objects are double-lined eclipsing binaries and star clusters.In suitable eclipsing binaries we can determine both masses and chemical composition; the absolute age is unknown, but the same for both stars. Since evolution depends most sensitively on the mass, eclipsing binaries provide a very direct test of the models, but only for two points on a single isochrone. In star clusters, neither ages nor individual masses are known, but the detailed shape and population of a well-observed cluster sequence in the HR diagram provide a number of additional probes into the models.

Phase space complexity of star clusters: Fresh observables for old and new questions

2019 ◽  
Vol 14 (S351) ◽  
pp. 389-394
Author(s):  
Anna Lisa Varri ◽  
Philip G. Breen ◽  
Douglas C. Heggie
Keyword(s):  
Phase Space ◽  
Globular Clusters ◽  
Star Clusters ◽  
Stellar Dynamics ◽  
Stellar Systems ◽  
Internal Dynamics ◽  
The Rich ◽  
Evolving Context ◽  
New Generation ◽  
Precision Astrometry

AbstractThe blooming era of precision astrometry for Galactic studies truly brings the rich internal dynamics of globular clusters to the centre stage. But several aspects of our current understanding of fundamental collisional stellar dynamics cannot match such new-generation data and the theoretical ambitions they trigger. This rapidly evolving context offers the stimulus to address a number of old and new questions concerning the phase space properties of this class of stellar systems.

Quasi-linear theory of the loss-cone instability

1967 ◽  
Vol 1 (1) ◽  
pp. 105-112 ◽  
Author(s):  
A. A. Galeev
Keyword(s):  
Linear Equation ◽  
Free Path ◽  
Linear Theory ◽  
Particle Distribution ◽  
Mean Free Path ◽  
Ion Distribution ◽  
Quasilinear Theory ◽  
Loss Cone ◽  
Small Loss ◽  
The Mean

The loss-cone instability of plasma confined in a mirror-type trap is considered. Relaxation of the particle distribution in the trap with a length larger than the mean free path between ‘turbulent’ collisions is described by conventional quasilinear theory. A quasi-linear equation for the ion distribution is solved analytically for the case of a small loss-cone volume of particles in velocity space (it takes place, for instance, in the case of a trap with a larger mirror ratio).

scholarly journals Monte Carlo Simulations of the 2+1 Dimensional Fokker-Planck Equation: Spherical Star Clusters Containing Massive, Central Black Holes

1985 ◽  
Vol 113 ◽  
pp. 373-413 ◽  
Author(s):  
Stuart L. Shapiro
Keyword(s):  
Black Holes ◽  
Monte Carlo ◽  
Black Hole ◽  
Phase Space ◽  
Star Clusters ◽  
Galactic Nuclei ◽  
Planck Equation ◽  
Time Dependent ◽  
Central Black Hole ◽  
Fokker Planck Equation

The dynamical behavior of a relaxed star cluster containing a massive, central black hole poses a challenging problem for the theorist and intriguing possibilities for the observer. The historical development of the subject is sketched and the salient features of the physical solution and its observational consequences are summarized.The full dynamical problem of a relaxed, self-gravitating, large N-body system containing a massive central black hole has all the necessary ingredients to excite the most dispassionate many-body, computational physicist: it is a time-dependent, multidimensional, nonlinear problem which must be solved over widely disparate length and time scales simultaneously. The problem has been tackled at various levels of approximation over the years. A new 2+1 dimensional Monte Carlo simulation code has been developed in appreciable generality to solve the time-dependent Fokker-Planck equation in E-J space for this problem. The code incorporates such features as (1) a particle “cloning and renormalization” scheme to provide a statistically reliable population of test particles in low density regions of phase space and (2) a time-step “adjustment” algorithm to ensure integration on local relaxation timescales without having to follow typical particles on orbital trajectories. However, critical regions in phase space (e.g. disruption “loss-cone” trajectories) can still be followed on orbital timescales. Numerical results obtained with this Monte Carlo scheme for the dynamical structure and evolution of globular star clusters and dense galactic nuclei containing massive black holes are reviewed.Recent dynamical integrations of the Einstein field equations for spherical, collisionless (Vlasov) systems in General Relativity suggest a possible origin for the supermassive black holes believed to power quasars and active galactic nuclei. This scenario is discussed briefly.

scholarly journals Early-Time Non-Equilibrium Pitch Angle Diffusion of Electrons by Whistler-Mode Hiss in a Plasmaspheric Plume Associated with BARREL Precipitation

