Journal Description
Astronomy
Astronomy
is an international, peer-reviewed, open access journal on observational astronomy, theoretical astronomy and other specific subfields published quarterly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus and other databases.
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 27.6 days after submission; acceptance to publication is undertaken in 7.6 days (median values for papers published in this journal in the first half of 2025).
- Recognition of Reviewers: APC discount vouchers, optional signed peer review, and reviewer names published annually in the journal.
- Astronomy is a companion journal of Universe and Aerospace.
Latest Articles
The Status of the Astrophysical Parameters of Upper Main Sequence Stars
Astronomy 2025, 4(3), 15; https://doi.org/10.3390/astronomy4030015 - 22 Aug 2025
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Calibrating the ages, masses, and radii of stars on the upper main sequence depends heavily on accurate measurements of the effective temperature ( ) and surface gravity ( ). These parameters are difficult to obtain meticulously due to the
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Calibrating the ages, masses, and radii of stars on the upper main sequence depends heavily on accurate measurements of the effective temperature ( ) and surface gravity ( ). These parameters are difficult to obtain meticulously due to the nature of hot stars, which exhibit features such as rapid rotation, atomic diffusion, pulsation, and stellar winds. We compare the and values of apparent normal B-F stars in four recent catalogues that employ different methods and pipelines to obtain these parameters. We derived various statistical parameters to compare the differences between the catalogues and discussed the astrophysical implications of these differences. Our results show that the huge differences in (up to K) and (up to 2 dex) between the catalogues have serious implications on the determination of ages, masses, and radii of the stars in question. We conclude that there appears to be no homogeneous set of stellar parameters on the upper main sequence, and one must be cautious when interpreting results obtained from using only one of the catalogues. The homogenisation of said parameters is an essential task for the future and will have a significant impact on astrophysical research dealing with stars on the upper main sequence.
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Open AccessArticle
Gravity Wave Phase Shift in a Cold Quark Star with a Nonconvex QCD BZT Shock Wave Van Der Waals Equation of State
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Keith Andrew, Eric V. Steinfelds and Kristopher A. Andrew
Astronomy 2025, 4(3), 14; https://doi.org/10.3390/astronomy4030014 - 22 Aug 2025
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We investigate BZT shocks and the QCD phase transition in the dense core of a cold quark star in beta equilibrium subject to the multicomponent van der Waals (MvdW) equation of state (EoS) as a model of internal structure. When this system is
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We investigate BZT shocks and the QCD phase transition in the dense core of a cold quark star in beta equilibrium subject to the multicomponent van der Waals (MvdW) equation of state (EoS) as a model of internal structure. When this system is expressed in terms of multiple components, it can be used to explore the impact of a phase transition from a hadronic state to a quark plasma state with a complex clustering structure. The clustering can take the form of colored diquarks or triquarks and bound colorless meson, baryon, or hyperon states at the phase transition boundary. The resulting multicomponent EoS system is nonconvex, which can give rise to Bethe–Zel’dovich–Thompson (BZT) phase-changing shock waves. Using the BZT shock wave condition, we find constraints on the quark density and examine how this changes the tidal deformability of the compact core. These results are then combined with the TOV equations to find the resulting mass and radius relationship. These states are compared to recent astrophysical high-mass neutron star systems, which may provide evidence for a core that has undergone a quark gluon phase transition such as PSR 0943+10 or GW 190814.
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The Use of Conditional Variational Autoencoders in Generating Stellar Spectra
by
Marwan Gebran and Ian Bentley
Astronomy 2025, 4(3), 13; https://doi.org/10.3390/astronomy4030013 - 22 Aug 2025
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We present a conditional variational autoencoder (CVAE) that generates stellar spectra covering 4000 ≤ ≤ 11,000 K, dex, dex,
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We present a conditional variational autoencoder (CVAE) that generates stellar spectra covering 4000 ≤ ≤ 11,000 K, dex, dex, km/s, between 0 and 4 km/s, and for any instrumental resolving powers less than 115,000. The spectra can be calculated in the wavelength range 4450–5400 Å. Trained on a grid of SYNSPEC spectra, the network synthesizes a spectrum in around two orders of magnitude faster than line-by-line radiative transfer. We validate the CVAE on test spectra unseen during training. Pixel-wise statistics yield a median absolute residual of < flux units with no wavelength-dependent bias. A residual error map across the parameters plane shows everywhere, and marginal diagnostics versus , , , , and reveal no relevant trends. These results demonstrate that the CVAE can serve as a drop-in, physics-aware surrogate for radiative transfer codes, enabling real-time forward modeling in stellar parameter inference and offering promising tools for spectra synthesis for large astrophysical data analysis.
