Journal Description
Galaxies
Galaxies
is an international, peer-reviewed, open access journal on astronomy, astrophysics, and cosmology published bimonthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, ESCI (Web of Science), Astrophysics Data System, INSPIRE, Inspec, and other databases.
- Journal Rank: JCR - Q2 (Astronomy and Astrophysics) / CiteScore - Q2 (Astronomy and Astrophysics)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 23.4 days after submission; acceptance to publication is undertaken in 4.8 days (median values for papers published in this journal in the first half of 2025).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Impact Factor:
3.8 (2024);
5-Year Impact Factor:
3.1 (2024)
Latest Articles
Molecules and Chemistry in Red Supergiants
Galaxies 2025, 13(4), 82; https://doi.org/10.3390/galaxies13040082 - 21 Jul 2025
Abstract
The envelopes of Red Supergiants (RSGs) have a unique chemical environment not seen in other types of stars. They foster an oxygen-rich synthesis but are tempered by sporadic and chaotic mass loss, which distorts the envelope and creates complex outflow sub-structures consisting of
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The envelopes of Red Supergiants (RSGs) have a unique chemical environment not seen in other types of stars. They foster an oxygen-rich synthesis but are tempered by sporadic and chaotic mass loss, which distorts the envelope and creates complex outflow sub-structures consisting of knots, clumps, and arcs. Near the stellar photosphere, molecules and grains form under approximate LTE conditions, as predicted by chemical models. However, the complicated outflows appear to have distinct chemistries generated by shocks and dust destruction. Various RSG envelopes have been probed for their molecular content, mostly by radio and millimeter observations; however, VY Canis Majoris (VY CMa) and NML Cygni (NML Cyg) display the highest chemical complexity, and also the most complicated envelope structure. Thus far, over 29 different molecules have been identified in the envelopes of RSGs. Some molecules are common for circumstellar gas, including CO, SiO, HCN and H2O, which have abundances of ∼10−6–10−4, relative to H2. More exotic oxides have additionally been discovered, such as AlO, AlOH, PO, TiO2, and VO, with abundances of ∼10−9–10−7. RSG shells support intricate maser emission in OH, H2O and SiO, as well. Studies of isotope ratios in molecules suggest dredge-up at least into the H-burning shell, but further exploration is needed.
Full article
(This article belongs to the Special Issue The Red Supergiants: Crucial Signposts for the Fate of Massive Stars)
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Open AccessReview
Stellar Evolution Through the Red Supergiant Phase
by
Sylvia Ekström and Cyril Georgy
Galaxies 2025, 13(4), 81; https://doi.org/10.3390/galaxies13040081 - 17 Jul 2025
Abstract
Massive stars less massive than ∼30 evolve into a red supergiant after the main sequence. Given a standard IMF, this means about 80% of all single massive stars will experience this phase. RSGs are dominated by convection, with a radius that
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Massive stars less massive than ∼30 evolve into a red supergiant after the main sequence. Given a standard IMF, this means about 80% of all single massive stars will experience this phase. RSGs are dominated by convection, with a radius that may extend up to thousands of solar radii. Their low temperature and gravity make them prone to losing large amounts of mass, either through pulsationally driven wind or through mass-loss outburst. RSGs are the progenitors of the most common core-collapse supernovae, type II. In the present review, we give an overview of our theoretical understanding about this spectacular phase of massive star evolution.
