Universe

42 pages, 20041 KB

Open AccessArticle

A Systematic Search for New δ Scuti and γ Doradus Stars Using TESS Data

by Ai-Ying Zhou

Universe 2025, 11(9), 302; https://doi.org/10.3390/universe11090302 - 5 Sep 2025

Focusing on the discovery of new

δ

Scuti and

γ

Doradus stars, we analyzed the Transiting Exoplanet Survey Satellite (TESS) light curves for 193,940 A-F stars selected from four legacy catalogs—the Henry Draper Catalogue (HD), the Smithsonian Astrophysical Observatory (SAO) Star [...] Read more.

Focusing on the discovery of new

δ

Scuti and

γ

Doradus stars, we analyzed the Transiting Exoplanet Survey Satellite (TESS) light curves for 193,940 A-F stars selected from four legacy catalogs—the Henry Draper Catalogue (HD), the Smithsonian Astrophysical Observatory (SAO) Star Catalog, the Positions and Proper Motions Catalog (PPM), and the Bonner Durchmusterung (BD, including its extensions). Through visual inspection of light curve morphologies and periodograms, combined with evaluation of stellar parameters, we identified over 51,850 previously unreported variable stars. These include 15,380

δ

Scuti, 18,560

γ

Doradus, 28 RR Lyrae stars, 260 heartbeat candidates, and 2645 eclipsing binaries, along with thousands of other variable types. Notably, over 4145 variables exhibit hybrid

δ

Scuti-

γ

Doradus pulsations, and more than 380 eclipsing binaries feature pulsating primary components. This study reveals a substantial population of bright, previously undetected variables, providing a valuable resource for ensemble asteroseismology, binary evolution studies, and Galactic structure research. Our results also highlight the surprising richness in variability still hidden within well-known stellar catalogs and the continued importance of high-precision, time-domain surveys such as TESS. Full article

(This article belongs to the Section Solar and Stellar Physics)

76 pages, 17110 KB

Open AccessArticle

A Catalog of 73 B-Type Stars and Their Brightness Variation from k2 Campaign 13–18

by Bergerson V. H. V. da Silva, Jéssica M. Eidam, Alan W. Pereira, M. Cristina Rabello-Soares, Eduardo Janot-Pacheco, Laerte Andrade and Marcelo Emilio

Universe 2025, 11(9), 301; https://doi.org/10.3390/universe11090301 - 3 Sep 2025

Abstract

The variability of B-type stars offers valuable insights into the interiors of stars and the processes that drive pulsation and rotation in massive stars. In this study, we present the classification of the variability of 197 B-type stars observed in various Kepler/ [...] Read more.

The variability of B-type stars offers valuable insights into the interiors of stars and the processes that drive pulsation and rotation in massive stars. In this study, we present the classification of the variability of 197 B-type stars observed in various Kepler/K2 campaigns, including 73 newly classified stars from Campaigns 13–18. For these stars, we derived atmospheric and evolutionary parameters using space-based photometry and ground-based spectroscopy. We obtained spectroscopic data for 34 targets with high-resolution instruments at OPD/LNA, which were supplemented by archival LAMOST spectra. After correcting for instrumental systematics, we analyzed the light curves using Fourier transforms and wavelet decomposition to identify both periodic and stochastic signals. The identified variability types included SPB stars,

β

Cephei/SPB hybrids, fast-rotating pulsators, stochastic low-frequency variables, eclipsing binaries, and rotational variables. We also revised classifications of misidentified stars using Gaia astrometry, confirming the main-sequence nature of objects once considered subdwarfs. Our results indicate that hot-star variability exists along a continuum shaped by mass, rotation, and internal mixing rather than distinct instability domains. This study enhances our understanding of B-type star variability and supports future asteroseismic modeling with missions like PLATO. Full article

(This article belongs to the Special Issue Variable Stars in the 21st Century: From Microvariability to Megavariability)

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13 pages, 324 KB

Open AccessArticle

Gauge Symmetry and Radiatively Induced Terms in Dimension-5 Non-Minimal Lorentz-Violating QED

by A. P. B. Scarpelli and A. R. Vieira

Universe 2025, 11(9), 300; https://doi.org/10.3390/universe11090300 - 3 Sep 2025

Abstract

In this work, we derive the conditions that ensure gauge invariance of non-minimal dimension-5 Lorentz-violating QED. The two- and three-point functions at one loop are computed. The gauge Ward identities are checked, as well as the conditions, to ensure that the gauge symmetry [...] Read more.

In this work, we derive the conditions that ensure gauge invariance of non-minimal dimension-5 Lorentz-violating QED. The two- and three-point functions at one loop are computed. The gauge Ward identities are checked, as well as the conditions, to ensure that the gauge symmetry of this non-minimal framework is found to be the same of the usual QED. Induced terms are also investigated, and it is shown that the non-minimal Lorentz-violating

a_{F}^{(5)}

-term of the fermion sector can radiatively induce a non-minimal Lorentz-violating term in the photon sector. Full article

(This article belongs to the Section Field Theory)

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4 pages, 154 KB

Open AccessEditorial

Editorial for the Special Issue “New Discoveries in Astronomical Data”

by Yanxia Zhang and A-Li Luo

Universe 2025, 11(9), 299; https://doi.org/10.3390/universe11090299 - 3 Sep 2025

Abstract

Over the past decade, astronomy has shifted from a data-starved to a data-drenched science [...] Full article

(This article belongs to the Special Issue New Discoveries in Astronomical Data)

1 pages, 159 KB

Open AccessCorrection

Correction: Kuić et al. Finite Time Path Field Theory and a New Type of Universal Quantum Spin Chain Quench Behavior. Universe 2025, 11, 230

by Domagoj Kuić, Alemka Knapp and Diana Šaponja-Milutinović

Universe 2025, 11(9), 298; https://doi.org/10.3390/universe11090298 - 2 Sep 2025

Viewed by 62

Abstract

We would like to report an error in the published paper [...] Full article

9 pages, 1664 KB

Open AccessArticle

Quantized Nuclear Recoil in the Search for Sterile Neutrinos in Tritium Beta Decay with PTOLEMY

by Wonyong Chung, Mark Farino, Andi Tan, Christopher G. Tully and Shiran Zhang

Universe 2025, 11(9), 297; https://doi.org/10.3390/universe11090297 - 2 Sep 2025

Viewed by 149

Abstract

The search for keV-scale sterile neutrinos in tritium beta decay is made possible through the theoretically allowed small admixture of electron flavor in right-handed, singlet, massive neutrino states. A distinctive feature of keV-scale sterile-neutrino–induced threshold distortions in the tritium beta spectrum is the [...] Read more.

The search for keV-scale sterile neutrinos in tritium beta decay is made possible through the theoretically allowed small admixture of electron flavor in right-handed, singlet, massive neutrino states. A distinctive feature of keV-scale sterile-neutrino–induced threshold distortions in the tritium beta spectrum is the presence of quantized nuclear-recoil effects, as predicted for atomic tritium bound to two-dimension materials such as graphene. The sensitivities to the sterile neutrino mass and electron-flavor mixing are considered in the context of the PTOLEMY detector simulation with tritiated graphene substrates. The ability to scan the entire tritium energy spectrum with a narrow energy window, low backgrounds, and high-resolution differential energy measurements provides the opportunity to pinpoint the quantized nuclear-recoil effects. providing an additional tool for identifying the kinematics of the production of sterile neutrinos. Background suppression is achieved by transversely accelerating electrons into a high magnetic field, where semi-relativistic electron tagging can be performed with cyclotron resonance emission RF antennas followed by deceleration through the PTOLEMY filter into a high-resolution differential energy detector operating in a zero-magnetic-field region. The PTOLEMY-based approach to keV-scale searches for sterile neutrinos involves a novel precision apparatus utilizing two-dimensional materials to yield high-resolution, sub-eV mass determination for electron-flavor mixing fractions of

| U_{e 4} |^{2} ≃ 10^{- 5}

and smaller. Full article

(This article belongs to the Special Issue keV Warm Dark Matter (ΛWDM) in Agreement with Observations in Tribute to Héctor J. de Vega (2nd Edition))

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10 pages, 21975 KB

Open AccessArticle

A Comparison Study of Collisions at Relativistic Energies Involving Light Nuclei

by Hai-Cheng Wang, Song-Jie Li, Jun Xu and Zhong-Zhou Ren

Universe 2025, 11(9), 296; https://doi.org/10.3390/universe11090296 - 1 Sep 2025

Viewed by 94

Abstract

We present extensive comparisons of ¹⁶O+¹⁶O collisions at a center-of-mass energy per nucleon pair

\sqrt{s_{N N}} = 200

GeV and ²⁰⁸Pb+¹⁶O collisions at

\sqrt{s_{N N}} = 68.5

GeV as well as ²⁰Ne+²⁰Ne [...] Read more.

We present extensive comparisons of ¹⁶O+¹⁶O collisions at a center-of-mass energy per nucleon pair

\sqrt{s_{N N}} = 200

GeV and ²⁰⁸Pb+¹⁶O collisions at

\sqrt{s_{N N}} = 68.5

GeV as well as ²⁰Ne+²⁰Ne collisions at

\sqrt{s_{N N}} = 200

GeV and ²⁰⁸Pb+²⁰Ne collisions at

\sqrt{s_{N N}} = 68.5

GeV based on a multiphase transport (AMPT) model. We recommend measuring the ratio of the elliptic flow to the triangular flow, which shows appreciable sensitivity to the structure of light nuclei, as also found in other studies. This is especially so if the observable is measured near the target rapidity in ²⁰⁸Pb+¹⁶O or ²⁰⁸Pb+²⁰Ne collisions, as originally found in the present study. Our study serves as a useful reference for understanding the effect of structure on observables in collisions involving light nuclei under analysis or on the schedule. Full article

(This article belongs to the Special Issue Relativistic Heavy-Ion Collisions: Theory and Observation)

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20 pages, 16141 KB

Open AccessArticle

Low-Latitude Ionospheric Anomalies During Geomagnetic Storm on 10–12 October 2024

by Plamen Mukhtarov and Rumiana Bojilova

Universe 2025, 11(9), 295; https://doi.org/10.3390/universe11090295 - 1 Sep 2025

Viewed by 120

Abstract

This research examines in detail the behavior of the Equatorial Ionization Anomaly (EIA) during a severe geomagnetic storm that occurred on 10–11 October 2024. The global data of Total Electron Content (TEC) represented by relative deviation, giving information about the variations compared to [...] Read more.

This research examines in detail the behavior of the Equatorial Ionization Anomaly (EIA) during a severe geomagnetic storm that occurred on 10–11 October 2024. The global data of Total Electron Content (TEC) represented by relative deviation, giving information about the variations compared to quiet conditions, were used. The main attention is paid to the appearance of an additional “fountain effect” under the action of disturbed dynamo currents and the vertical drift of the ionospheric plasma caused by them. The results show that the area in which a positive response (increase) of TEC is observed occurs in an area corresponding to local time around 18–20 h (longitude around 60 °W) at magnetic latitudes ±30° and during the storm shifts westward to around 180 °W. The westward drift of the storm-induced “fountain effect” is moving at a speed much slower than the Earth’s rotation speed. As a result, the area of positive TEC response (vertical upward drift) and the area of negative response (vertical downward drift) are localized in both nighttime and daytime conditions. In this investigation, an example of a very similar geomagnetic storm registered on 25 September 1998 is given for comparison, in which a similar stationing of the storm-induced EIA was observed at longitudes around 180 °E. Full article

(This article belongs to the Section Space Science)

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11 pages, 711 KB

Open AccessCommunication

What Do Radio Emission Constraints Tell Us About Little Red Dots as Tidal Disruption Events?

by Krisztina Perger, Judit Fogasy and Sándor Frey

Universe 2025, 11(9), 294; https://doi.org/10.3390/universe11090294 - 1 Sep 2025

Viewed by 208

Abstract

The real nature of little red dots (LRDs), a class of very compact galaxies in the early Universe recently discovered by the James Webb Space Telescope, is still poorly understood. The most popular theories competing to interpret the phenomena include active galactic nuclei [...] Read more.