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Open AccessArticle
Nonlinearity in Turbulent Diffusion as a Possible Cause of Stellar Flares
by
Elena Popova
Astronomy 2025, 4(3), 12; https://doi.org/10.3390/astronomy4030012 - 7 Jul 2025
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Extremely powerful flares releasing energy well above erg are rare compared to the typical manifestations of solar activity, which are already being routinely monitored by the existing Space Weather network—with some level of predictability. However, much less is known about the
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Extremely powerful flares releasing energy well above erg are rare compared to the typical manifestations of solar activity, which are already being routinely monitored by the existing Space Weather network—with some level of predictability. However, much less is known about the mechanisms behind such rare events (like the well-documented Carrington event of 1859) or about hypothetical superflares that could exceed current energy estimates by several orders of magnitude. We propose a model based on the nonlinear suppression of turbulent diffusion with increasing magnetic field, which ultimately leads to the random occurrence of regions with a magnetic field amplitude significantly exceeding the magnetic field amplitude in a regular cycle. This is similar to the mechanism of a local “explosion of an overheated boiler”. Such regions can be correlated with flares. In our model, flares have different powers.
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Open AccessReview
A Library of 77 Multibody Solar and Extrasolar Subsystems—A Review of Their Dynamical Properties, Global Mean-Motion Resonances, and the Landau-Damped Mean Tidal Fields
by
Dimitris M. Christodoulou, Silas G. T. Laycock and Demosthenes Kazanas
Astronomy 2025, 4(3), 11; https://doi.org/10.3390/astronomy4030011 - 23 Jun 2025
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We revisit 77 relaxed (extra)solar multibody (sub)systems containing 2–9 bodies orbiting about gravitationally dominant central bodies. The listings are complete down to (sub)systems with 5 orbiting bodies and additionally contain 33 smaller systems with 2–4 orbiting bodies. Most of the multiplanet systems (68)
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We revisit 77 relaxed (extra)solar multibody (sub)systems containing 2–9 bodies orbiting about gravitationally dominant central bodies. The listings are complete down to (sub)systems with 5 orbiting bodies and additionally contain 33 smaller systems with 2–4 orbiting bodies. Most of the multiplanet systems (68) have been observed outside of our solar system, and very few of them (5) exhibit classical Laplace resonances (LRs). The remaining 9 subsystems have been found in our solar system; they include 7 well-known satellite groups in addition to the four gaseous giant planets and the four terrestrial planets, and they exhibit only one classical Laplace resonant chain, the famous Galilean LR. The orbiting bodies (planets, dwarfs, or satellites) appear to be locked in/near global mean-motion resonances (MMRs), as these are determined in reference to the orbital period of the most massive (most inert) body in each (sub)system. We present a library of these 77 multibody subsystems for future use and reference. The library listings of dynamical properties also include regular spacings of the orbital semimajor axes. Regularities in the spatial configurations of the bodies were determined from patterns that had existed in the mean tidal field that drove multibody migrations toward MMRs, well before the tidal field was erased by the process of `gravitational Landau damping’ which concluded its work when all major bodies had finally settled in/near the global MMRs presently observed. Finally, detailed comparisons of results help us discern the longest commonly-occurring MMR chains, distinguish the most important groups of triple MMRs, and identify a new criterion for the absence of librations in triple MMRs.
