Astronomische Nachrichten最新文献

We investigate the emission of gravitational waves from spheroidal magnetized strange stars in two scenarios: an isolated, slowly rotating star and a binary system. For the isolated star, we compute the quadrupole moment and the amplitude of the gravitational waves that may be emitted. In the case of the binary system, we determine the tidal deformation by simultaneously solving the spheroidal structure equations and the Love number equation. Our results are compared with data inferred from the GW170817 event, which is also used to estimate the mass and tidal deformation of the companion star in the binary system. Our model supports the existence of binary systems formed by magnetized strange stars, predicting gravitational wave signals consistent with other models of binary systems composed of magnetized hadronic stars or non-magnetized quark stars.

This review provides a comprehensive discussion of Gauss–Bonnet (GB) gravity, a gravitational theory incorporating higher-order curvature corrections, which can influence gravitational dynamics in higher dimensions. We explore the fundamental motivation for introducing the GB term, particularly in the context of high-energy physics and string theory-inspired scenarios, highlighting its potential in addressing key issues such as singularities, the nature of dark energy, cosmic acceleration, modifications to neutron stars and black holes, and cosmological singularities. Furthermore, we examine emerging research directions and recent advancements in the field, including torsion effects, compact astrophysical phenomena, and modified Gauss–Bonnet models, which further expand the applications of GB gravity in modern theoretical physics and cosmology.

Pulsars, characterized as highly magnetized and rapidly rotating neutron stars, offer a unique laboratory for probing physics under extreme conditions. Magnetars, a subclass of pulsars powered by magnetic field energy, exhibit quantized and highly degenerate Landau levels for relativistic electrons in their crustal ultrastrong magnetic fields. The energy difference between these Landau levels and the field-free system determines the magnetic susceptibility. We first review spin degrees of freedom in relativistic electrons and magnetization mechanisms, then employ quantum statistical methods to calculate the magnetic susceptibility of relativistic electron gases in magnetar crusts. Finally, numerical simulations for the paramagnetic susceptibility oscillatory in superhigh magnetic fields in the magnetar crust was performed. Our results reveal that the magnetization under ultrastrong fields demonstrates oscillatory behavior analogous to the de Haas–van Alphen effect observed in certain low-temperature metals. The total susceptibility, $��\chi �$, comprises a non-oscillatory component ($��{\chi }_m�$) and an oscillatory term ($��{\tilde{\chi }}_m�$), where higher harmonic amplitudes of the oscillatory susceptibility grow with increasing electron density. Notably, the total paramagnetic susceptibility of electrons near the crust-core boundary does not exceed the critical magnetization threshold. However, if an ultrastrong magnetic field exists in the neutron star core, the susceptibility of the electron gas could surpass this critical value, suggesting the potential occurrence of non-equilibrium magnetization processes. This implies a first-order phase transition, akin to gas–liquid transitions, leading to coexisting stable magnetization states or metastable supercooled magnetic phases. A sudden transition from metastable to stable states may release stored magnetic energy, offering a plausible explanation for the observed excess radiation during magnetar giant flares.

This review discusses the thermal evolution of neutron star crusts, focusing on recent advancements in cooling models, superfluidity, and surface composition. The cooling process primarily occurs through neutrino radiation and thermal conduction, with the surface temperature of young neutron stars remaining stable for about 100 years before the internal temperature gradually decreases. The paper also discusses challenges such as uncertainties in the equation of state and limited observational data. By bridging the gap between theoretical predictions and observational data, this review aims to deepen our understanding of the thermal evolution of neutron stars.

The mode switching of PSR J0742-2822 at 3.1 GHz was investigated using single-pulse data from the Parkes 64-m radio telescope in Australia. By analyzing the ratio of the relative intensity of the two components for each sub-integral profile, we classified the integral profile of this source into two modes: normal mode and abnormal mode. We then obtained the average profile of PSR J0742-2822 at 3.1 GHz for each mode. The results indicate that the normal and abnormal modes of integrated pulse profiles occurred 72% and 28% of the time, respectively, over a total of 3.7 h of observation. This study is significant for understanding the theoretical mechanism behind the pulsar mode-switching phenomenon.

Fast Radio Bursts (FRBs) are mysterious, short-duration bursts of radio waves originating from cosmological distance. This paper explores various properties of FRBs, such as Dispersion Measure (DM), Rotation Measure (RM), pulse width, duration, redshift distribution, and spectral index. The paper also introduces our recent research on FRB host galaxies and event rate density, focusing on recalculating event rate densities using sources discovered by CHIME/FRB. This review underscores the importance of continued research to unravel the mysteries of FRBs and their diverse properties.

The analysis of equations of state models, which describe the matter inside neutron stars, contributes to the understanding of two fundamental pillars of physics, nuclear matter and gravitation. Recent astrophysical observations such as the event titled GW170817, which founded the era of multi-messenger observations, as well as the important measurements established by the Neutron Star Interior Composition Explorer (NICER) of the radius and mass of the compact objects PSR J0030 + 0451 and PSR J0740 + 6620 brought new perspectives on the limitations and inconsistencies between observational data and predictions through the gravity model. Combining the current motivating scenario with the growth of available data and increased computational capacity, the topic has been expanded with the addition of new tools based on machine learning, which have evolved considerably since the mid-2010s. Seeking to contribute to the understanding through a simple and effective representation while maintaining robustness and reliability of its results among the range of complex models existing in the literature, the work under analysis focuses on the application of deep neural networks in the generalization of neutron star state equations, exploring the bases theories of generalized piecewise polytropic formalism, and the construction of a model whose learning method is based on Bayesian probability.

UTC(k) can be considered a shorthand for the local time standard maintained by a country's or region's time- frequency laboratory. Each lab uses its local atomic clocks to maintain this standard and synchronizes it with Coordinated Universal Time (UTC). Although local atomic clocks can operate independently, they generally rely on UTC as a reference standard for precision and long-term stability. To effectively monitor local atomic clocks and improve monitoring efficiency, this paper aims to study new monitoring methods from the perspective of macroscopic astrometry. By utilizing the measurement results of millisecond pulsars and combining them with clock models, this paper focuses on calculating and predicting the deviation data of local atomic clocks. This method not only expands the means of monitoring local atomic clocks but also has significant implications for improving monitoring accuracy and reliability. To validate its effectiveness, we first calculate and analyze the actual and simulated data of millisecond pulsars, then compare the analysis results with the conventional clock deviation data of local clocks based on UTC as a reference. The results indicate that using millisecond pulsars for monitoring can feasibly obtain the phase and frequency deviations of local atomic clocks within a 95% confidence interval. This demonstrates the feasibility of this method. Therefore, monitoring local atomic clocks using millisecond pulsars is reliable and effective. This study provides new insights and methods for the monitoring of local clocks and is significant for improving monitoring accuracy and reliability.