The real nature of little red dots (LRDs), a class of very compact galaxies in the early Universe recently discovered by the James Webb Space Telescope, is still poorly understood. The most popular theories competing to interpret the phenomena include active galactic nuclei and enhanced star formation in dusty galaxies. To date, however, neither model gives a completely satisfactory explanation to the population as a whole; thus, alternative theories have arisen, including tidal disruption events (TDEs). By considering observational constraints on the radio emission of LRDs, we discuss whether TDEs are adequate alternatives solving these high-redshift enigmas. We utilise radio flux density upper limits from LRD stacking analyses, TDE peak radio luminosities, and volumetric density estimates. We find that the characteristic values of flux densities and luminosities allow radio-quiet TDEs as the underlying process of LRDs in any case, while the less common radio-loud TDEs are compatible with the model under special constraints only. Considering other factors, such as volumetric density estimates, delayed and long-term radio flares of TDEs, and cosmological time dilation, TDEs appear to be a plausible explanation for LRDs from the radio point of view. Full article

(This article belongs to the Special Issue Advances in Studies of Galaxies at High Redshift)

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11 pages, 407 KB

Open AccessCommunication

On Restrictions of Current Warp Drive Spacetimes and Immediate Possibilities of Improvement

by Hamed Barzegar and Thomas Buchert

Universe 2025, 11(9), 293; https://doi.org/10.3390/universe11090293 - 1 Sep 2025

Viewed by 162

Abstract

Looking at current proposals of so-called ‘warp drive spacetimes’, they appear to employ General Relativity only at an elementary level. A number of strong restrictions are imposed such as flow-orthogonality of the spacetime foliation, vanishing spatial Ricci tensor, and dimensionally reduced and coordinate-dependent [...] Read more.

Looking at current proposals of so-called ‘warp drive spacetimes’, they appear to employ General Relativity only at an elementary level. A number of strong restrictions are imposed such as flow-orthogonality of the spacetime foliation, vanishing spatial Ricci tensor, and dimensionally reduced and coordinate-dependent velocity fields, to mention the main restrictions. We here provide a brief summary of our proposal of a general and covariant description of spatial motions within General Relativity, then discuss the restrictions that are employed in the majority of the current literature. That current warp drive models are discussed to be unphysical may not be surprising; they lack important ingredients such as covariantly non-vanishing spatial velocity, acceleration, vorticity together with curved space, and a warp mechanism. Full article

(This article belongs to the Special Issue Celebrating the 110th Anniversary of General Relativity: Advances, Challenges and Perspectives)

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15 pages, 425 KB

Open AccessArticle

Application of the Magnetar Engine to an Intermediate-Luminosity Gamma-Ray Burst Associated with the Supernova GRB 201015A/SN 201015A

by Xingling Li, Defeng Kong, Liangjun Chen, Xianggao Wang and Enwei Liang

Universe 2025, 11(9), 292; https://doi.org/10.3390/universe11090292 - 31 Aug 2025

Viewed by 158

Abstract

We present optical photometry for the afterglow of GRB 201015A, which can be classified as a medium-luminosity gamma-ray burst (

L_{γ, iso} \approx 2.55 \times 10^{49} erg s^{- 1}

) and the associated underlying supernova SN 201015A. A millisecond [...] Read more.

We present optical photometry for the afterglow of GRB 201015A, which can be classified as a medium-luminosity gamma-ray burst (

L_{γ, iso} \approx 2.55 \times 10^{49} erg s^{- 1}

) and the associated underlying supernova SN 201015A. A millisecond magnetar engine has been widely suggested to exist in gamma-ray burst (GRB) phenomena. In this paper, we study the effects of the magnetar engine on GRB 201015A/SN 201015A by light curve analysis. We use a smooth broken power-law plus magnetar spin-down model to fit the X-ray and optical light curves of GRB 201015A/SN 201015A. The best-fitting results reveal that the magnetar initial spin period and surface magnetic field at the pole are constrained to be

P_{0} = 16 . 80_{- 0.47}^{+ 0.24} ms

and

B_{p} = 0 . 80_{- 0.32}^{+ 0.34} \times 10^{15} G

, respectively, and the SN ejected a total mass of

M_{ej} = 2 . 55_{- 0.37}^{+ 1.12} M_{⊙}

and an ejecta velocity of

v_{ej}

=

{30,000}_{- 2500}^{+ 4800} km s^{- 1}

, inferring a kinetic energy of

E_{SN, K} \approx 1.37 \times 10^{52} erg

. From our analysis, we find that the central engine of GRB 201015A/SN 201015A may well be a magnetar, and the emission from a magnetar central engine can be solely responsible for powering SN 201015A. Full article

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9 pages, 406 KB

Open AccessArticle

A Proposed Test for the Gravitational Tunnel Effect

by Alfonso González Jiménez, Enderson Falcón Gómez, Isabel Carnoto Amat and Luis Enrique García Muñoz

Universe 2025, 11(9), 291; https://doi.org/10.3390/universe11090291 - 28 Aug 2025

Viewed by 227

Abstract

This article addresses the problem of the tunnel effect with a gravitational potential. Specifically, the quasiclassical formulation is used here, and the Wentzel–Kramers–Brillouin approximation is applied to the potential. This allows the problem to be solved for different configurations with different values (masses, [...] Read more.

This article addresses the problem of the tunnel effect with a gravitational potential. Specifically, the quasiclassical formulation is used here, and the Wentzel–Kramers–Brillouin approximation is applied to the potential. This allows the problem to be solved for different configurations with different values (masses, distances, etc.). The chosen values are intended to provide a clear comparison when varying the different parameters. Furthermore, feasible values are considered for practically replicating the experiment without resorting to astrophysical methods. Due to the low intensity of the gravitational force, these experiments will be difficult to replicate, but it is possible to improve some parameters at the expense of others. Full article

(This article belongs to the Topic Quantum Systems and Their Applications)

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16 pages, 820 KB

Open AccessArticle

Exploring the Impact of Self-Excited Alfvén Waves on Transonic Winds: Applications in Galactic Outflows

by Bilal Ramzan, Syed Nasrullah Ali Qazi and Chung-Ming Ko

Universe 2025, 11(9), 290; https://doi.org/10.3390/universe11090290 - 26 Aug 2025

Viewed by 285

Abstract

The impact of cosmic rays is crucial to understand the energetic plasma outflows coming out from the Galactic centers against the strong gravitational potential well. Cosmic rays can interact with thermal plasma via streaming instabilities and produce hydromagnetic waves/fluctuations. During the propagation of [...] Read more.

The impact of cosmic rays is crucial to understand the energetic plasma outflows coming out from the Galactic centers against the strong gravitational potential well. Cosmic rays can interact with thermal plasma via streaming instabilities and produce hydromagnetic waves/fluctuations. During the propagation of cosmic rays it can effectively diffuse and advect through the thermal plasma which results the excitation of Alfvén waves. We are treating thermal plasma, cosmic rays and self-excited Alfvén waves as fluids and our model is referred as multi-fluid model. We investigate steady-state transonic solutions for four-fluid systems (with forward as well as backward propagating self-excited Alfvén waves) with certain boundary conditions at the base of the potential well. As a reference model, a four-fluid model with cosmic-ray diffusion, wave damping and cooling can be studied together and solution topology can be analyzed with different set of boundary conditions available at the base of the gravitational potential well. We compare cases with enhancing the backward propagating self-excited Alfvén waves pressure and examining the shifting of the transonic point near or far away from the base. In conclusion we argue that the variation of the back-ward propagating self-excited Alfvén waves significantly alters the transonic solutions at the base. Full article

(This article belongs to the Special Issue Studying Astrophysics with High-Energy Cosmic Particles)

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19 pages, 1865 KB

Open AccessArticle

Bayesian Analysis of the Nexus Paradigm Predictions for Supermassive Black Hole Observations by the Event Horizon Telescope

by Stuart Marongwe, Moletlanyi Tshipa and Christian Corda

Universe 2025, 11(9), 289; https://doi.org/10.3390/universe11090289 - 26 Aug 2025

Viewed by 492

Abstract

We present a Bayesian statistical analysis to evaluate the Nexus Paradigm (NP) of quantum gravity, using horizon-scale observations of supermassive black holes (SMBHs) Sagittarius A* (Sgr A*) and M87* from the Event Horizon Telescope (EHT). The NP predicts angular diameters for the dark [...] Read more.

We present a Bayesian statistical analysis to evaluate the Nexus Paradigm (NP) of quantum gravity, using horizon-scale observations of supermassive black holes (SMBHs) Sagittarius A* (Sgr A*) and M87* from the Event Horizon Telescope (EHT). The NP predicts angular diameters for the dark depression, emission ring, and base diameter, which we compare to EHT measurements. Employing Gaussian likelihoods and priors informed by mass-to-distance ratio uncertainties, we compute the posterior distribution for the angular scale parameter

θ_{g}

, achieving a combined

χ^{2} \approx 0.0062

(four degrees of freedom) corresponding to a 4.37

σ

(99.9972%) confidence level. Individual features show deviations

< 0.1 σ

supporting the NP’s claim of 99th percentile agreement. Compared to General Relativity (GR), which predicts a shadow diameter inconsistent with the observed dark depression (