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(This article belongs to the Special Issue The Red Supergiants: Crucial Signposts for the Fate of Massive Stars)
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Open AccessArticle
Doppler Tomography of the Be Star HD 698
by
Ilfa A. Gabitova, Sergey V. Zharikov, Anatoly S. Miroshnichenko, Alex Carciofi, Azamat A. Khokhlov, Aldiyar Agishev and Peter Prendergast
Galaxies 2025, 13(4), 80; https://doi.org/10.3390/galaxies13040080 - 16 Jul 2025
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We present a Doppler tomography study of the Be star HD 698, recently resolved via interferometry as a post-mass-transfer binary system consisting of a Be star and a stripped, pre-subdwarf companion. Based on 76 high-resolution optical spectra obtained between 2014 and 2023, we
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We present a Doppler tomography study of the Be star HD 698, recently resolved via interferometry as a post-mass-transfer binary system consisting of a Be star and a stripped, pre-subdwarf companion. Based on 76 high-resolution optical spectra obtained between 2014 and 2023, we analyze the H and H emission lines and apply Doppler tomography to map the structure of the circumstellar disk. The H line reveals an asymmetric, multi-component velocity distribution, with an emission feature closely following the orbital motion of the companion. V/R variations in both H and H lines are phase-locked with the companion’s orbital motion, indicating a tidally induced disk asymmetry. We discuss possible origins of the companion-centered H emission, including a circumsecondary disk, a transient mass-transfer stream, and stellar wind.
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Open AccessArticle
1PN Effective Binary Lagrangian for the Gravity–Kalb–Ramond Sector in the Conservative Regime
by
Vegard Undheim, Eirik Eik Svanes and Alex B. Nielsen
Galaxies 2025, 13(4), 79; https://doi.org/10.3390/galaxies13040079 - 8 Jul 2025
Abstract
Within the framework of string theory, a number of new fields can arise that correct the Einstein–Hilbert action, including the Kalb–Ramond two-form field. In this work, we derive explicitly first-order relativistic corrections to conservative dynamics in the presence of a Kalb–Ramond field using
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Within the framework of string theory, a number of new fields can arise that correct the Einstein–Hilbert action, including the Kalb–Ramond two-form field. In this work, we derive explicitly first-order relativistic corrections to conservative dynamics in the presence of a Kalb–Ramond field using the effective field theory approach. The resulting additional terms in the Lagrangian governing conservative binary dynamics are presented explicitly.
Full article
(This article belongs to the Special Issue Cosmology and the Quantum Vacuum—2nd Edition)
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Open AccessArticle
Unveiling the Evolution of MWC 728: Non-Conservative Mass Transfer in an FS CMa Binary
by
Nadezhda L. Vaidman, Serik A. Khokhlov and Aldiyar T. Agishev
Galaxies 2025, 13(4), 78; https://doi.org/10.3390/galaxies13040078 - 7 Jul 2025
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We combine corrected Gaia DR3 astrometry with non-conservative MESA modelling to retrace the evolution of the FS-CMa binary MWC 728. The revised parallax sets the distance at kpc, leading—after Monte-Carlo error propagation—to luminosities of
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We combine corrected Gaia DR3 astrometry with non-conservative MESA modelling to retrace the evolution of the FS-CMa binary MWC 728. The revised parallax sets the distance at kpc, leading—after Monte-Carlo error propagation—to luminosities of and , corresponding to the accretor and donor, respectively. A fiducial binary track that starts with , , and d reproduces the observations provided the Roche-lobe overflow, which is moderately non-conservative: only of the transferred mass is retained by the accretor, while the remainder leaves the system via (i) a fast isotropic wind from the donor ( ), (ii) isotropic re-emission near the accretor ( ), and (iii) outflow into a circumbinary torus ( , lever arm ). These channels remove sufficient angular momentum to expand the orbit to the observed d while sustaining the dusty circumbinary outflow. At Myr, the model matches every current observable: , , mass ratio , and an ongoing transfer rate of . MWC 728 thus serves as a benchmark intermediate-mass binary for testing how non-conservative outflows regulate angular-momentum loss and orbital growth.
