Astronomy

The investigation of entropy variation during the star formation process within collapsing molecular clouds represents a significant field of inquiry in astrophysics. As the cloud contracts, the presence of gaseous components contributes to an increase in entropy; however, the degree of this entropy change is contingent upon the spatial constraints imposed on the gases. In this research endeavor, I perform a comprehensive analysis of entropy dynamics on a microcosmic level within the contracting cloud, adhering to the tenets of the second law of thermodynamics. The initial focus centers on a turbulent cloud consisting of N particles, each with a mass of M, which succumbs to gravitational forces. It becomes evident that for the collapse to transpire, the gravitational energy must surpass the opposing pressure forces, resulting in the swift movement of particles throughout the cloud and ultimately facilitating a shift in entropy. Full article

For the deconfinement phase of an SU(2) Yang–Mills theory, we compute the axion mass $m_A$ by appealing to the Veneziano–Witten formula. The topological susceptibility $\chi$ arises (i) from a precisely computable thermal ground-state contribution due to a center of a relevant (anti)caloron, and (ii) from contributions due to free thermal quasi-particles in the effective theory. Both (i) and (ii) are derived by using standard Euclidean thermal field theory techniques. While contribution (i) is positive and $\propto T^4$, contribution (ii) is negative, as demanded by reflection positivity, but negligible compared to contribution (i). As a consequence, practically from the critical temperature $T_c$ onward, a real-valued axion mass $m_A\left(T\right)=\sqrt{{\displaystyle \frac{2}{3}}}\pi {\displaystyle \frac{T^2}{M_P}}$ emerges when the Peccei–Quinn scale is assumed to be the Planck mass $M_P$, independently of the Yang–Mills scale that the axion associates with. We discuss why our results deviate from those found in the dilute instanton gas and interacting instanton liquid approximations, and from results obtained in lattice simulations. Assuming the universe is dark sector to be based on such ultralight axion species, which are nonrelativistic for $T\ll M_P$, we investigate the cosmological conditions for their global Bose condensation as the very early universe cooled to temperatures of the order of ${10}^9$eV. Full article

To investigate the gravitational effects of massive objects on a typical observer, we studied the dynamics of a test particle following ${\mathrm{BMS}}_3$ geodesics. We constructed the ${\mathrm{BMS}}_3$ framework using the canonical phase space formalism and the corresponding Hamiltonian. We focused on analyzing these effects at fine scales of spacetime, which led us to quantization of the phase space. By deriving and studying the solutions of the quantum equations of motion for the test particle, we obtained its energy spectrum and explored the behavior of its wave function. These findings offer a fresh perspective on gravitational interactions in the context of quantum mechanics, providing an alternative approach to traditional quantum field theory analyses. Full article

Archival XMM and ROSAT X-Ray data are used to investigate the structure of the Abell 548–Abell 3367 region. Based on previous optical studies, this is a region likely to be rich in structure, although studies are in disagreement regarding the connection between Abell 3367 and Abell 548. We use the available archival X-Ray data together with kinematic data of counterpart galaxies to address this question and determine the structure in this region. The region is particularly rich in X-Ray structure elongated along a SW-NE axis and consisting of numerous extended X-Ray sources. In general, the structure consists of many galaxy groups and clusters which appear segregated in X-Ray luminosity, with the least luminous ~30% toward the outer region of the clusters, possibly tracing a filament. We find evidence to suggest a supercluster of three clusters at redshifts ~0.04, 0.045, and 0.06. Several of the X-Ray sources coincident with Abell 3367 have counterpart galaxy redshifts consistent with Abell 548, while others are significantly higher. This supports the formation of a supercluster consisting of Abell 548 and Abell 3667, with the higher-redshift X-Ray source being a background object. In addition, they are part of a larger structure consisting of a previously identified cluster at redshift 0.04 and two groups at redshift ~0.06. There is also filamentary structure at z ~0.103. The ubiquity of groups in the large-scale structure suggests that they provide an environment where galaxies are in close proximity and evolution via interaction can proceed well before the galaxies make their way into the dense central region of a cluster. Full article

