MDPI - Publisher of Open Access Journals

29 pages, 6369 KiB

Open AccessArticle

Keplerian Ringed-Disk Viscous-Diffusive Evolution and Combined Independent General Relativistic Evolutions

by Daniela Pugliese, Zdenek Stuchlík and Vladimir Karas

Universe 2025, 11(3), 88; https://doi.org/10.3390/universe11030088 - 6 Mar 2025

Viewed by 566

We investigate the evolution of a set of viscous rings, solving a diffusion-like evolution equation in the (Keplerian disk) Newtonian regime. The Lynden-Bell and Pringle approach for a single disk regime is applied to a disk with a ring profile mimicking a set of orbiting viscous rings. We discuss the time evolution of the disk, adopting different initial wavy (ringed) density profiles. Four different stages of the ring-cluster evolution are distinguished. In the second part of this analysis, we also explore the general relativistic framework by investigating the time evolution of composed systems of general relativistic co-rotating and counter-rotating equatorial disks orbiting a central Kerr black hole for faster spinning and slowly spinning black holes. In the sideline of this analysis, we consider a modified viscosity prescription mimicking an effective viscosity in the general relativistic ring interspace acting in the early phases of the rings’ evolutions, exploring the double system dynamics. Each ring of the separate sequence spreads inside the cluster modifying its inner structure following the rings merging. As the original ringed structure disappears, a single disk appears. The final configuration has a (well-defined) density peak, and its evolution turns in the final stages are dominated by its activity at the inner edge. Full article

(This article belongs to the Section Gravitation)

► Show Figures

Figure 1

13 pages, 3218 KiB

Open AccessArticle

Source Count Distribution of Fermi LAT Gamma-Ray Blazars Using Novel Nonparametric Methods

by Xuhang Yin and Houdun Zeng

Universe 2024, 10(9), 340; https://doi.org/10.3390/universe10090340 - 26 Aug 2024

Cited by 1 | Viewed by 1040

Abstract

We utilized a sample from the Fermi-LAT 14-year Source Catalog by adjusting the flux detection threshold, enabling us to derive the intrinsic source count distribution

d N / d F_{25}

of extragalactic blazars using nonparametric, unbinned methods developed by Efron and Petrosian [...] Read more.

We utilized a sample from the Fermi-LAT 14-year Source Catalog by adjusting the flux detection threshold, enabling us to derive the intrinsic source count distribution

d N / d F_{25}

of extragalactic blazars using nonparametric, unbinned methods developed by Efron and Petrosian and Lynden-Bell. Subsequently, we evaluated the contribution of blazars to the extragalactic gamma-ray background. Our findings are summarized as follows: (1) There is no significant correlation between flux and spectral index values among blazars and their subclasses FSRQs and BL Lacs. (2) The intrinsic differential distributions of flux values exhibit a broken-power-law form, with parameters that closely match previous findings. The intrinsic photon index distributions are well described by a Gaussian form for FSRQs and BL Lacs individually, while a dual-Gaussian model provides a more appropriate fit for blazars as a whole. (3) Blazars contribute 34.5% to the extragalactic gamma-ray background and 16.8% to the extragalactic diffuse gamma-ray background. When examined separately, FSRQs and BL Lacs contribute 19.6% and 13% to the extragalactic gamma-ray background, respectively. Full article

(This article belongs to the Special Issue Focus on Active Galactic Nuclei)

► Show Figures

Figure 1

15 pages, 3243 KiB

Open AccessFeature PaperArticle

A Monte Carlo Method for Calculating Lynden-Bell Equilibrium in Self-Gravitating Systems

by Tarcísio N. Teles, Calvin A. F. Farias, Renato Pakter and Yan Levin

Entropy 2023, 25(10), 1379; https://doi.org/10.3390/e25101379 - 25 Sep 2023

Cited by 1 | Viewed by 1442

Abstract

We present a Monte Carlo approach that allows us to easily implement Lynden-Bell (LB) entropy maximization for an arbitrary initial particle distribution. The direct maximization of LB entropy for an arbitrary initial distribution requires an infinite number of Lagrange multipliers to account for the Casimir invariants. This has restricted studies of Lynden-Bell’s violent relaxation theory to only a very small class of initial conditions of a very simple waterbag form, for which the entropy maximization can be performed numerically. In the present approach, an arbitrary initial distribution is discretized into density levels which are then evolved using an efficient Monte Carlo algorithm towards the final equilibrium state. A comparison is also made between the LB equilibrium and explicit Molecular Dynamics simulations. We find that for most initial distributions, relaxation is incomplete and the system is not able to reach the state of maximum LB entropy. In particular, we see that the tail of the stationary particle distribution is very different from the one predicted by the theory of violent relaxation, with a hard cutoff instead of an algebraic decay predicted by LB’s theory. Full article

(This article belongs to the Special Issue Statistical Mechanics of Self-Gravitating Systems)

► Show Figures

Figure 1

Search Results (3)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI

Saved Queries

Search Filter Reset All

Years

Feature Papers

Subjects

Journals

Article Types

Countries / Regions

Search Results (3)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI