Galaxies

17 pages, 16241 KB

Open AccessArticle

Morphokinematic Structure of the Planetary Nebula NGC 6563

by Zahra Al, Federico Soto-Badilla, Yüksel Karataş, Gerardo Ramos-Larios and Roberto Vázquez

Galaxies 2026, 14(3), 60; https://doi.org/10.3390/galaxies14030060 - 15 Jun 2026

We present a morphokinematic analysis based on high-resolution long-slit echelle spectroscopy of the [N ii]

λ 6583

line and narrowband imaging. Position–velocity diagrams reveal asymmetric expansion and localized kinematic features. We derive a systemic velocity of [...] Read more.

We present a morphokinematic analysis based on high-resolution long-slit echelle spectroscopy of the [N ii]

λ 6583

line and narrowband imaging. Position–velocity diagrams reveal asymmetric expansion and localized kinematic features. We derive a systemic velocity of

V_{sys}^{LSR} = - 25 \pm 1

km s⁻¹ (

V_{sys}^{HEL} = - 34 \pm 1

km s⁻¹) and a main shell expansion velocity of

V_{\exp} = 22 \pm 1

km s⁻¹. Three-dimensional modeling indicates an ellipsoidal main body surrounded by a thin shell, two ear-like protrusions, and additional small-scale structures. The corresponding kinematic ages are

3600 \pm 700

yr for the ellipsoid and ring, and

7500 \pm 1000

yr and

8800 \pm 1500

yr for the two opposite ear-like protrusions, respectively, indicating that these outer structures predate the main nebular envelope. The kinematic asymmetry and enhanced emission regions suggest evolution within a non-uniform ambient medium. At the same time, the presence of collimated ear-like structures is consistent with shaping influenced by binary interaction, where earlier outflows preceded the ejection of the dense shell. NGC 6563 therefore appears to be a dynamically evolved system shaped by the combined effects of episodic mass ejection and environmental interaction. Full article

(This article belongs to the Special Issue Origins and Models of Planetary Nebulae, 2nd Edition)

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26 pages, 24396 KB

Open AccessReview

Direct Experiments of Neutron Capture on Stable and Unstable Isotopes for Stellar Nucleosynthesis Studies

by Jorge Lerendegui-Marco, Javier Balibrea-Correa, Victor Babiano-Suarez, César Domingo-Pardo, Gabriel de la Fuente-Rosales, Bernardo Gameiro, Ion Ladarescu, Ariel Tarifeño-Saldivia, Pablo Torres-Sánchez, Oliver Aberle, Victor Alcayne, Simone Amaducci, Michael Bacak, Jesús Bartolomé, Aparna Basavaraja-Allannavar, Ana-Paula Bernardes, Eric Berthoumieux, Roland Beyer, Matthew Birch, Selin Birincioglu, Marian Boromiza, Damir Bosnar, Benedetta Brusasco, Manuel Caamaño, Aline Cahuzac, Francisco Calviño, Marco Calviani, Daniel Cano-Ott, Adrià Casanovas, Donato Castelluccio, Francesco Cerutti, Gabriele Cescutti, Enrico Chiaveri, Gerardo Claps, Paolo Colombetti, Nicola Colonna, Patrizio Console Camprini, Guillem Cortés, Miguel Cortés-Giraldo, Luigi Cosentino, Sergio Cristallo, Angelica D’Ottavi, Maria Diakaki, Mario Di Castro, Augusto Di Chicco, Mirco Dietz, Emmeric Dupont, Ignacio Durán, Zinovia Eleme, Sylvain Fargier, Martin Farkas, Beatriz Fernández-Domínguez, Paolo Finocchiaro, Will Flanagan, Varvara Foteinou, Valter Furman, Aman Gandhi, Francisco García-Infantes, Aleksandra Gawlik-Ramięga, Gianpiero Gervino, Simone Gilardoni, Enrique González-Romero, Styliani Goula, Erich Griesmayer, Carlos Guerrero, Frank Gunsing, Carlo Gustavino, Jan Heyse, William Hillman, Elizabeth Jacoby, David Jenkins, Erwin Jericha, Arnd Junghans, Ulli Köster, Yacine Kadi, Nasser Kalantar-Nayestanaki, Kalliopi Kaperoni, Myroslav Kavatsyuk, Michael Kokkoris, Sotirios Kopanos, Yury Kopatch, Milan Krtička, Nikolaos Kyritsis, Claudia Lederer-Woods, Giuseppe Lorusso, Alice Manna, Trinitario Martínez, Marco Martínez-Cañada, Alessandro Masi, Cristian Massimi, Pierfrancesco Mastinu, Mario Mastromarco, Emilio-Andrea Maugeri, Annamaria Mazzone, Emilio Mendoza, Alberto Mengoni, Veatriki Michalopoulou, Paolo Milazzo, Jacob Moldenhauer, Riccardo Mucciola, Elizabeth Musacchio González, Agatino Musumarra, Alexandru Negret, Emmanuel Odusina, Dimitrios Papanikolaou, Carlos Paradela, Albert Parmenter, Nikolas Patronis, José Antonio Pavón, Maria Pellegriti, Pablo Pérez-Maroto, Alberto Pérez de Rada Fiol, Giulio Perfetto, Jarosław Perkowski, Cristina Petrone, Nicholas Pieretti, Luciano Piersanti, Elisa Pirovano, Ignacio Porras, Javier Praena, José-Manuel Quesada, René Reifarth, Alejandro Reina, Dimitri Rochman, Yuriy Romanets, Annie Rooney, Gerard Rovira, Carlo Rubbia, Adrián Sánchez-Caballero, Nicolás Sánchez-Vázquez, Rudra N. Sahoo, Daniele Scarpa, Gavin Smith, Nikolay Sosnin, Michele Spelta, Krzysztof Stasiak, Giuseppe Tagliente, Antonella Tamburrino, Diego Tarrío, Giorgios Tsiledakis, Stanislav Valenta, Pedro Vaz, Gianfranco Vecchio, Diego Vescovi, Vasilis Vlachoudis, Rosa Vlastou, Anton Wallner, Christina Weiss, Tobias Wright, Renjie Wu, Roberto Zarrella and Petar Žugec Show full author list Hide full author list