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Open AccessReview
Mass Loss in Be Stars: News from Two Fronts
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Alex C. Carciofi, Guilherme P. P. Bolzan, Pâmela R. Querido, Amanda C. Rubio, Jonathan Labadie-Bartz, Tajan H. de Amorim, Ariane C. Fonseca Silva and Vittória L. Schiavolim
Galaxies 2025, 13(4), 77; https://doi.org/10.3390/galaxies13040077 - 7 Jul 2025
Abstract
Be stars are characterized by the presence of a circumstellar Keplerian disk formed from material ejected from the rapidly rotating stellar surface. This article presents recent observational and theoretical progress on two central aspects of this phenomenon: the mechanisms driving mass loss, and
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Be stars are characterized by the presence of a circumstellar Keplerian disk formed from material ejected from the rapidly rotating stellar surface. This article presents recent observational and theoretical progress on two central aspects of this phenomenon: the mechanisms driving mass loss, and the fate of the ejected material. Using simultaneous TESS photometry and ground-based spectroscopy, we examine the short-term variability associated with discrete mass ejection events, or “flickers”, and review strong evidence linking them to pulsational activity near the stellar surface. Complementary 3D hydrodynamic simulations reproduce key observational signatures and establish that disk formation requires compact and asymmetric ejection sites with sufficient angular momentum to overcome re-accretion. In systems with binary companions, new high-resolution simulations resolve the outer disk for the first time and identify five dynamically distinct regions, including a circumsecondary disk and a circumbinary spiral outflow. Together, these results provide a coherent framework that traces the full life cycle of disk material from pulsation-driven ejection near the stellar surface to its final destination, whether re-accreted by the companion or lost from the system entirely.
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(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)
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Quantifying the Unwinding Due to Ram Pressure Stripping in Simulated Galaxies
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Rubens E. G. Machado, Caroline F. O. Grinberg and Elvis A. Mello-Terencio
Galaxies 2025, 13(4), 76; https://doi.org/10.3390/galaxies13040076 - 7 Jul 2025
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Galaxies moving through the gas of the intracluster medium (ICM) experience ram pressure stripping, which can leave behind a gas tail. When a disk galaxy receives the wind edge-on, however, the characteristic signature is not a typical jellyfish tail, but rather an unwinding
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Galaxies moving through the gas of the intracluster medium (ICM) experience ram pressure stripping, which can leave behind a gas tail. When a disk galaxy receives the wind edge-on, however, the characteristic signature is not a typical jellyfish tail, but rather an unwinding of the spiral arms. We aim to quantify such asymmetries both in the gas and in the stellar component of a simulated galaxy. To this end, we simulate a gas-rich star-forming spiral galaxy moving through a self-consistent ICM gas. The amplitude and location of the asymmetries were measured via Fourier decomposition. We found that the asymmetry is much more evident in the gas component, but it is also measurable in the stars. The amplitude tends to increase with time and the asymmetry radius migrates inwards. We found that, when considering the gas, the spiral arms extend much further and are more unwound than the corresponding stellar arms. Characterizing the unwinding via simulations should help inform the observational criteria used to classify ram pressure stripped galaxies, as opposed to asymmetries induced by other mechanisms.
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Open AccessArticle
The I-Love Universal Relation for Polytropic Stars Under Newtonian Gravity
by
Rui Xu, Alejandro Torres-Orjuela and Pau Amaro Seoane
Galaxies 2025, 13(4), 75; https://doi.org/10.3390/galaxies13040075 - 2 Jul 2025
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The moment of inertia and tidal deformability of idealized stars with polytropic equations of state (EOSs) are numerically calculated under both Newtonian gravity and general relativity (GR). The results explicitly confirm that the relation between the moment of inertia and tidal deformability, parameterized
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The moment of inertia and tidal deformability of idealized stars with polytropic equations of state (EOSs) are numerically calculated under both Newtonian gravity and general relativity (GR). The results explicitly confirm that the relation between the moment of inertia and tidal deformability, parameterized by the star’s mass, exhibits variations up to and for different polytropic indices in Newtonian gravity and GR, respectively. This indicates a more robust I-Love universal relation in the Newtonian framework. The theoretically derived I-Love universal relation for polytropic stars is subsequently tested against observational data for the moment of inertia and tidal deformability of the eight planets and some moons in our solar system. The analysis reveals that the theoretical I-Love universal relation aligns well with the observational data, suggesting that it can serve as an empirical relation. Consequently, it enables the estimation of either the moment of inertia or the tidal deformability of an exoplanet if one of these quantities, along with the mass of the exoplanet, is known.