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Open AccessArticle
Core–Corona Decomposition of Very Compact (Neutron) Stars: Accounting for Current Data of XTE J1814-338
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Rico Zöllner and Burkhard Kämpfer
Astronomy 2025, 4(2), 10; https://doi.org/10.3390/astronomy4020010 - 9 Jun 2025
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A core–corona decomposition of compact (neutron) star models was compared with the current mass–radius data of the outlier XTE J1814-338. The corona (which may also be dubbed the envelope, halo or outer crust) is assumed to be of Standard Model matter, with an
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A core–corona decomposition of compact (neutron) star models was compared with the current mass–radius data of the outlier XTE J1814-338. The corona (which may also be dubbed the envelope, halo or outer crust) is assumed to be of Standard Model matter, with an equation of state that is supposed to be faithfully known and accommodates nearly all other neutron star data. The core, solely parameterized by its mass, radius and transition pressure, presents a challenge regarding its composition. We derived a range of core parameters needed to describe the current data of XTE J1814-338.
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Open AccessArticle
Analytic Investigation of the Imprints of Dark Energy and Charge on the Kerr–Newmann–De Sitter Black-Hole Photon Ring
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James Mugambi, Eunice Omwoyo and Dismas Wamalwa
Astronomy 2025, 4(2), 9; https://doi.org/10.3390/astronomy4020009 - 21 May 2025
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In 2019, the Event Horizon Telescope (EHT) released the first image of a black hole, sparking huge interest in the study of black-hole images. We present analytical solutions to the null geodesic equations for Kerr–Newman–de Sitter black holes derived using Jacobi elliptic functions.
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In 2019, the Event Horizon Telescope (EHT) released the first image of a black hole, sparking huge interest in the study of black-hole images. We present analytical solutions to the null geodesic equations for Kerr–Newman–de Sitter black holes derived using Jacobi elliptic functions. Using these solutions, we have performed an analytic ray-tracing simulation to model direct images, lensing rings, and photon rings, considering standard observers and zero angular momentum observers (ZAMOs). Additionally, we have derived analytic expressions for the critical parameters governing the structure of the photon ring and analyzed them in detail. From the foregoing, an increase in charge leads to a decrease in both time delay and Lyapunov exponent, while the change in azimuthal angle is insignificant. These findings improve our understanding of the effects of charge on black-hole photon rings and provide a foundation for future studies.
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Open AccessArticle
At the Edge of Uncertainty: Decoding the Cosmological Constant Value with the Bose–Einstein Distribution
by
Ahmed Farag Ali and Nader Inan
Astronomy 2025, 4(2), 8; https://doi.org/10.3390/astronomy4020008 - 13 May 2025
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We propose that the observed value of the cosmological constant may be explained by a fundamental uncertainty in the spacetime metric, which arises when combining the principle that mass and energy curve spacetime with the quantum uncertainty associated with particle localization. Since the
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We propose that the observed value of the cosmological constant may be explained by a fundamental uncertainty in the spacetime metric, which arises when combining the principle that mass and energy curve spacetime with the quantum uncertainty associated with particle localization. Since the position of a quantum particle cannot be sharply defined, the gravitational influence of such particles leads to intrinsic ambiguity in the formation of spacetime geometry. Recent experimental studies suggest that gravitational effects persist down to length scales of approximately m, while quantum coherence and macroscopic quantum phenomena such as Bose–Einstein condensation and superfluidity also manifest at similar scales. Motivated by these findings, we identify a length scale of spacetime uncertainty, m, which corresponds to the geometric mean of the Planck length and the radius of the observable universe. We argue that this intermediate scale may act as an effective cutoff in vacuum energy calculations. Furthermore, we explore the interpretation of dark energy as a Bose–Einstein distribution with a characteristic reduced wavelength matching this uncertainty scale. This approach provides a potential bridge between cosmological and quantum regimes and offers a phenomenologically motivated perspective on the cosmological constant problem.
