New Astronomy最新文献

This paper is devoted to the study of curvature properties of Hayward black hole (briefly, HBH) spacetime, which is a solution of Einstein field equations (briefly, EFE) having non-vanishing cosmological constant. We have proved that the HBH spacetime is an Einstein manifold of level 2, 2-quasi Einstein, generalized quasi-Einstein and Roter type manifold. Also, it is shown that the nature of the HBH spacetime is pseudosymmetric and it obeys several types of pseudosymmetries, such as, pseudosymmetry due to concircular, conformal and conharmonic curvature (i.e., $F\cdot F=LQ(g,F)$ for $F=W,C,K$ with a smooth scalar function $L$), and it also possesses the relation $R\cdot R-LQ(g,C)=Q(S,R)$. It is engrossing to mention that the nature of energy momentum tensor of the HBH spacetime is pseudosymmetric. On the basis of curvature related properties, we have made a comparison among Reissner–Nordström spacetime, interior black hole spacetime and HBH spacetime. It is noteworthy to mention that the gravitational force of the point-like global monopole spacetime is much stronger than that of HBH spacetime. Also, it is shown that the HBH spacetime admits an almost $\eta$-Ricci soliton as well as an almost $\eta$-Ricci-Yamabe soliton. Finally, an elegant comparative study is delineated between the HBH spacetime and the point-like global monopole spacetime with respect to different kinds of symmetry, such as, motion, curvature collineation, curvature inheritance etc.

Properties of molecular clouds ($MCs$) lying in our Galaxy and their star formation scenarios have been investigated with the help of multivariate unsupervised machine learning techniques concerning several observable parameters. At first, the $MCs$ have been classified into four coherent groups using the standard K-means clustering method. Subsequently, the optimum number of groups has been estimated by applying the Elbow method as well as the computation of Silhouette widths for a robustness check. Later, the properties of the groups are studied through several observable parameters as mentioned along with computed ones e.g. star formation rates ($SFRs$), virial masses, mass-spectra, dynamical time scales ($T_d$), etc. to get a deeper understanding of the star formation process and dynamical evolution of these clouds. It is found that cluster 1 is suitable for the formation of field stars, binary pairs, or stellar associations, whereas the clouds in cluster 2 and cluster 3 are favorable sites for the formation of Galactic clusters of moderate masses, and cluster 4 may produce massive Galactic clusters as well as a few globular clusters. Surprisingly, for each cluster, clouds at around Galacto-centric radius $\sim$8 kpc, and on the near Galactic plane has a significantly low $SFR$. These occurrences indicate that the star formation phenomenon has yet not started or the proneness to start in that region.

This manuscript examines how effective matter variables influence the geometry of compact stellar objects with anisotropic matter configuration in modified $f(R,\phi ,\chi )$ gravity, where $R$ represents the Ricci scalar, $\phi$ is the scalar field and $\chi$ is a kinetic term depending on the scalar field. The unknown constants in the metric potentials are determined by the smooth matching of an interior region with the exterior spacetime. We then check the viability of some selected stars through various physical quantities, i.e., effective matter contents, anisotropy and energy constraints. We also examine the equilibrium and stable states through the Tolman–Oppenheimer–Volkoff equation and sound speed/adiabatic index, respectively. This comprehensive analysis ensures that viable and stable compact stars exist in this modified theory as all the necessary conditions are satisfied.

We analyze $H\left(z\right)$ parameter data with some conditions by using Lagrange mean value theorem in Calculus. We find that: (1) there exists decelerated phase at 1 $\sigma$ confidence level in the redshift range $(0.38,0.59)$; (2) the equation of state of dark energy may be less than $-1$ at 1 $\sigma$ confidence level at some redshifts in the redshift range $(1.3,1.53)$; (3) there exists accelerated phase at 1 $\sigma$ confidence level in the redshift range $(1.037,1.944)$. These results may provide possible evidences for physics beyond $\Lambda$CDM.

In this work, we calculate the S-factor for $p+$⁹Be Radiative Capture Reaction according to a modified potential model. We consider the sum of all possible electrical and magnetic transitions as a total cross-section. The zero-energy $S$-factor results are in good agreement with previously theoretical studies and the experimentally reported data.