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Open AccessArticle
The BSN Application-I: Photometric Light Curve Solutions of Contact Binary Systems
by
Ehsan Paki, Atila Poro and Minoo Dokht Moosavi Rowzati
Galaxies 2025, 13(4), 74; https://doi.org/10.3390/galaxies13040074 - 30 Jun 2025
Abstract
Light curve analysis of W UMa-type contact binary systems using MCMC or MC methods can be time-consuming, primarily because the repeated generation of synthetic light curves tends to be relatively slow during the fitting process. Although various approaches have been proposed to address
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Light curve analysis of W UMa-type contact binary systems using MCMC or MC methods can be time-consuming, primarily because the repeated generation of synthetic light curves tends to be relatively slow during the fitting process. Although various approaches have been proposed to address this issue, their implementation is often challenging due to complexity or uncertain performance. In this study, we introduce the BSN application, whose name is taken from the BSN project. The application is designed for analyzing contact binary system light curves, supporting photometric data, and employing an MCMC algorithm for efficient parameter estimation. The BSN application generates synthetic light curves more than 40 times faster than PHOEBE during the MCMC fitting process. The BSN application enhances light curve analysis with an expanded feature set and a more intuitive interface while maintaining compliance with established scientific standards. In addition, we present the first light curve analyses of four contact binary systems based on the TESS data, utilizing the BSN application version 1.0. We also conducted a light curve analysis using the PHOEBE Python code and compared the resulting outputs. Two of the target systems exhibited asymmetries in the maxima of their light curves, which were appropriately modeled by introducing a cold starspot on one of the components. The estimated mass ratios of these total-eclipse systems place them within the category of low mass ratio contact binary stars. The estimation of the absolute parameters for the selected systems was carried out using the empirical relationship. Based on the effective temperatures and masses of the components, three of the target systems were classified as A-subtype, while TIC 434222993 was identified as a W-subtype system.
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(This article belongs to the Special Issue Study on Contact Binary Stars)
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ALMA Observations of G333.6-0.2: Molecular and Ionized Gas Environment
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Aruzhan Omar, Aidana Abdirakhman, Nazgul Alimgazinova, Meiramgul Kyzgarina, Aisha Naurzbayeva, Zhomartkali Islyam, Kunduz Turekhanova, Aizat Demessinova and Arailym Manapbayeva
Galaxies 2025, 13(4), 73; https://doi.org/10.3390/galaxies13040073 - 27 Jun 2025
Abstract
We present high-angular resolution observations, conducted with the Atacama Large Millimeter/Submillimeter Array (ALMA) in Band 6, of high-excitation molecular lines of , CH3OH, and the H29 radio recombination line, towards the G333.6-0.2 ultracompact (UC) H ii region.
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We present high-angular resolution observations, conducted with the Atacama Large Millimeter/Submillimeter Array (ALMA) in Band 6, of high-excitation molecular lines of , CH3OH, and the H29 radio recombination line, towards the G333.6-0.2 ultracompact (UC) H ii region. Our observations reveal three hot molecular cores: A, B, and C, where emission is detected in ten components of the rotational ladder of and in the CH3OH transition. Rotational diagram analysis of reveals excitation temperatures ranging from 380 to 430 K. First-order moment maps of and CH3OH reveal distinct velocity gradients in all cores, suggesting rotating structures, with core A also showing evidence of expansion motions. The H29 recombination line shows a linewidth of km s−1, dominated by dynamical and thermal broadening, indicative of large-scale motions in ionized gas. Analysis of the ionized gas properties yields an electron density of cm−3, an emission measure of pc cm−6, and a Lyman continuum photon flux consistent with an O5–O6 V (Zero-Age Main Sequence; ZAMS) star. Our results suggest that G333.6-0.2 is in an intermediate evolutionary stage between hypercompact (HC) and ultracompact (UC) H ii regions, hosting active high-mass star formation with rotating hot cores and ionized gas dynamics.