Galaxies 2026, 14(3), 59; https://doi.org/10.3390/galaxies14030059 - 9 Jun 2026

Abstract

Neutron capture reactions provide essential nuclear physics input for modeling the synthesis of heavy elements in stars. The growing precision of stellar spectroscopy and isotopic measurements in presolar SiC grains now demands cross sections with improved accuracy over the full energy range, and [...] Read more.

Neutron capture reactions provide essential nuclear physics input for modeling the synthesis of heavy elements in stars. The growing precision of stellar spectroscopy and isotopic measurements in presolar SiC grains now demands cross sections with improved accuracy over the full energy range, and access to unstable nuclei relevant to slow (s-) process branchings and the intermediate (i-) process. This article reviews recent progress in direct neutron capture measurements, focusing on time-of-flight (TOF) experiments at CERN n_TOF and complementary activation techniques. Substantial advances have been achieved for stable s-only and bottleneck isotopes, significantly improving constraints on s-process models. In parallel, the combination of high instantaneous neutron fluxes and advanced detector systems has facilitated first-time neutron capture measurements on several radioactive branching-point nuclei. Feasibility studies, however, reveal current limitations related to sample availability, background conditions, and restricted energy coverage. In this context, the complementarity between TOF and activation emerges as a central strategy. Future developments, including high-flux facilities and novel inverse kinematics experiments in ion storage rings, are expected to extend the boundaries of neutron capture measurements, overcoming current limitations and helping unlock new frontiers in our understanding of stellar nucleosynthesis. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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16 pages, 760 KB

Open AccessReview

Neutron Capture in Evolved Red Giants: A Review

by Maurizio Maria Busso

Galaxies 2026, 14(3), 58; https://doi.org/10.3390/galaxies14030058 - 1 Jun 2026

Abstract

This review traces how our understanding of low- and intermediate-mass stars (hereafter LMS and IMS, respectively) evolved in time, in parallel with our knowledge of slow neutron-capture phenomena (the s-process). I shall focus in particular on the main component of this nucleosynthesis [...] Read more.

This review traces how our understanding of low- and intermediate-mass stars (hereafter LMS and IMS, respectively) evolved in time, in parallel with our knowledge of slow neutron-capture phenomena (the s-process). I shall focus in particular on the main component of this nucleosynthesis phenomenon, occurring in the above-mentioned stars close to the end of their lifetimes. They start ascending the Asymptotic Giant Branch (AGB), where both H- and He-shells exist, burning alternatively during the phases most relevant to our discussion: the so-called thermal pulses (hence, the name of TP-AGB stages for the final evolutionary period of these stars). I shall outline how such final stages were discovered to be a crucial source for neutron captures. Finally, I will briefly discuss what observational constraints and nuclear measurements have taught us about the status of our theoretical models in this field of nuclear and stellar physics. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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56 pages, 2421 KB

Open AccessReview

Flux and Spectral Variability of High-Energy-Peaked BL Lacertae Objects in the 0.3–10 keV Band

by Bidzina Kapanadze

Galaxies 2026, 14(3), 57; https://doi.org/10.3390/galaxies14030057 - 25 May 2026

Abstract

BL Lacertae objects (BL Lacs) are active galactic nuclei notable for beamed emission generated in the relativistic jets, forming a small angle with respect to our line-of-sight. The broadband spectra of BL Lacs show a two-component spectral energy distribution (SED). The group of [...] Read more.

BL Lacertae objects (BL Lacs) are active galactic nuclei notable for beamed emission generated in the relativistic jets, forming a small angle with respect to our line-of-sight. The broadband spectra of BL Lacs show a two-component spectral energy distribution (SED). The group of high-energy-peaked BL Lacs (HBLs) exhibit their lower-energy SED peak at the UV to X-ray frequencies. Consequently, these objects are generally bright in the 0.3–10 keV band (compared to other blazar subclasses) and allow us to carry out intense timing/spectral studies on the wide range of timescales (from years down to a few minutes). Although X-ray emission of HBLs is widely accepted to have a synchrotron origin (along with the occasional presence of the inverse-Compton component), many problems associated with the jet particle content, their acceleration up to ultra-relativistic energies and unstable mechanisms responsible for the extreme flux/spectral variability still remain to be solved. This review highlights the basic timing and polarimetric and spectral results obtained in the framework of the numerous studies of HBLs in the 0.3–10 keV band, which was covered by the X-ray instruments operating onboard the different space missions. Moreover, the plausible physical processes responsible for the observed HBL features (relativistic shocks, magnetic reconnection, turbulence etc.) are also addressed. Full article

(This article belongs to the Special Issue Multiwavelength Variability and Unstable Processes in High-Energy-Peaked BL Lacertae Objects)

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68 pages, 37071 KB

Open AccessReview

A Review of Space Energy Supply Technologies for Human Space Exploration Activities

by Bo Liu, Guoqing Zhang, Chang Wang, Lei Song and Le Ouyang

Galaxies 2026, 14(3), 56; https://doi.org/10.3390/galaxies14030056 - 25 May 2026

Abstract

Space energy supply is critical for human space exploration, serving as the foundation to support long-term space missions and future permanent settlement beyond Earth. To date, humanity has developed a variety of technologies for space energy supply. However, due to the constraints of [...] Read more.

Space energy supply is critical for human space exploration, serving as the foundation to support long-term space missions and future permanent settlement beyond Earth. To date, humanity has developed a variety of technologies for space energy supply. However, due to the constraints of the space environment and the diversity of energy sources, the energy supply technologies adopted by space exploration missions mainly depend on the feasibility of energy acquisition. This review presents a systematic review of the technical principles, power supply devices, and practical applications of space energy supply systems. First, this review summarizes the technologies for space-based solar power generation and energy storage, as well as strategies for improving the efficiency of solar power generation in space. Next, an overview of dynamic power generation technologies and static power systems for space thermal energy is investigated, along with a performance evaluation comparing these two types of systems. Subsequently, the work reviews space nuclear power systems based on thermoelectric generation technology, discusses recent advancements in nuclear fusion research, and analyzes the feasibility of utilizing helium-3 (³He) fusion technology on the Moon. Finally, to address the challenges associated with the storage and transportation of space energy, the review also introduces the applications of battery and fuel cell technologies in space. This review also discusses the technical challenges faced by space energy supply systems and explores future development prospects, aiming to provide a reference for the comprehensive development and utilization of space energy in the future. Full article

(This article belongs to the Collection A Trip across the Universe: Our Present Knowledge and Future Perspectives)

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30 pages, 2286 KB

Open AccessReview

A Review on Resolving the Hubble Tension via Late-Universe Physics

by Xuan-Dong Jia, Xin-Yi Dai, Yu-Peng Yang and Fa-Yin Wang

Galaxies 2026, 14(3), 55; https://doi.org/10.3390/galaxies14030055 - 22 May 2026

Abstract

The

Λ

CDM cosmological model has been successful in explaining many astronomical observations. However, recent observations increasingly point to deviations from the standard

Λ

CDM framework. Among these, one of the most significant discrepancies is the Hubble tension, which refers to the [...] Read more.

The

Λ

CDM cosmological model has been successful in explaining many astronomical observations. However, recent observations increasingly point to deviations from the standard

Λ

CDM framework. Among these, one of the most significant discrepancies is the Hubble tension, which refers to the difference in values obtained for the Hubble constant

H_{0}

from high-redshift measurement and local observation. To address this issue, numerous cosmological models and methodological approaches have been proposed. This review offers a concise overview of recent progress in resolving the Hubble tension. The combination of Dark Energy Spectroscopic Instrument (DESI) Baryon Acoustic Oscillations (BAO) and uncalibrated Type Ia supernovae data yields a value for

H_{0}

that is significantly higher than the

Λ

CDM predication based on early-universe probes, even without incorporating local distance ladder constraints. This result indicates that the origin of the Hubble tension lies in new physics at low redshifts. Our findings suggest that although many unresolved systematics persist in current observations, they are insufficient to account for the magnitude of the current Hubble tension. This implies the likely existence of new physical mechanisms that have yet to be discovered. Full article

(This article belongs to the Special Issue Theoretical and Observational Approaches to the Hubble Tension in Cosmology)

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29 pages, 2051 KB

Open AccessReview

Optical Variability of HBLs on Diverse Timescales

by Ileana Andruchow, Ezequiel J. Marchesini and Florencia L. Vieyro

Galaxies 2026, 14(3), 54; https://doi.org/10.3390/galaxies14030054 - 20 May 2026

Abstract

Since their discovery almost 60 years ago, BL Lac objects have been defined by their strong optical variability and their classification in the spectral energy distribution scheme. High-synchrotron-peaked BL Lacs (HBLs) are those whose synchrotron component peaks at frequencies higher than UV/X-rays. Historically, [...] Read more.

Since their discovery almost 60 years ago, BL Lac objects have been defined by their strong optical variability and their classification in the spectral energy distribution scheme. High-synchrotron-peaked BL Lacs (HBLs) are those whose synchrotron component peaks at frequencies higher than UV/X-rays. Historically, optical variability studies have focused mostly on their counterparts, low-synchrotron-peaked BL Lacs (LBLs), since HBLs have shown weaker optical variability. However, a population-wide study of HBL optical variability is still lacking, and it remains unclear whether HBLs are intrinsically less optically variable as a class or whether this reflects observational biases. Only a handful of HBL sources have been studied extensively due to their strong variability and reported periodicity. These sources have motivated several theoretical models, often conflicting, to explain the optical variability when present. Nevertheless, understanding the connection between the apparent weaker optical variability and the emission processes of HBLs remains a challenge. In this work, we review the current state of knowledge on this topic, with the expectation that upcoming optical monitoring observatories, such as the Vera C. Rubin, will provide new insights into the optical emission (and variability) mechanisms in HBLs. Full article

(This article belongs to the Special Issue Multiwavelength Variability and Unstable Processes in High-Energy-Peaked BL Lacertae Objects)

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20 pages, 2532 KB

Open AccessReview

Interstellar Filament Detection and Characterization: Methods and Implications for Studies of the Magnetized Interstellar Medium

by Dana Alina

Galaxies 2026, 14(3), 53; https://doi.org/10.3390/galaxies14030053 - 18 May 2026

Abstract

Filamentary structures are ubiquitous in the interstellar medium and play a key role in the evolution of molecular clouds and star formation. Their morphology and relative orientation with respect to magnetic fields have been widely used as a diagnostic of magnetohydrodynamic processes, turbulence, [...] Read more.

Filamentary structures are ubiquitous in the interstellar medium and play a key role in the evolution of molecular clouds and star formation. Their morphology and relative orientation with respect to magnetic fields have been widely used as a diagnostic of magnetohydrodynamic processes, turbulence, and gravitational accretion. In recent years, the growing availability of large continuum, spectroscopic, and polarization data stimulated the development of various filament detection techniques. In this review, we present a systematic overview of filament detection methods applied to observations of the interstellar medium. We classify the existing approaches into methodological categories, discuss underlying principles, illustrate their application on a same observational field, discuss limitations and advantages, in particular with respect to the studies of the relative alignment between magnetic fields and filaments. We conclude with presenting a point of view on the perspectives for filament studies in the era of ever-growing astronomical data volume. Full article

(This article belongs to the Special Issue Astrophysical Magnetohydrodynamics, Plasma Physics and Cosmic Rays)

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11 pages, 709 KB

Open AccessCommunication

Long-Lived Merger Signatures in the Perseus Cluster and a Candidate Remnant Interpretation

by Shawn Hackett

Galaxies 2026, 14(3), 52; https://doi.org/10.3390/galaxies14030052 - 18 May 2026

Abstract

Weak-lensing observations of the Perseus Cluster now indicate a massive sub-halo associated with NGC 1264 and a connecting mass bridge in a system long treated as a benchmark relaxed cool-core cluster. Perseus is also known from X-ray observations to host large-scale gas sloshing [...] Read more.