χ^{2} \approx 168, ~ 12.97 σ

) the NP is favored with a Bayes factor of

~ 10^{36}

. These results validate the NP’s predictions and highlight its potential as a quantum gravity framework, though refined uncertainties and broader model comparisons are recommended. Full article

(This article belongs to the Special Issue Quantum Gravity Phenomenology: Insights and Advances)

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23 pages, 713 KB

Open AccessArticle

Super-Accreting Active Galactic Nuclei as Neutrino Sources

by Gustavo E. Romero and Pablo Sotomayor

Universe 2025, 11(9), 288; https://doi.org/10.3390/universe11090288 - 25 Aug 2025

Viewed by 1045

Abstract

Active galactic nuclei (AGNs) often exhibit broad-line regions (BLRs), populated by high-velocity clouds in approximately Keplerian orbits around the central supermassive black hole (SMBH) at subparsec scales. During episodes of intense accretion at super-Eddington rates, the accretion disk can launch a powerful, radiation-driven [...] Read more.

Active galactic nuclei (AGNs) often exhibit broad-line regions (BLRs), populated by high-velocity clouds in approximately Keplerian orbits around the central supermassive black hole (SMBH) at subparsec scales. During episodes of intense accretion at super-Eddington rates, the accretion disk can launch a powerful, radiation-driven wind. This wind may overtake the BLR clouds, forming bowshocks around them. Two strong shocks arise: one propagating into the wind, and the other into the cloud. If the shocks are adiabatic, electrons and protons can be efficiently accelerated via a Fermi-type mechanism to relativistic energies. In sufficiently dense winds, the resulting high-energy photons are absorbed and reprocessed within the photosphere, while neutrinos produced in inelastic

p p

collisions escape. In this paper, we explore the potential of super-accreting AGNs as neutrino sources. We propose a new class of neutrino emitter: an AGN lacking jets and gamma-ray counterparts, but hosting a strong, opaque, disk-driven wind. As a case study, we consider a supermassive black hole with

M_{BH} = 10^{6} M_{⊙}

and accretion rates consistent with tidal disruption events (TDEs). We compute the relevant cooling processes for the relativistic particles under such conditions and show that super-Eddington accreting SMBHs can produce detectable neutrino fluxes with only weak electromagnetic counterparts. The neutrino flux may be observable by the next-generation IceCube Observatory (IceCube-Gen2) in nearby galaxies with a high BLR cloud filling factor. For galaxies hosting more massive black holes, detection is also possible with moderate filling factors if the source is sufficiently close, or at larger distances if the filling factor is high. Our model thus provides a new and plausible scenario for high-energy extragalactic neutrino sources, where both the flux and timescale of the emission are determined by the number of clouds orbiting the black hole and the duration of the super-accreting phase. Full article

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19 pages, 772 KB

Open AccessArticle

Earth-Lens Telescope for Distant Axion-like Particle Sources with Stimulated Backward Reflection

by Taiyo Nakamura and Kensuke Homma

Universe 2025, 11(9), 287; https://doi.org/10.3390/universe11090287 - 25 Aug 2025

Viewed by 232

Abstract

We propose a novel telescope concept based on Earth’s gravitational lensing effect, optimized for the detection of distant dark matter sources, particularly axion-like particles (ALPs). When a unidirectional flux of dark matter passes through Earth at sufficiently high velocity, gravitational lensing can concentrate [...] Read more.

We propose a novel telescope concept based on Earth’s gravitational lensing effect, optimized for the detection of distant dark matter sources, particularly axion-like particles (ALPs). When a unidirectional flux of dark matter passes through Earth at sufficiently high velocity, gravitational lensing can concentrate the flux at a distant focal region in space. Our method combines this lensing effect with stimulated backward reflection (SBR), arising from ALP decays that are induced by directing a coherent electromagnetic beam toward the focal point. The aim of this work is to numerically analyze the structure of the focal region and to develop a framework for estimating the sensitivity to ALP–photon coupling via this mechanism. Numerical calculations show that, assuming an average ALP velocity of 520 km/s—as suggested by the observed stellar stream S1—the focal region extends from