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Open AccessArticle
Hilbert Bundles and Holographic Space–Time Models
by
Tom Banks
Astronomy 2025, 4(2), 7; https://doi.org/10.3390/astronomy4020007 - 22 Apr 2025
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We reformulate holographic space–time models in terms of Hilbert bundles over the space of the time-like geodesics in a Lorentzian manifold. This reformulation resolves the issue of the action of non-compact isometry groups on finite-dimensional Hilbert spaces. Following Jacobson, I view the background
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We reformulate holographic space–time models in terms of Hilbert bundles over the space of the time-like geodesics in a Lorentzian manifold. This reformulation resolves the issue of the action of non-compact isometry groups on finite-dimensional Hilbert spaces. Following Jacobson, I view the background geometry as a hydrodynamic flow, whose connection to an underlying quantum system follows from the Bekenstein–Hawking relation between area and entropy, generalized to arbitrary causal diamonds. The time-like geodesics are equivalent to the nested sequences of causal diamonds, and the area of the holoscreen (The holoscreen is the maximal volume (“area”) leaf of a null foliation of the diamond boundary. I use the term area to refer to its volume.) encodes the entropy of a certain density matrix on a finite-dimensional Hilbert space. I review arguments that the modular Hamiltonian of a diamond is a cutoff version of the Virasoro generator of a -dimensional CFT of a large central charge, living on an interval in the longitudinal coordinate on the diamond boundary. The cutoff is chosen so that the von Neumann entropy is up to subleading corrections, in the limit of a large-dimension diamond Hilbert space. I also connect those arguments to the derivation of the ’t Hooft commutation relations for horizon fluctuations. I present a tentative connection between the ’t Hooft relations and currents in the CFTs on the past and future diamond boundaries. The ’t Hooft relations are related to the Schwinger term in the commutator of the vector and axial currents. The paper in can be read as evidence that the near-horizon dynamics for causal diamonds much larger than the Planck scale is equivalent to a topological field theory of the ’t Hooft CR plus small fluctuations in the transverse geometry. Connes’ demonstration that the Riemannian geometry is encoded in the Dirac operator leads one to a completely finite theory of transverse geometry fluctuations, in which the variables are fermionic generators of a superalgebra, which are the expansion coefficients of the sections of the spinor bundle in Dirac eigenfunctions. A finite cutoff on the Dirac spectrum gives rise to the area law for entropy and makes the geometry both “fuzzy” and quantum. Following the analysis of Carlip and Solodukhin, I model the expansion coefficients as two-dimensional fermionic fields. I argue that the local excitations in the interior of a diamond are constrained states where the spinor variables vanish in the regions of small area on the holoscreen. This leads to an argument that the quantum gravity in asymptotically flat space must be exactly supersymmetric.
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Open AccessArticle
Distance to M87 as the Mode of the Modulus Distribution
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Mariusz Tarnopolski
Astronomy 2025, 4(2), 6; https://doi.org/10.3390/astronomy4020006 - 2 Apr 2025
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de Grijs and Bono (ApJS 2020, 246, 3) compiled a list of distances to M87 from the literature published in the last 100 years. They reported the arithmetic mean of the three most stable tracers (Cepheids, tip of the red giant branch, and
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de Grijs and Bono (ApJS 2020, 246, 3) compiled a list of distances to M87 from the literature published in the last 100 years. They reported the arithmetic mean of the three most stable tracers (Cepheids, tip of the red giant branch, and surface brightness fluctuations). The arithmetic mean is one of the measures of central tendency of a distribution; others are the median and mode. The three do not align for asymmetric distributions, which is the case for the distance moduli to M87. I construct a kernel density distribution of the set of and estimate the recommended distance to M87 as its mode, obtaining mag, corresponding to Mpc, which yields uncertainties smaller than those associated with the mean and median.