Weak-lensing observations of the Perseus Cluster now indicate a massive sub-halo associated with NGC 1264 and a connecting mass bridge in a system long treated as a benchmark relaxed cool-core cluster. Perseus is also known from X-ray observations to host large-scale gas sloshing and an ancient cold front extending to several hundred kiloparsecs. This paper uses Perseus as a motivation for a narrower population question: do nominally relaxed clusters retain merger history information in residual mass–gas offsets after the obvious signatures of an active merger have faded? A candidate remnant stress–energy interpretation is introduced as one possible covariant language for such a long-lived structure, but the empirical test does not require acceptance of that interpretation. The work then carries out a literature-based pilot test using the cold front outer radius as an independent merger history proxy, published mass–gas or gas tracer offsets for relaxed/cool-core systems, and a separate control cohort of actively dissociative mergers. The resulting three-regime comparison separates young active mergers, relaxed low-offset systems, and relaxed systems with sourced offsets above 5 kpc. For all seven Regime 3 (relaxed, offset

> 5

kpc) systems with vetted cold front/history proxies and sourced mass–gas offset measurements, the directional rank-order association has the predicted sign,

ρ_{s} = 0.68

, with

p_{one-sided} \approx 0.047

(

p_{two-sided} \approx 0.094

,

N = 7

). The one-sided statistic crosses the conventional

5 %

threshold. The sample mixes lensing–X-ray centroid offsets, BCG/X-ray peak offsets, and weak-lensing sub-halo separations, and the result is not a decisive population detection: it is a suggestive directional signal in a small heterogeneous archival pilot. Its significance is that a framework-derived directional diagnostic, specified before the sample was assembled, is non-zero in the predicted sense and can now be tested with a homogeneous weak-lensing/X-ray/SZ survey. Full article

(This article belongs to the Topic Dark Matter, Dark Energy and Cosmological Anisotropy)

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14 pages, 565 KB

Open AccessArticle

Photometric Metallicity of Galactic RR Lyrae Stars in the Gaia DR3 Era

by Mahiguhappriya Prakash, Susmita Das, Harinder P. Singh and Nitesh Kumar

Galaxies 2026, 14(3), 51; https://doi.org/10.3390/galaxies14030051 - 17 May 2026

Abstract

RR Lyrae stars are pulsating variables crucial for distance determination and galactic structure studies. Metallicities of fundamental-mode (RRab) RR Lyrae stars are commonly derived from photometry using empirical relations involving the Fourier parameter

ϕ_{31}

and the pulsation period. We present a new, [...] Read more.

RR Lyrae stars are pulsating variables crucial for distance determination and galactic structure studies. Metallicities of fundamental-mode (RRab) RR Lyrae stars are commonly derived from photometry using empirical relations involving the Fourier parameter

ϕ_{31}

and the pulsation period. We present a new, calibrated G-band relationship between pulsation period P, Fourier parameter

ϕ_{31}

, and metallicity [Fe/H] for galactic RR Lyrae stars from the Gaia survey. A set of 72 fundamental mode RR Lyrae stars were identified for deriving the relation in the G-band after visual examination of their light curves. Unlike recent large-scale calibrations, our relation prioritizes calibration purity by anchoring exclusively to a homogeneously analyzed sample of high-resolution spectroscopic metallicities from the literature. Our best fit relation is

[Fe / H] = (- 6.93 \pm 0.58) - (6.04 \pm 0.37) P + (1.65 \pm 0.11) ϕ_{31}

. We compare the [Fe/H] predicted by our relation for the stars in our calibration sample with that obtained from previously established relations in the G-band using different approaches. Our calibrated G-band P-

ϕ_{31}

-[Fe/H] relationship demonstrates high reliability when validated against spectroscopic data, achieving a negligible bias of 0.00 dex and an empirical RMS scatter of 0.26 dex. Furthermore, by applying an Orthogonal Distance Regression (ODR) routine that fully propagates parameter covariance, we establish a mathematically strict empirical baseline whose theoretical uncertainties perfectly align with this observed dispersion. We find that the inclusion of the

R_{21}

Fourier parameter offers no significant improvement in metallicity estimation. Comparisons with literature confirm that our linear relation aligns closely with other Gaia DR3-based studies, while offering improved precision over older DR2-based relations. Full article

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20 pages, 1395 KB

Open AccessReview

Spin Demographics of Active Supermassive Black Holes: Updated Estimates from X-Ray Reflection and Future Opportunities

by Júlia M. Sisk-Reynés, Christopher S. Reynolds, James H. Matthews, Dominic J. Walton, Joanna M. Piotrowska, James F. Steiner, Javier A. García and Angelo Ricarte

Galaxies 2026, 14(3), 50; https://doi.org/10.3390/galaxies14030050 - 15 May 2026

Abstract

Understanding the growth of supermassive black holes (SMBHs) requires observational constraints on how their angular momentum—or spin—varies with mass, since the relative importance of coherent accretion, chaotic accretion, and mergers will be reflected in SMBH spin populations. Here we present an updated compilation [...] Read more.