We present a model-independent method for separating the spectral counterparts of the active galactic nucleus (AGN) NGC 1275 from the surrounding emission of the Perseus cluster, as observed by Suzaku/XIS cameras. The Perseus cluster emission extends to higher energies than typically observed in AGN environments, reaching up to 9–10 keV. This necessitates precise separation of AGN and cluster spectra. To circumvent the degeneracy arising from numerous spectral fitting parameters, including elemental abundances, thermal and Compton emissions from the nucleus, and spectral parameters of the jet synchrotron self-Compton/inverse Compton emissions, we avoid traditional spectral fitting methods. Instead, we leverage spatial resolution and employ a double background subtraction approach. We apply this procedure to the complete set of Suzaku/XIS observational data for NGC 1275, resulting in cleaned spectra and a light curve of the AGN emission in this system. To demonstrate the applicability of our method, we also utilize the available XMM-Newton/EPIC data. Full article

We embed an object with a singular horizon structure, reminiscent of (but fundamentally different from, except in a limiting case) a black hole event horizon, in an expanding, spherically symmetric, homogeneous, Universe that has a positive cosmological constant. Conformal representation is discussed. There is a temperature/pressure singularity and a corresponding scalar curvature singularity at the horizon. The expanding singular horizon ultimately bounds the entire spacetime manifold. It is is preceded by an expanding light front, which separates the spacetime affected by the singularity from that which is not yet affected. An appropriately located observer in front of the light front can have a Hubble–Lemaître constant that is consistent with that currently observed. Full article

Inthe present paper, we investigate neutral current (NC) antineutrino scattering with the constituents of neutron star (NS) matter at zero temperature. The modeling of standard matter in NS is constructed within the framework of both extended relativistic mean-field (E-RMF) and nonrelativistic Korea-IBS-Daegu-SKKU energy density functional (KIDS-EDF) models. In the E-RMF model, we use a new parameter, G3(M), which was constrained by the recent PREX II experiment measurement of neutron distribution in ²⁰⁸Pb, while the KIDS-EDF models are constrained by terrestrial experiments, gravitational-wave signals, and astrophysical observations. Using both realistic and well-constrained matter models, we then calculate the antineutrino differential cross-section (ADCS) and antineutrino mean free path (AMFP) for the interaction between antineutrinos and neutron star (NS) matter constituents using linear response theory. It is found that the AMFP for the KIDS0 and KIDSA models are smaller compared to the SLy4 model and the E-RMF model with the G3(M) parameter. The AMFP result of the Skyrme model with the SLy4 parameter set is found to have a prediction almost similar to that of the E-RMF model with the G3(M) parameter. Contributions of each nucleon to the total AMFP are also presented for the G3(M) model. Full article

Recent discoveries of massive galaxies existing in the early universe, as well as apparent anomalies in Ω_m and H₀ at high redshift, have raised sharp new concerns for the ΛCDM model of cosmology. Here, we address these problems by using new solutions for the Einstein field equations of relativistic compact objects originally found by Ni. Applied to the universe, the new solutions imply that the universe’s mass is relatively concentrated in a thick outer shell. The interior space would not have a flat, Minkowski metric, but rather a repulsive gravitational field centered on the origin. This field would induce a gravitational redshift in light waves moving inward from the cosmic shell and a corresponding blueshift in waves approaching the shell. Assuming the Milky Way lies near the origin, within the KBC Void, this redshift would make H₀ appear to diminish at high redshifts and could thus relieve the Hubble tension. The Ni redshift could also reduce or eliminate the requirement for dark energy in the ΛCDM model. The relative dimness of distant objects would instead arise because the Ni redshift makes them appear closer to us than they really are. To account for the CMB temperature–redshift relation and for the absence of a systematic blueshift in stars closer to the origin than the Milky Way, it is proposed that the Ni redshift and blueshift involve exchanges of photon energy with a photonic spacetime. These exchanges in turn form the basis for a cosmic CMB cycle, which gives rise to gravity and an Einsteinian cosmological constant, Λ. Black holes are suggested to have analogous Ni structures and gravity/Λ cycles. Full article

We present our results on two Z Cam stars: Z Cam and AT Cnc. We apply observational data for the periods that cover the states of outbursts and standstills, which are typical for this type of object. We report an appearance of periodic oscillations in brightness during the standstill in AT Cnc, with small-amplitude variations of 0.03–0.04 mag and periodicity of ≈20–30 min. Based on the estimated dereddened color index (B − V)₀, we calculate the color temperature for both states of the two objects. During the transition from the outburst to the standstill state, Z Cam varies from bluer to redder, while AT Cnc stays redder in both states. We calculate some of the stars’ parameters as the radii of the primary and secondary components and the orbital separation for both objects. We construct the profiles of the effective temperature in the discs of the two objects. Comparing the parameters of both systems, we see that Z Cam is definitely the hotter object and we conclude that it has a more active accretion disc. Full article