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(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)
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Open AccessReview
Red Supergiant Mass Loss and Mass-Loss Rates
by
Jacco Th. van Loon
Galaxies 2025, 13(4), 72; https://doi.org/10.3390/galaxies13040072 - 20 Jun 2025
Abstract
This review discusses the causes, nature, importance and observational evidence of mass loss by red supergiants. It arrives at the perception that mass loss finds its origin in the gravity which makes the star a star in the first place, and is a
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This review discusses the causes, nature, importance and observational evidence of mass loss by red supergiants. It arrives at the perception that mass loss finds its origin in the gravity which makes the star a star in the first place, and is a mechanism for the star to equilibrate. This is corroborated by a careful examination of various popular historical and recent empirical mass-loss rate prescriptions and theoretical works, and which provides no evidence for an explicit dependence of red supergiant mass loss on metallicity though dust-associated mass loss becomes less prevalent at lower metallicity. It also identifies a common problem in methods that use tracers of mass loss, which do not correct for varying scaling factors (often because there is no information available on which to base such correction) and as a result tend to underestimate mass-loss rates at the lower end. Conversely, dense, extended chromospheres in themselves do not translate into high mass-loss rates, and the significance of stochastic mass loss can be overstated. On a population scale, on the other hand, binary interaction acts as a stochastic agent of mass loss of great import. In all, evidence is overwhelming that points at red supergiants at the lower mass end losing mass at insufficient rates to shed their mantles before core collapse, but massive (at birth) red supergiants to be prone to intense, dusty mass loss which sees them become hotter stars before meeting their fate. This is consistent with the identified progenitors of hydrogen-rich supernovae. Supernova evolution holds great promise to probe the mass loss but we caution against confusing atmospheres with winds. Finally, promising avenues are looked into, which could forge step-change progress in what has been a long and arduous search for the holy grail of red supergiant mass loss. We may yet find it!
Full article
(This article belongs to the Special Issue The Red Supergiants: Crucial Signposts for the Fate of Massive Stars)
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CMB Multipole Expansion in a Frame Dragging-Sustained Milky Way
by
Federico Re, Marco Galoppo and Massimo Dotti
Galaxies 2025, 13(3), 71; https://doi.org/10.3390/galaxies13030071 - 13 Jun 2025
Abstract
We study the impact on the cosmic microwave background (CMB) landscape of peculiar rotational general relativistic effects. These effects, on galactic scales, do not possess a Newtonian analogue, and therefore could a priori impact CMB analysis. We find that the velocity inferred from
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We study the impact on the cosmic microwave background (CMB) landscape of peculiar rotational general relativistic effects. These effects, on galactic scales, do not possess a Newtonian analogue, and therefore could a priori impact CMB analysis. We find that the velocity inferred from the CMB dipole, under the kinematic interpretation, coincides with that measured by a stationary observer within the Milky Way and not with the one measured by the zero angular momentum observer. We show that the galaxy peculiar frame-dragging effects do not impact the standard CMB analysis, as these modify the multipole coefficients only at higher orders with respect to the dominant terms. Moreover, we prove that no general relativistic framework at the galactic scale patched within the standard cosmological model can account for the current tension on the CMB quadrupole amplitude.