We present the result of over 50-h of Johnson-B photometric observation of HD 137949. These high-speed photometric data were acquired between June 12 and August 19 2013 using the 0.5-m telescope of the South African Astronomical Observatory (SAAO). The result of our frequency analysis when compared with that of similar B-light photometric data obtained in 1981 and 1987 using the same telescope reveals the existence of a long-term stability in its principal frequency of oscillation at ${\nu }_1=2.014781\pm 0.000003$ mHz; even with the excitation of two new secondary oscillations (${\nu }_2=2.016787\pm 0.000006$ mHz; ${\nu }_3=2.012628\pm 0.000009$ mHz). On the contrary, the signature of its principal amplitude of oscillation ($A$) was found to have changed drastically within a time-span of about three decades. However, the aggregate amplitude ($\sum A$) of all the detected oscillations was observed to have remained constant within the period under investigation. In addition, HD 137949 was observed to have undergone pulsational energy re-distribution within this time-span of about three decades; with a signature that is suggestive of non-conservation of its total energy (pulsational). We discuss the possible implications of the recently observed dynamics in the oscillation-signature of HD 137949.

This paper investigates motion and zero velocity curves of a dust grain around collinear libration points (CLPs) of the circular restricted three-body problem (R3BP) when both stars IRAS 11472-0800 and G29-38 vary their masses according to the unified Mestschersky law (UML) and their motion is described by the Gylden-Mestschersky problem (GMP) with further assumption that the bigger body is a variable triaxial star. The non-autonomous equations of motion of the model are derived and transformed to the autonomized forms using the Mestschersky transformation (MT), the UML, the particular integral and solutions of the GMP, and a transformation we introduced which enable us to convert the time dependent triaxiality of the bigger star to constant triaxiality. The CLPs are examined and it is seen that when motion takes place on the plane joining the stars, there are three CLPs. To further validate the existence of the CLPs, we obtain three polynomial equations of degree seven for the three CLPs, respectively and we numerically explored the roots. It is seen that only three CLPs exists for all values of the mass parameters coupled with triaxiality of the bigger star. The stability of these points is studied and it is seen that CLPs$L_1$ and$L_2$ are unstable for all mass parameters throughout the interval $0<\kappa <\infty$, where$\kappa$ is a constant of the particular integral of the GMP and depicts the mass variation parameter of the stars. However, CLP$L_3$can be stable and unstable due to the triaxiality of the bigger star, mass parameters and the mass variation parameter. Further, the zero velocity curves (ZVCs) of the dust grain around the CLPs are investigated and the effects of the system parameters divulged. It is seen that, the mass parameters and mass variation parameter can increase or decrease the region where motion of the dust grain is dynamically forbidden, while triaxiality of the bigger star increases the region where motion is forbidden around the CLPs and it allows the appearance of a petal-shaped ZVC around the bigger star. Finally, the orbits of the dust grain around the CLPs is explored, and it is seen that the paths around each collinear point differs. The deviations in the paths are due to the perturbing effects of the mass parameters, triaxiality of the bigger star and the mass variation parameter of the stars. Our problem could have important physical applications when studying celestial bodies of triaxial shape with changing masses of the bodies. In particular, we can assume that the binary system may describe a host star along with an exoplanet, or a massive exoplanet with an exomoon whose masses vary with time.

In this paper, we aim to showcase the significant impacts of albedo and eccentricity of the primaries on the infinitesimal mass within the elliptic case of the Sitnikov five-body problem. The Van der Pol transformation and averaging technique were employed to formulate the averaged equations of motion for the infinitesimal mass. Subsequently, the Hamiltonian equations of motion were derived using the action angle variables $I$ and $\theta$. Additionally, we obtained $\theta$ in terms of the Jacobi elliptic function $sn$ through a canonical transformation. The investigation utilized the first return map to explore various orbits such as regular, periodic, quasi-periodic, chaotic, or stochastic in the presence of albedo and eccentricity. It was observed that chaotic and stochastic regions emerged as the albedo effect increased, disrupting the periodic tubes and islands. Moreover, by escalating the albedo effect and eccentricity of the primaries, several families of periodic orbits were revealed.

Gravitational microlensing is known to be an impressive tool for searching dark, small, and compact objects that are missed by the usual astronomical observations. In this paper, by analysing multiple images acquired by DECam, we present the detection and a complete description of the microlensing event LMC J05074558-65574990 which is most likely due to a sub-solar object with mass $(0.16\pm 0.10)$ M${}_{\odot }$, hence in the mass range between a massive brown dwarf and a red dwarf, whose distance is estimated to be $7.8_{-3.4}^{+4.1}\times 10^2$ pc thanks to the Gaia observation of the source, leading us to consider this lens as one the closest ever detected.