In astronomy, understanding the evolutionary trajectories of galaxies necessitates a robust analysis of their star formation histories (SFHs), a task complicated by our inability to observe these vast celestial entities throughout their billion-year lifespans. This study pioneers the application of the Kullback–Leibler Importance Estimation Procedure (KLIEP), an unsupervised domain adaptation technique, to address this challenge. By adeptly applying KLIEP, we harness the power of machine learning to innovatively predict SFHs, utilizing simulated galaxy models to forge a novel linkage between simulation and observation. This methodology signifies a substantial advancement beyond the traditional Bayesian approaches to Spectral Energy Distribution (SED) analysis, which are often undermined by the absence of empirical SFH benchmarks. Our empirical investigations reveal that KLIEP markedly enhances the precision and reliability of SFH inference, offering a significant leap forward compared to existing methodologies. The results underscore the potential of KLIEP in refining our comprehension of galactic evolution, paving the way for its application in analyzing actual astronomical observations. Accompanying this paper, we provide access to the supporting code and dataset on GitHub, encouraging further exploration and validation of the efficacy of the KLIEP in the field. Full article

Gravitational waves produced by binary neutron star mergers offer a unique window into matter behavior under extreme conditions. In this context, we analytically model the effect of matter on gravitational waves from binary neutron star mergers. We start with a binary black hole system, leveraging the post-Newtonian formalism for the inspiral and the Backwards-one-Body model for the merger. We combine the two methods to generate a baseline waveform and we validate our results against numerical relativity simulations. Next, we integrate tidal effects in phase and amplitude to account for matter and spacetime interaction using the NRTidal model and test its accuracy against numerical relativity predictions for two equations of state, finding a mismatch around the merger. Subsequently, we lift the restriction on the coefficients to be independent of the tidal deformability and recalibrate them using the numerical relativity predictions. We obtain better fits for phase and amplitude around the merger and are able to extend the phase modeling beyond the merger. We implement our method in new open-source, user-friendly Python code, steered by a Jupyter Notebook, named RisingTides. Our research offers new perspectives on analytically modeling the effect of tides on the gravitational waves from binary neutron star mergers. Full article

Major (exo)planetary and satellite bodies seem to concentrate at intermediate areas of the radial distributions of all the objects orbiting in each (sub)system. We show that angular-momentum transport during secular evolution of (exo)planets and satellites necessarily results in the observed intermediate accumulation of the massive objects. We quantify the ‘middle’ as the mean of mean motions (orbital angular velocities) when three or more massive objects are involved. Radial evolution of the orbits is expected to be halted when the survivors settle near mean-motion resonances and angular-momentum transfer between them ceases (gravitational Landau damping). This dynamical behavior is opposite in direction to what has been theorized for viscous and magnetized accretion disks, in which gas spreads out and away from either side of any conceivable intermediate area. We present angular momentum transfer calculations in few-body systems, and we also calculate the tidal dissipation timescales and the physical properties of the mean tidal field in planetary and satellite (sub)systems. Full article

Electronically Assisted Astronomy is a fascinating activity requiring suitable conditions and expertise to be fully appreciated. Complex equipment, light pollution around urban areas and lack of contextual information often prevents newcomers from making the most of their observations, restricting the field to a niche expert audience. With recent smart telescopes, amateur and professional astronomers can capture efficiently a large number of images. However, post-hoc verification is still necessary to check whether deep sky objects are visible in the produced images, depending on their magnitude and observation conditions. If this detection can be performed during data acquisition, it would be possible to configure the capture time more precisely. While state-of-the-art works are focused on detection techniques for large surveys produced by professional ground-based observatories, we propose in this paper several Deep Learning approaches to detect celestial targets in images captured with smart telescopes, with a F1-score between 0.4 and 0.62 on test data, and we experimented them during outreach sessions with public in Luxembourg Greater Region. Full article

In this short review, corresponding to a talk given at the conference “Cosmology 2023 in Miramare”, we combine an analysis of five regions observed by H.E.S.S. in the Galactic Center, intending to constrain the Dark Matter (DM) density profile in a WIMP annihilation scenario. For the analysis, we include the state-of-the-art Galactic diffuse emission Gamma-optimized model computed with DRAGON and a wide range of DM density profiles from cored to cuspy profiles, including different kinds of DM spikes. Our results are able to constrain generalized NFW profiles with an inner slope $\gamma \gtrsim 1.3$. When considering DM spikes, the adiabatic spike is completely ruled out. However, smoother spikes given by the interactions with the bulge stars are compatible if $\gamma \lesssim 0.8$, with an internal slope of ${\gamma }_{\mathrm{sp-stars}}=1.5$. Full article