Understanding the growth of supermassive black holes (SMBHs) requires observational constraints on how their angular momentum—or spin—varies with mass, since the relative importance of coherent accretion, chaotic accretion, and mergers will be reflected in SMBH spin populations. Here we present an updated compilation of reflection-based SMBH spin measurements from the literature and assemble a set of ancillary quantities of interest for each SMBH (including redshift, Eddington ratio, and X-ray luminosity). No obvious apparent correlation between the Eddington-scaled accretion rate and the black hole spin is seen, noting that formal statistical tests are beyond the scope of this review. We discuss the limitations of using this heterogeneous mass–spin sample to test predictions of SMBH growth from semi-analytic models and cosmological simulations, emphasizing the need for a more uniform sample. We then highlight the encouraging prospects enabled by the next-generation NewAthena X-ray flagship observatory. Finally, we summarize how hierarchical Bayesian population inference applied to observed SMBH mass–spin populations will constitute a powerful framework for confirming tentative mass–spin trends in future samples. Full article

(This article belongs to the Special Issue Black Hole Spin Measurements)

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8 pages, 484 KB

Open AccessArticle

The Ba Isotopic Ratio as a Way of Distinguishing the R- and S-Process in Chemical Evolution Models

by Federico Rizzuti, Gabriele Cescutti, Linda Lombardo, Lorenzo Roberti and Tatyana Sitnova

Galaxies 2026, 14(3), 49; https://doi.org/10.3390/galaxies14030049 - 14 May 2026

Abstract

Only recently, observational studies have started providing measurements for the barium isotopic ratio in metal-poor stars with unprecedented detail. This new approach can be extremely useful in tracing back the origin of neutron-capture elements, since the r- and s-process produce different amounts of [...] Read more.

Only recently, observational studies have started providing measurements for the barium isotopic ratio in metal-poor stars with unprecedented detail. This new approach can be extremely useful in tracing back the origin of neutron-capture elements, since the r- and s-process produce different amounts of barium isotopes, and their astrophysical sites of production are still largely unconstrained. We employ here a stochastic chemical evolution model of the Galactic halo to compare observations to theoretical predictions. We find that in the earliest phases of evolution, both r- and s-process sites are required, with the model and observations agreeing well for Sr, Ba and Eu, possibly requiring a slightly larger s-process production for Sr. The model can actually explain the mixture of r- and s-process material often observed in halo stars. This work shows how is it possible now to use isotopic ratios in addition to elemental ratios to obtain additional constraints useful for the Galactic Archaeology investigation. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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41 pages, 1543 KB

Open AccessArticle

Analysing Hubble Tension and Gravitational Waves for f(Q,T) Gravity Theories

by Aritrya Paul and Shreya Banerjee

Galaxies 2026, 14(3), 48; https://doi.org/10.3390/galaxies14030048 - 14 May 2026

Abstract

In this work, we examine viable models of

f (Q, T)

gravity theories against observational data with the aim to constrain the parameter space of these models. We have analyzed four different models of

f (Q, T)

[...] Read more.

In this work, we examine viable models of

f (Q, T)

gravity theories against observational data with the aim to constrain the parameter space of these models. We have analyzed four different models of

f (Q, T)

gravity and tested them against against late-time background probes: Cosmic Chronometer (CC), Baryon Acoustic Oscillations (DESI BAO),

P a n t h e o n^{+}

and Gravitational wave(GWTC-3) data. We put stringent constraints on the

f (Q, T)

gravity models,

f (Q, T) = α Q + β T

,

f (Q, T) = α Q^{n} + β T

,

f (Q, T) = - α Q - β T^{2}

and

f (Q, T) = α Q^{- 2} T^{2}

along with other late-time cosmological parameters such as deceleration parameter (

q_{0}

), equation of state parameter (

w_{0}

), sound horizon distance (

r_{d}

) and demonstrate their alignment with the

Λ C D M

model and the observational data. We show that these models have the capability to alleviate the Hubble tension in late time universe, by predicting the present value of the Hubble parameter close to 74 km/s/Mpc.

f (Q, T)

gravity theory introduces alterations in the background evolution and imposes a friction term in the propagation of gravitational waves, this phenomenon has also been examined. We have shown their agreement with the Gravitational Wave (GW) luminosity distance with the Electromagnetic (EM) counter part GWTC-3 data from Advanced LIGO and Advanced VIRGO across different observing runs capturing coalescence of Binary Neutron Stars (BNS), mergers of Binary Black Holes (BBHs), and Neutron Star-Black Hole (NSBH) binaries with EM counterparts. Full article

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8 pages, 2143 KB

Open AccessArticle

Nucleosynthesis of Elements Beyond Fe in C-O Shell Mergers

by Lorenzo Roberti, Agnese Falla and Luca Boccioli

Galaxies 2026, 14(3), 47; https://doi.org/10.3390/galaxies14030047 - 14 May 2026

Abstract

Carbon–oxygen (C–O) shell mergers in the final evolutionary stages of massive stars play a critical role in shaping the pre-supernova structure and the resulting nucleosynthesis. In this work, we investigate the impact of such a merger on the production of elements beyond the [...] Read more.