9 \times 10^{9}

m to

1.4 \times 10^{10}

m, with peak density near

9.6 \times 10^{9}

m. For a conservative point-like ALP source located approximately 8 kpc from the solar system, based on the S1 stream, the estimated sensitivity in the eV mass range reaches

g / M = O (10^{- 22}) {GeV}^{- 1}

. This concept thus opens a path toward a general-purpose, space-based ALP observatory that could, in principle, detect more distant sources—well beyond

O (10) kpc

—provided that ALP–photon coupling is sufficiently strong, that is,

M ≪ M_{Planck}

. Full article

(This article belongs to the Special Issue Origins and Natures of Inflation, Dark Matter and Dark Energy, 2nd Edition)

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27 pages, 9085 KB

Open AccessArticle

The History of Galaxy Mergers in IllustrisTNG

by Bendeguz Koncz, Istvan Horvath, András Péter Joó, Andreas Burkert and L. Viktor Tóth

Universe 2025, 11(9), 286; https://doi.org/10.3390/universe11090286 - 25 Aug 2025

Viewed by 471

Abstract

The process of galaxy evolution over cosmic time is not yet fully understood, since there is a debate on the impact of galaxy collisions on the star formation and metallicity. The local environment of the galaxy mergers could also have a large impact [...] Read more.

The process of galaxy evolution over cosmic time is not yet fully understood, since there is a debate on the impact of galaxy collisions on the star formation and metallicity. The local environment of the galaxy mergers could also have a large impact on the evolution of the galaxies, but it has not yet been possible to examine it in detail. Modern simulations with larger capacity, including the newest physical knowledge and new observations with JWST, help us to answer these questions. Using the IllustrisTNG cosmological simulation, we processed the catalogue data and the merger tree files of the TNG300-1 simulation. We calculated the galaxies’ average star formation rate (SFR) and mass at redshifts between 0 < z < 15. We investigated the environment of galaxy mergers, with the focus on the local density, and also examined how the SFR changes in merging galaxies. We compared our findings with JWST results and highlighted differences in the star formation rate density (SFRD) history between the models and observations. Full article

(This article belongs to the Special Issue Advances in Studies of Galaxies at High Redshift)

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20 pages, 4252 KB

Open AccessArticle

Spectral Analysis of Star-Forming Galaxies at z < 0.4 with FADO: Impact of Nebular Continuum on Galaxy Properties

by Yaosong Yu, Qihang Chen, Liang Jing, Ciro Pappalardo and Henrique Miranda

Universe 2025, 11(9), 285; https://doi.org/10.3390/universe11090285 - 24 Aug 2025

Viewed by 258

Abstract

The star formation rate (SFR) is a crucial astrophysical characteristic for understanding the formation and evolution of galaxies, determining the interplay between the interstellar medium and stellar activity. The mainstream approach to studying stellar properties in galaxies relies on stellar population synthesis models. [...] Read more.

The star formation rate (SFR) is a crucial astrophysical characteristic for understanding the formation and evolution of galaxies, determining the interplay between the interstellar medium and stellar activity. The mainstream approach to studying stellar properties in galaxies relies on stellar population synthesis models. However, these methods neglect nebular emission, which can bias SFR estimates. Recent studies have indicated that nebular emission is non-negligible in strongly star-forming regions. However, targeted research is currently limited, particularly regarding galaxies at slightly higher redshifts (

z < 0.4

). In this work, 696 star-formation galaxies with stellar mass in

10^{9} - 10^{11} M_{⊙}

are selected from the SDSS-DR18 and their spectra are fitted via the fitting analysis using differential evolution optimization (FADO) technique. FADO self-consistently fits both stellar and nebular emissions in galaxy spectra. The results show that the median

H_{α}

flux from FADO fitting differs from that of qsofitmore by approximately 0.028 dex. Considering the stellar mass effect, we found that although the nebular emission contribution (Nebular Ratio hereafter) is minimal, it increases modestly with redshift. We advocate explicitly accounting for nebular emission in the spectral fitting of higher-redshift galaxies, as its inclusion is essential to obtaining higher precision in future analyses. Full article

(This article belongs to the Section Galaxies and Clusters)

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28 pages, 439 KB

Open AccessArticle

Ball Lightning as a Profound Manifestation of Dark Matter Physics

by Ariel Zhitnitsky

Universe 2025, 11(9), 284; https://doi.org/10.3390/universe11090284 - 23 Aug 2025

Viewed by 207

Abstract

Ball lightning (BL) has been observed for centuries. There are a large number of books, review articles, and original scientific papers devoted to different aspects of the BL phenomenon. Yet, the basic features of this phenomenon have never been explained by known physics. [...] Read more.