Cosmography, as an integral branch of cosmology, strives to characterize the Universe without relying on pre-determined cosmological models. This model-independent approach utilizes Taylor series expansions around the current epoch, providing a direct correlation with cosmological observations and the potential to constrain theoretical models. Various observable quantities in cosmology can be described as different combinations of cosmographic parameters. Furthermore, one can apply cosmography to models with a varying speed of light. In this case, the Hubble parameter can be expressed by the same combination of cosmographic parameters for both the standard model and varying speed-of-light models. However, for the luminosity distance, the two models are represented by different combinations of cosmographic parameters. Hence, luminosity distance might provide a method to constrain the parameters in varying speed-of-light models. Full article

If visible matter alone is present in the Universe, general relativity (GR) and its Newtonian weak field limit (WFL) cannot explain several pieces of evidence, from the largest to the smallest scales. The most investigated solution is the cosmological model $\mathsf{\Lambda }$ cold dark matter ($\mathsf{\Lambda }$CDM), where GR is valid and two dark components are introduced, dark energy (DE) and dark matter (DM), to explain the ∼70% and ∼25% of the mass–energy budget of the Universe, respectively. An alternative approach is provided by modified gravity theories, where a departure of the gravity law from $\mathsf{\Lambda }$CDM is assumed, and no dark components are included. This work presents refracted gravity (RG), a modified theory of gravity formulated in a classical way where the presence of DM is mimicked by a gravitational permittivity $ϵ\left(\rho \right)$ monotonically increasing with the local mass density $\rho$, which causes the field lines to be refracted in small density environments. Specifically, the flatter the system the stronger the refraction effect and thus, the larger the mass discrepancy if interpreted in Newtonian gravity. RG presented several encouraging results in modelling the dynamics of disk and elliptical galaxies and the temperature profiles of the hot X-ray emitting gas in galaxy clusters and a covariant extension of the theory seems to be promising. Full article

This paper explores the fundamental cosmological principle, with a specific focus on the homogeneity and isotropy assumptions inherent in the Friedmann model that underpins the standard model. We propose a modified redshift model that is based on the spatial distribution of luminous matter, examining three key astronomical quantities: light intensity, number density, and the redshift of galaxies. Our analysis suggests that the model can account for cosmic accelerated expansion without the need for dark energy in the equations. Both simulations and analytical solutions reveal a unique pattern in the formation and evolution of cosmic structures, particularly in galaxy formation. This pattern shows a significant burst of activity between redshifts 0 < z < 0.4, which then progresses rapidly until approximately z ≈ 0.9, indicating that the majority of cosmic structures were formed during this period. Subsequently, the process slows down considerably, reaching a nearly constant rate until around z ≈ 1.6, after which a gradual decline begins. We also observe a distinctive redshift transition around z ≈ 0.9 before the onset of dark-matter-induced accelerated expansion. This transition is directly related to the matter density and is dependent on the geometry of the universe. The model’s ability to explain cosmic acceleration without requiring fine tuning of the cosmological constant highlights its novelty, providing a fresh perspective on the dynamic evolution of the universe. Full article

The notion of a local inertial reference frame is thoroughly analyzed. Dynamics of a field of such frames is derived from the variational principle. It is shown that the resulting theory splits naturally into three sectors, one of which is purely gravitational. Field dynamics in this sector, equivalent to Einstein’s vacuum equations, is obtained unambiguously and admits no ad hoc corrections. The cosmological constant is an essential element of this construction and cannot be removed. It has been shown that the second sector of this theory corresponds to electrodynamics, while the last sector could possibly describe dark matter. Full article

The GINGER (gyroscopes in general relativity) project foresees the construction of an array of large frame ring laser gyroscopes, rigidly connected to the Earth. Large frame ring laser gyroscopes are high-sensitivity instruments used to measure angular velocity with respect to the local inertial frame. In particular, they can provide sub-daily variations in the Earth rotation rate, a measurement relevant for geodesy and for fundamental physics at the same time. Sensitivity is the key point in determining the relevance of this instrument for fundamental science. The most recent progress in sensitivity evaluation, obtained on a ring laser prototype, indicates that GINGER should reach the level of 1 part in ${10}^{11}$ of the Earth’s rotation rate. The impact on fundamental physics of this kind of apparatus is reviewed. Full article