2021 ◽  
Vol 8 ◽  
Author(s):  
R. M. Millan ◽  
J.-F. Ripoll ◽  
O. Santolík ◽  
W. S. Kurth
Keyword(s):  
Phase Space ◽  
Pitch Angle ◽  
Particle Interaction ◽  
Phase Space Density ◽  
Angle Distribution ◽  
Loss Cone ◽  
Linear Diffusion ◽  
Whistler Mode ◽  
Space Density ◽  
Van Allen Probes

In August 2015, the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) observed precipitation of energetic (<200 keV) electrons magnetically conjugate to a region of dense cold plasma as measured by the twin Van Allen Probes spacecraft. The two spacecraft passed through the high density region during multiple orbits, showing that the structure was spatial and relatively stable over many hours. The region, identified as a plasmaspheric plume, was filled with intense hiss-like plasma waves. We use a quasi-linear diffusion model to investigate plume whistler-mode hiss waves as the cause of precipitation observed by BARREL. The model input parameters are based on the observed wave, plasma and energetic particle properties obtained from Van Allen Probes. Diffusion coefficients are found to be largest in the same energy range as the precipitation observed by BARREL, indicating that the plume hiss waves were responsible for the precipitation. The event-driven pitch angle diffusion simulation is also used to investigate the evolution of the electron phase space density (PSD) for different energies and assumed initial pitch angle distributions. The results show a complex temporal evolution of the phase space density, with periods of both growth and loss. The earliest dynamics, within the ∼5 first minutes, can be controlled by a growth of the PSD near the loss cone (by a factor up to ∼2, depending on the conditions, pitch angle, and energy), favored by the absence of a gradient at the loss cone and by the gradients of the initial pitch angle distribution. Global loss by 1-3 orders of magnitude (depending on the energy) occurs within the first ∼100 min of wave-particle interaction. The prevalence of plasmaspheric plumes and detached plasma regions suggests whistler-mode hiss waves could be an important driver of electron loss even at high L-value (L ∼6), outside of the main plasmasphere.

The Tropical Madden–Julian Oscillation and the Global Wind Oscillation

2009 ◽  
Vol 137 (5) ◽  
pp. 1601-1614 ◽  
Author(s):  
Klaus Weickmann ◽  
Edward Berry
Keyword(s):  
Phase Space ◽  
Winter Season ◽  
Oscillatory Behavior ◽  
Madden Julian Oscillation ◽  
Physical Processes ◽  
Similar Frequency ◽  
Planetary Scale ◽  
The Pacific ◽  
The Pacific Ocean

Abstract The global wind oscillation (GWO) is a subseasonal phenomenon encompassing the tropical Madden–Julian oscillation (MJO) and midlatitude processes like meridional momentum transports and mountain torques. A phase space is defined for the GWO following the approach of Wheeler and Hendon for the MJO. In contrast to the oscillatory behavior of the MJO, two red noise processes define the GWO. The red noise spectra have variance at periods that bracket 30–60 or 30–80 days, which are bands used to define the MJO. The correlation between the MJO and GWO is ∼0.5 and cross spectra show well-defined, coherent phase relations in similar frequency bands. However, considerable independent variance exists in the GWO. A basic dynamical distinction occurs in the direction of midlatitude wave energy dispersion, being predominantly meridional during a MJO and zonal during the GWO. This is primarily a winter season feature centered over the Pacific Ocean. A case study during April–May 2007 focuses on the GWO and two ∼30-day duration orbits with extreme anomalies in GWO phase space. The MJO phase space projections for the same time were irregular and, it is argued, partially driven by mountain torques and meridional transports. The case study reveals that multiple physical processes and time scales act to create slowly evolving planetary-scale circulation and tropical convection anomalies.

scholarly journals Formation and Disruption of Globular Star Clusters

2002 ◽  
Vol 207 ◽  
pp. 566-576 ◽  
Author(s):  
S. Michael Fall ◽  
Qing Zhang
Keyword(s):  
Globular Clusters ◽  
Star Clusters ◽  
Mass Function ◽  
Star Cluster ◽  
Weak Dependence ◽  
Host Galaxies ◽  
Physical Processes ◽  
Cluster Systems ◽  
Luminosity Functions ◽  
Characteristic Mass

In the first part of this article, we review observations of the mass and luminosity functions of young and old star cluster systems. We also review some of the physical processes that may determine the characteristic mass of globular clusters and the form of their mass function. In the second part of this article, we summarize our models for the disruption of clusters and the corresponding evolution of the mass function. Much of our focus here is on understanding why the mass function of globular clusters has no more than a weak dependence on radius within their host galaxies.

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