Carbon–oxygen (C–O) shell mergers in the final evolutionary stages of massive stars play a critical role in shaping the pre-supernova structure and the resulting nucleosynthesis. In this work, we investigate the impact of such a merger on the production of elements beyond the Iron peak, focusing on an extremely metal-poor (

[Fe / H] = - 5

) rotating 15

M_{⊙}

stellar model. The results show that the merger favors the synthesis of weak s-process seeds and light p-nuclei, such as ⁸⁸Sr, ⁹⁴Mo, and ⁹⁸Ru, via photodisintegration of heavier nuclei previously produced by rotational-induced nucleosynthesis. By simulating the subsequent core-collapse supernova explosion with a thermal bomb approach, we demonstrate that these chemical signatures are largely preserved, as the expanded structure of the merged shells significantly modifies the impact of the shock wave. These findings suggest that C–O shell mergers in early-generation stars could provide a primary-like source for intermediate and heavy elements, with important implications for the chemical evolution of the early Universe. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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13 pages, 1405 KB

Open AccessArticle

Just Beyond the S-Process Termination Point: Nucleosynthesis of Lead–Bismuth Cyclic Reactions

by Nurzat Kenzhebayev, Manas Khassanov, Ruslan Spassyuk, Daulet Anarbek, Yerlan Aimuratov and Medeu Abishev

Galaxies 2026, 14(3), 46; https://doi.org/10.3390/galaxies14030046 - 14 May 2026

Abstract

We examine cyclic nuclear reactions in the lead–bismuth (Pb–Bi) system near the s-process termination point. We present a numerical investigation of the isotopic evolution and decay heat generation in an extended 60-isotope nuclear reaction network under continuous 30 keV neutron irradiation ( [...] Read more.

We examine cyclic nuclear reactions in the lead–bismuth (Pb–Bi) system near the s-process termination point. We present a numerical investigation of the isotopic evolution and decay heat generation in an extended 60-isotope nuclear reaction network under continuous 30 keV neutron irradiation (

10^{14}

–

10^{28}

n cm⁻² s⁻¹) using the Chebyshev Rational Approximation Method (CRAM). The network accounts for 88 transitions, utilising a hybrid data approach that combines neutron capture cross-sections from EAF-2010 and TALYS with fundamental decay properties from the ENDF/B-VIII.0. Our simulations reveal two distinct evolutionary regimes. At moderate fluxes (

10^{14}

–

10^{20}

n cm⁻² s⁻¹), the system establishes a steady cyclic loop driven by the

α

-decay of

{}^{210}{Po}

, successfully reproducing the s-process termination isotopic distribution (

{}^{208}{Pb} ≫^{209} Bi >^{207} Pb >^{206} Pb

), characteristic of low-metallicity AGB stars. As the flux exceeds

10^{22}

n cm⁻² s⁻¹, the classical balance breaks down, propelling mass flow toward heavier trace isotopes and suggesting a potential transition into the intermediate neutron capture (i-process) regime. Heat density calculations demonstrate that while the energy release of the core cycle plateaus near

10^{5}

W cm⁻³, the extended chain drives an energy surge to over

10^{8}

W cm⁻³ at

10^{24}

n cm⁻² s⁻¹ before the system enters an unstable transient state at extreme fluxes. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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41 pages, 770 KB

Open AccessReview

TeV-Band Properties of Nearby HBLs

by Bidzina Kapanadze and Stefano Vercellone

Galaxies 2026, 14(3), 45; https://doi.org/10.3390/galaxies14030045 - 13 May 2026

Abstract

Nearby (

z < 0.1

) TeV-detected, high-energy-peaked BL Lacertae objects (HBLs) are among the most prominent extragalactic sources of the highest-energy photons, sometimes detected at energies of ∼10 TeV or beyond. These objects show a strong and complex flux variability, with strong [...] Read more.