Full article
(This article belongs to the Special Issue Cosmology and the Quantum Vacuum—2nd Edition)
Open AccessCommunication
The Enigmatic, Highly Variable, High-Mass Young Stellar Object Mol 12: A New Extreme Herbig Be (Proto)star
by
Mauricio Tapia, Paolo Persi, Jesús Hernández and Nuria Calvet
Galaxies 2025, 13(3), 70; https://doi.org/10.3390/galaxies13030070 - 13 Jun 2025
Abstract
We report new medium-resolution spectroscopy covering the wavelength range from 0.6 to 2.4 m, as well as multi-epoch, multi-wavelength photometry, of the Class I high-mass embedded young stellar object Mol 12 (IRAS 05373+2349). It is embedded ( )
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We report new medium-resolution spectroscopy covering the wavelength range from 0.6 to 2.4 m, as well as multi-epoch, multi-wavelength photometry, of the Class I high-mass embedded young stellar object Mol 12 (IRAS 05373+2349). It is embedded ( ) in the centre of a dense core at a distance of 1.59 kpc from the Sun and has a total luminosity of . The spectra show a large number of permitted atomic emission lines, mostly for Fe, H, C, N, and Ca, that originate in the inner zones of a very active protoplanetary disc and no photospheric absorption lines. Conspicuously, the He I line at 1.0830 m displays a complex P-Cygni profile. Also, the first overtone CO emission band-heads at 2.3 m are seen in emission. From the strengths of the principal emission lines, we determined the accretion rate and luminosity to be y−1 and , respectively. Decade-long light curves show a series of irregular brightness dips of more than four magnitudes in r, becoming shallower as the wavelength increases and disappearing at m. The colour–magnitude diagrams suggest the occurrence of a series of eclipses caused by the passage of small dust cloudlets in front of the star, producing more than 10 magnitudes of extra extinction.
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(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)
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Numerical Solutions and Stability Analysis of White Dwarfs with a Generalized Anisotropic Factor
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Ayazhan Orazymbet, Aray Muratkhan, Daniya Utepova, Nurzada Beissen, Gulzada Baimbetova and Saken Toktarbay
Galaxies 2025, 13(3), 69; https://doi.org/10.3390/galaxies13030069 - 12 Jun 2025
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This study examines the equilibrium structure and stability of white dwarfs, incorporating both isotropic and anisotropic pressure distributions. The Tolman–Oppenheimer–Volkoff (TOV) equation is numerically solved using the Chandrasekhar equation of state (EoS) to analyze the effects of pressure anisotropy. A general anisotropy function
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This study examines the equilibrium structure and stability of white dwarfs, incorporating both isotropic and anisotropic pressure distributions. The Tolman–Oppenheimer–Volkoff (TOV) equation is numerically solved using the Chandrasekhar equation of state (EoS) to analyze the effects of pressure anisotropy. A general anisotropy function is introduced to close and solve the system of differential equations. The results indicate that anisotropy remains negligible at the center and increases toward the stellar surface. Stability is assessed using the speed of sound criterion, , and the Buchdahl bound, , confirming that white dwarfs remain within stability limits. We performed a sensitivity analysis to examine how variations in the anisotropy parameter and central density affect the mass, radius, and compactness of white dwarfs. Additionally, we calculated the gravitational redshift at the stellar surface and found that it varies with anisotropy, ranging from in isotropic cases to in highly anisotropic models. These results link anisotropy to potentially observable features. The findings suggest that while anisotropy does not significantly affect the overall equilibrium structure, it may play a role in astrophysical scenarios involving strong magnetic fields, rotational deformations, or accretion processes in binary systems.
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Open AccessArticle
Post-AGB Binaries as Interacting Systems
by
Hans Van Winckel
Galaxies 2025, 13(3), 68; https://doi.org/10.3390/galaxies13030068 - 12 Jun 2025
Abstract
We present recent progress in our understanding of the physical interaction mechanisms at work in evolved binaries of low-to-intermediate initial mass, which are surrounded by a stable disc of gas and dust. These systems are known as post-asymptotic giant-branch (post-AGB) binaries, but recently,
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We present recent progress in our understanding of the physical interaction mechanisms at work in evolved binaries of low-to-intermediate initial mass, which are surrounded by a stable disc of gas and dust. These systems are known as post-asymptotic giant-branch (post-AGB) binaries, but recently, it has been shown that some systems are too low in luminosity and should be considered as post-red-giant branch (post-RGB) instead. While the systems are currently well within their Roche lobe, they still show signs of active ongoing interaction between the different building blocks. We end this contribution with some future research plans.