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Open AccessReview
Solar Particle Acceleration
by
Donald V. Reames
Astronomy 2025, 4(1), 5; https://doi.org/10.3390/astronomy4010005 - 18 Mar 2025
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High-energy particles may be accelerated widely in stellar coronae; probably by the same processes we find in the Sun. Here, we have learned of two physical mechanisms that dominate the acceleration of solar energetic particles (SEPs). The highest energies and intensities are produced
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High-energy particles may be accelerated widely in stellar coronae; probably by the same processes we find in the Sun. Here, we have learned of two physical mechanisms that dominate the acceleration of solar energetic particles (SEPs). The highest energies and intensities are produced in “gradual” events where shock waves are driven from the Sun by fast and wide coronal mass ejections (CMEs). Smaller, but more numerous “impulsive” events with unusual particle compositions are produced during magnetic reconnection in solar jets and flares. Jets provide open magnetic field lines where SEPs can escape. Closed magnetic loops contain this energy to produce bright, hot flares; perhaps even contributing to heating the low corona in profuse nanoflares. Streaming protons amplify Alfvén waves upstream of the shocks. These waves scatter and trap SEPs and, in large events, modify the element abundances and flatten the low-energy spectra upstream. Shocks also re-accelerate the residual ions from earlier impulsive events, when available, that characteristically dominate the energetic heavy-ion abundances. The large CME-driven shock waves develop an extremely wide longitudinal span, filling much of the inner heliosphere with energetic particles.
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Open AccessArticle
Deciphering the Electron Spectral Hardening in AMS-02
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Carmelo Evoli
Astronomy 2025, 4(1), 4; https://doi.org/10.3390/astronomy4010004 - 28 Feb 2025
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We analyze the electron cosmic-ray spectrum from AMS-02, focusing on the spectral hardening around 42 GeV. Our findings confirm that this feature is intrinsic to the primary electron component rather than a byproduct of contamination from primary positron sources. Even under conservative assumptions,
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We analyze the electron cosmic-ray spectrum from AMS-02, focusing on the spectral hardening around 42 GeV. Our findings confirm that this feature is intrinsic to the primary electron component rather than a byproduct of contamination from primary positron sources. Even under conservative assumptions, its significance remains at about , strongly indicating a genuine spectral break. Accordingly, we introduce a new, more realistic parametric fit, which we recommend for the next round of AMS-02 analyses. Once the sources of systematic uncertainties are better constrained, this refined approach can either reinforce or refute our conclusions, providing a clearer understanding of the observed electron spectrum. If confirmed, we propose that this hardening most likely arises from interstellar transport or acceleration effects.
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Open AccessArticle
Line Ratio in the C-like Ion Spectrum O III: Testing Atomic Theory Predictions Through the Observation of Galaxies
by
Julius Richard Dreisbach, Dominik J. Bomans and Elmar Träbert
Astronomy 2025, 4(1), 3; https://doi.org/10.3390/astronomy4010003 - 10 Feb 2025
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The progress made in atomic structure computations has indicated that certain line ratios of forbidden transitions may be slightly different from earlier assumptions. In order to check this theory, we evaluate previous observations of dwarf galaxies by the UVES spectrograph at the VLT
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The progress made in atomic structure computations has indicated that certain line ratios of forbidden transitions may be slightly different from earlier assumptions. In order to check this theory, we evaluate previous observations of dwarf galaxies by the UVES spectrograph at the VLT telescope on ESO Paranal for the line ratios of branched decays in C-like oxygen ions [O III] that are insensitive to the local environment. Our findings show that the observed line ratio for [O III] ( ) aligns with recent theoretical predictions based on more sophisticated models, while it deviates from older computations. Additionally, the analysis of line profiles suggests that, in some cases, the spectral resolution was insufficient to fully resolve dynamic substructures within the galaxies. Our results emphasize the importance of improved data quality and consistency for future studies, especially for future searches of finestructure constant variations at higher redshifts using this method.