Nearby (

z < 0.1

) TeV-detected, high-energy-peaked BL Lacertae objects (HBLs) are among the most prominent extragalactic sources of the highest-energy photons, sometimes detected at energies of ∼10 TeV or beyond. These objects show a strong and complex flux variability, with strong flares and exceptional outbursts, as well as very rapid and large-amplitude TeV-band variations on timescales down to a few minutes during such instances. The higher-energy component of broadband spectral energy distribution (SED) is stretched over the MeV–TeV domain and, generally peaking beyond 100 GeV, has a controversial origin, and different emission scenarios (one- or multi-zone synchrotron self-Compton, hadronic cascades, etc.) are proposed. This paper presents a review of the TeV-band timing and spectral results obtained in the framework of different observational campaigns for nearby HBLs, their implications for different emission scenarios, and basic results from the corresponding SED modelings. Finally, the prospect of filling the observational gaps above some threshold energy by means of the planned projects for the dedicated

γ

-ray observations and, consequently, solving the different persisting problems related to the innermost structure, particle acceleration, and emission mechanisms are also presented. Full article

(This article belongs to the Special Issue Multiwavelength Variability and Unstable Processes in High-Energy-Peaked BL Lacertae Objects)

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12 pages, 1108 KB

Open AccessReview

Can Neutron-Capture Products Constrain the Origin of Life on Earth?

by Katherine R. Bermingham and Bradley S. Meyer

Galaxies 2026, 14(3), 44; https://doi.org/10.3390/galaxies14030044 - 12 May 2026

Abstract

Neutron-capture products, such as molybdenum (Mo) isotopes, are an important tool that cosmochemists use to constrain the stellar precursors of the Solar System and, potentially, the origin of life on Earth. Using high-precision Mo isotope data from meteorites and terrestrial samples, studies have [...] Read more.

Neutron-capture products, such as molybdenum (Mo) isotopes, are an important tool that cosmochemists use to constrain the stellar precursors of the Solar System and, potentially, the origin of life on Earth. Using high-precision Mo isotope data from meteorites and terrestrial samples, studies have attempted to reconstruct Earth’s formation by linking its composition to material sourced from various heliocentric distances. Debate, however, persists about the nature of Earth’s late-stage building blocks that accreted around the time the Moon formed and whether they delivered life-essential elements (i.e., carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur; CHNOPS), which are presumed to be more prevalent in the outer Solar System. Initially, it was proposed that the Moon-forming event involved the addition of material from both the inner and outer Solar System, thereby providing a mechanism for the delivery of a significant portion of life-bearing elements late in Earth’s formation. Recent advancements in analytical chemistry and their application to a wider range of samples than previously studied, however, led to a revised constraint: the Moon-forming event was dominated by inner Solar System material that was less enriched in CHNOPS, thereby relaxing the requirement for the delivery of a consequential amount of life-bearing elements late in Earth’s formation. A review of analytical approaches and findings is presented here to highlight the utility of neutron-capture products in constraining the origin of life on Earth. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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12 pages, 1117 KB

Open AccessReview

Gamma Cassiopeiae: History and Mystery

by Olga A. Tsiopa, Alexander F. Kholtygin and Petr K. Tsiopa

Galaxies 2026, 14(3), 43; https://doi.org/10.3390/galaxies14030043 - 8 May 2026

Abstract

The history of observations of gamma Cassiopeiae (

γ

Cas) is presented, including references to Soviet-era papers that have not been translated into English. The current state of knowledge is discussed. Particular attention is paid to the period of significant changes in the [...] Read more.

The history of observations of gamma Cassiopeiae (

γ

Cas) is presented, including references to Soviet-era papers that have not been translated into English. The current state of knowledge is discussed. Particular attention is paid to the period of significant changes in the system’s characteristics during the 1930s and 1940s. Full article

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18 pages, 1363 KB

Open AccessArticle

Ba Isotope Ratio in CEMP-s and CEMP-rs Stars as a Signature of s-Process and i-Process

by Tatyana Sitnova and Lyudmila Mashonkina

Galaxies 2026, 14(3), 42; https://doi.org/10.3390/galaxies14030042 - 6 May 2026

Abstract

We present a spectroscopic analysis of three carbon-enhanced metal-poor (CEMP) stars of type CEMP-s and CEMP-rs and determine their non-local thermodynamic equilibrium (NLTE) abundances of Ba and the fractions of the odd Ba isotopes (

F_{odd}

). We found

F_{odd}

= [...] Read more.

We present a spectroscopic analysis of three carbon-enhanced metal-poor (CEMP) stars of type CEMP-s and CEMP-rs and determine their non-local thermodynamic equilibrium (NLTE) abundances of Ba and the fractions of the odd Ba isotopes (

F_{odd}

). We found

F_{odd}

= 0.

65_{- 0.34}^{+ 0.35}

in SDSS J1349-0229, which is known in the literature as a CEMP-rs star, while the other two stars, BPS CS 29512-073 and SDSS J1036+1212, exhibit lower

F_{odd}

= 0.

23_{- 0.10}^{+ 0.19}

and 0.

23_{- 0.11}^{+ 0.22}

, respectively, and they are known in the literature as CEMP-s stars. The present result supports our earlier finding about distinct

F_{odd}

in CEMP-s and CEMP-rs stars. For obtaining observational constraints on i-process nucleosynthesis, further NLTE abundance determinations for many chemical elements are required. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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