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(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)
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Searching for New Objects with the B[e] Phenomenon
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Aisha Zh. Naurzbayeva, Nazgul Sh. Alimgazinova, Anatoly S. Miroshnichenko, Corinne Rossi, Inna V. Reva, Raushan I. Kokumbayeva, Chingis T. Omarov, Sergei V. Zharikov, Nadine Manset, Ashish Raj, Arti Joshi, Richard J. Rudy, Richard C. Puetter, Raleigh B. Perry and Kunduz M. Turekhanova
Galaxies 2025, 13(3), 67; https://doi.org/10.3390/galaxies13030067 - 11 Jun 2025
Abstract
Objects with the B[e] phenomenon, whose defining features are the presence of forbidden emission lines and infrared excess coming from circumstellar dust, represent a broad range of evolutionary stages from pre-main-sequence to planetary nebulae. They are important for understanding mechanisms of the circumstellar
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Objects with the B[e] phenomenon, whose defining features are the presence of forbidden emission lines and infrared excess coming from circumstellar dust, represent a broad range of evolutionary stages from pre-main-sequence to planetary nebulae. They are important for understanding mechanisms of the circumstellar matter formation and evolution. However, it is not easy to discover them, especially among faint stars, as forbidden emission lines are usually weak and hardly noticeable in low-resolution spectra. We developed photometric criteria to search for candidate objects with this phenomenon based on a combination of optical and near-infrared color indices and found nearly 40 objects that satisfy these criteria. Spectroscopy of the candidates allows us to make more confident conclusions on their classification. We present the results of our photometric and spectroscopic observations of six objects, which are part of a large list of ∼40 objects that satisfy our photometric selection criteria for candidate objects with the B[e] phenomenon. Forbidden lines of neutral oxygen were clearly detected in the optical spectrum of one object (VES 683) and suspected in three others. One object, AS 415, is most likely a binary system with components that exhibit partial eclipses but without the B[e] phenomenon, while IRAS 20402 + 4638 may be a luminous member of the FS CMa objects group.
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(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)
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Open AccessReview
Red Supergiants in the Milky Way and Nearby Galaxies
by
Alceste Z. Bonanos
Galaxies 2025, 13(3), 66; https://doi.org/10.3390/galaxies13030066 - 5 Jun 2025
Abstract
Identifications of red supergiants (RSGs) in the Milky Way and nearby galaxies have experienced an exponential increase in recent years, driven by advancements in selection techniques, the continued expansion of archival datasets, and a steady increase in spectroscopic data. This review describes the
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Identifications of red supergiants (RSGs) in the Milky Way and nearby galaxies have experienced an exponential increase in recent years, driven by advancements in selection techniques, the continued expansion of archival datasets, and a steady increase in spectroscopic data. This review describes the advances in methodologies and selection criteria for identifying RSGs and presents the current census of these stars in our own Galaxy and nearby galaxies. It also describes the insights gained from resolving nearby RSGs and their complex circumstellar material in the Milky Way and from the growing samples of RSGs being discovered in the Local Group and beyond. These advances impact the Humphreys–Davidson limit in the cool part of the Hertzsprung–Russell diagram. Furthermore, they provide insight into extreme RSGs and the role of photometric variability and, in particular, of the newly discovered phenomenon of dimming events. Recent observations have enabled the determination of the binarity fraction among RSGs, offering new constraints to stellar evolution. Looking ahead, the synergy between large-scale surveys, high-resolution observations, and emerging machine-learning tools promises to further transform our understanding of the final evolutionary stages of massive stars in the coming decade.