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Open AccessArticle
Tracing the Evolution of the Emission Properties of Carbon-Rich AGB, Post-AGB, and PN Sources
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Silvia Tosi and Ester Marini
Astronomy 2025, 4(1), 2; https://doi.org/10.3390/astronomy4010002 - 20 Jan 2025
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Understanding the transition from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase is crucial for advancing our knowledge of galaxy evolution and the chemical enrichment of the universe. In this manuscript, we analyze 137 carbon-rich, evolved low- and intermediate-mass stars
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Understanding the transition from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase is crucial for advancing our knowledge of galaxy evolution and the chemical enrichment of the universe. In this manuscript, we analyze 137 carbon-rich, evolved low- and intermediate-mass stars (LIMSs) from both the Magellanic Clouds (MCs) and the Milky Way (MW). We focus on AGB, post-AGB, and PN sources, tracing the evolution of their emission through spectral energy distribution (SED) modeling. Consistent with previous studies, we observe that more evolved LIMSs exhibit cooler dust temperatures and lower optical depths. Amorphous carbon (amC) is the dominant dust species in all the evolutionary stages examined in this work, while silicon carbide (SiC) accounts for 5–30% of the total dust content. Additionally, we analyze color–color diagrams (CCDs) in the infrared using data from IRAC, WISE, and 2MASS, uncovering significant evolutionary trends in LIMS emission. AGB stars evolve from bluer to redder colors as they produce increasing amounts of dust. Post-AGB and PN sources are clearly differentiated from AGB stars, reflecting shifts in both effective stellar and dust temperatures as the stars transition through these evolutionary phases.
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Open AccessArticle
An Investigation of the Entropy Associated with a Collapsing Molecular Cloud
by
Gemechu Muleta Kumssa
Astronomy 2025, 4(1), 1; https://doi.org/10.3390/astronomy4010001 - 17 Jan 2025
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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
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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.
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Open AccessArticle
Axion Mass and the Ground State of Deconfining SU(2) Yang–Mills Thermodynamics
by
Ralf Hofmann, Janning Meinert and Dmitry Antonov
Astronomy 2024, 3(4), 319-333; https://doi.org/10.3390/astronomy3040020 - 18 Dec 2024
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For the deconfinement phase of an SU(2) Yang–Mills theory, we compute the axion mass by appealing to the Veneziano–Witten formula. The topological susceptibility arises (i) from a precisely computable thermal ground-state contribution due to a center of a relevant (anti)caloron,
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For the deconfinement phase of an SU(2) Yang–Mills theory, we compute the axion mass by appealing to the Veneziano–Witten formula. The topological susceptibility 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 , contribution (ii) is negative, as demanded by reflection positivity, but negligible compared to contribution (i). As a consequence, practically from the critical temperature onward, a real-valued axion mass emerges when the Peccei–Quinn scale is assumed to be the Planck mass , 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 , we investigate the cosmological conditions for their global Bose condensation as the very early universe cooled to temperatures of the order of eV.
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Open AccessArticle
Towards the Particle Spectrum, Tickled by a Distant Massive Object
by
Mehdi Dehghani, Salman A. Nejad and Maryam Mardaani
Astronomy 2024, 3(4), 304-318; https://doi.org/10.3390/astronomy3040019 (registering DOI) - 12 Dec 2024
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To investigate the gravitational effects of massive objects on a typical observer, we studied the dynamics of a test particle following geodesics. We constructed the framework using the canonical phase space formalism and the corresponding Hamiltonian. We focused on
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To investigate the gravitational effects of massive objects on a typical observer, we studied the dynamics of a test particle following geodesics. We constructed the 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.
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Open AccessArticle
The Complex Structure of the Abell 548–Abell 3367 Region
by
Mark J. Henriksen and Layla Ahmed
Astronomy 2024, 3(4), 289-303; https://doi.org/10.3390/astronomy3040018 - 18 Nov 2024
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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
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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.
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Open AccessArticle
Separating the Spectral Counterparts in NGC 1275/Perseus Cluster in X-Rays
by
Elena Fedorova, Lidiia Zadorozhna, Anatolii Tugay, Nadiia Pulatova, Alexander Ganz and Olexandr Gugnin
Astronomy 2024, 3(4), 275-288; https://doi.org/10.3390/astronomy3040017 - 18 Oct 2024
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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
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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.
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Open AccessArticle
An Event Horizon ‘Firewall’ Undergoing Cosmological Expansion
by
Richard N. Henriksen and A. Gordon Emslie
Astronomy 2024, 3(3), 255-274; https://doi.org/10.3390/astronomy3030016 - 23 Sep 2024
Abstract
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
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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.
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(This article belongs to the Special Issue Current Trends in Cosmology)
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