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(This article belongs to the Special Issue The Red Supergiants: Crucial Signposts for the Fate of Massive Stars)
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Open AccessReview
Estimating Hubble Constant with Gravitational Observations: A Concise Review
by
Rosa Poggiani
Galaxies 2025, 13(3), 65; https://doi.org/10.3390/galaxies13030065 - 4 Jun 2025
Abstract
The Hubble constant is of paramount importance in astrophysics and cosmology. A large number of methods have been developed with different electromagnetic probes to estimate its value. The most recent results show a tension between values obtained from Cosmic Microwave Background observations and
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The Hubble constant is of paramount importance in astrophysics and cosmology. A large number of methods have been developed with different electromagnetic probes to estimate its value. The most recent results show a tension between values obtained from Cosmic Microwave Background observations and supernovae. The simultaneous detection of gravitational waves and electromagnetic radiation from GW170817 provided a direct estimation of the Hubble constant that did not depend on the astronomical distance ladder. This concise review will present the methods to estimate the Hubble constant with the gravitational observations of compact binary mergers, discussing both bright and dark sirens and reporting the state of the art of the results.
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(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)
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Open AccessReview
Dust at the Cosmic Dawn
by
Yuri A. Shchekinov and Biman B. Nath
Galaxies 2025, 13(3), 64; https://doi.org/10.3390/galaxies13030064 - 23 May 2025
Abstract
Observations provided by the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) have revealed a surprising abundance of galaxies at the “cosmic dawn” epoch, . Some of them are found even in a more distant universe at z
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Observations provided by the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) have revealed a surprising abundance of galaxies at the “cosmic dawn” epoch, . Some of them are found even in a more distant universe at z ≃ 14–16. Most of these galaxies appear to be intriguing: they are found to be either super-bright in the rest-frame ultraviolet (UV) band or super-dusty with a heavily reddened stellar population. The transition from the super-bright and super-dusty regimes seems to occur in the redshift range from z∼10.5 to z∼9.5 within a time range of ∼50 Myr. If confirmed, then the origin of this transition is far from being clear. In the review, we discuss possible mechanisms that can make galaxies free of dust and also explain the origin of apparently excessive dust in galaxies at intermediate and lower redshifts .
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(This article belongs to the Special Issue The Observation and Detection of Dusty Star-Forming Galaxies)
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Open AccessArticle
A Spectroscopic and Photometric Study of MWC 342 and Its B[e] Phenomenon over the Last 40 Years
by
Aigerim Zh. Akniyazova, Anatoly S. Miroshnichenko, Sergey V. Zharikov, Hans Van Winckel, Nadine Manset, Ashish Raj, Stephen Drew Chojnowski, Serik A. Khokhlov, Inna V. Reva, Raushan I. Kokumbaeva, Chingis T. Omarov, Konstantin N. Grankin, Aldiyar T. Agishev and Nadezhda L. Vaidman
Galaxies 2025, 13(3), 63; https://doi.org/10.3390/galaxies13030063 - 20 May 2025
Abstract
MWC 342 (V1972 Cyg) was discovered nearly 90 years ago as an early-type emission-line star. It was among the first hot stars whose strong infrared excess was detected in the early 1970s. Several mostly short-term photometric and spectroscopic studies resulted in contradictory conclusions
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MWC 342 (V1972 Cyg) was discovered nearly 90 years ago as an early-type emission-line star. It was among the first hot stars whose strong infrared excess was detected in the early 1970s. Several mostly short-term photometric and spectroscopic studies resulted in contradictory conclusions about the nature and evolutionary status of MWC 342. It has been classified as a pre-main-sequence Herbig Be star, an evolved suspected binary system, and a long-period variable star. Suggestions on the nature of the secondary component to this B0/B1 primary included a cool M-type giant and an X-ray source. We collected medium- and high-resolution optical spectra of MWC 342 taken in 1994–2024 as well as optical photometric data taken in 1986–2024. Analysis of these data shows strong variations in the object’s brightness and spectral line properties at various time scales, but no strictly periodic phenomena have been found. Inparticular, such a long-term dataset allowed us to reveal the optical brightness variations over a nearly 20-year-long quasi-period, as well as their anti-correlation with the H emission-line strength. Also, we did not confirm the presence of He ii emission lines and absorption lines of the star’s atmosphere that were suspected in previously published studies.
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(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)
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