Ball lightning (BL) has been observed for centuries. There are a large number of books, review articles, and original scientific papers devoted to different aspects of the BL phenomenon. Yet, the basic features of this phenomenon have never been explained by known physics. The main problem is the source which could power the dynamics of BL. We advocate the idea that dark matter (DM) in the form of axion quark nuggets (AQNs) made of standard model quarks and gluons (similar to the old idea of Witten’s strangelets) could internally generate the required power. The AQN model was invented long ago without any relation to BL physics. It was invented with a single motivation to explain the observed similarity,

Ω_{DM} \sim Ω_{visible}

, between visible and DM components. This relation represents a very generic feature of this framework, not sensitive to any parameters of the construction. However, with the same set of parameters being fixed long ago, this model is capable of addressing the key elements of the BL phenomenology, including the source of the energy powering the BL events. In particular, we argue that the visible size of BL, its typical life time, the frequency of its appearance, etc., are all consistent with the suggested proposal that BL represents a profound manifestation of DM physics represented by AQN objects. In this work, we limit ourselves to the analysis of the thunderstorm-related BL phenomena, though weather-unrelated BL events are also known to occur. We also formulate a number of specific possible tests which can refute or unambiguously substantiate this unorthodox proposal on the nature of BL. Full article

(This article belongs to the Special Issue Tensions, Anomalies, and Challenges in the Standard Cosmological Model)

21 pages, 778 KB

Open AccessArticle

Dynamical Systems Analysis of Timelike Geodesics in a Lorentz-Violating Black Hole Spacetime

by Aqeela Razzaq, Jianwen Liu and Fabao Gao

Universe 2025, 11(9), 283; https://doi.org/10.3390/universe11090283 - 23 Aug 2025

Viewed by 223

Abstract

This paper investigates the global dynamics of timelike geodesics of a spherically symmetric black hole under Lorentz-violating effects governed by parameters

λ

(scaling exponent) and

Υ

(Lorentz violation strength). By employing dynamical system techniques, including Poincaré compactification and blow-up methods, we systematically explore [...] Read more.

This paper investigates the global dynamics of timelike geodesics of a spherically symmetric black hole under Lorentz-violating effects governed by parameters

λ

(scaling exponent) and

Υ

(Lorentz violation strength). By employing dynamical system techniques, including Poincaré compactification and blow-up methods, we systematically explore finite and infinite equilibrium states of the system derived from a black hole solution with power-law corrections to the Schwarzschild metric. For varying

λ

(ranging from −2 to 2) and fixed

Υ

values, we classify the nature of equilibrium states (saddle, center, and node) and analyze their stability. Key findings reveal that the number of equilibrium states increases as

λ

decreases: two states for

λ = 2

, three for

λ = 1

, four for

λ = 2 / 3

, and additional configurations for

λ = - 2

. The phase plane diagrams and global dynamics demonstrate distinct topological structures, including attractors at infinity and multi-horizon black hole solutions. Furthermore, degenerate equilibrium states at infinity are resolved through directional blow-ups, elucidating their non-hyperbolic behavior. This study highlights the critical role of Lorentz-violating parameters in shaping the stability and long-term evolution of timelike geodesics, offering new insights into modified black hole physics and spacetime dynamics. Full article

(This article belongs to the Section Cosmology)

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10 pages, 1909 KB

Open AccessArticle

Research on Removing Thin Cloud Interference in Solar Flare Monitoring with SMAT-Configured Telescopes

by Hongyan Li, Shangbin Yang, Xing Hu and Haiqing Xu

Universe 2025, 11(9), 282; https://doi.org/10.3390/universe11090282 - 22 Aug 2025

Viewed by 215

Abstract

The precise monitoring of solar flares holds significant scientific value for space mission safety, communication security, and space environment forecasting. The H

α

line has long been utilized as a tool to extract information about the structure and dynamics of the solar chromosphere [...] Read more.

The precise monitoring of solar flares holds significant scientific value for space mission safety, communication security, and space environment forecasting. The H

α

line has long been utilized as a tool to extract information about the structure and dynamics of the solar chromosphere and is crucial for observing solar activities such as prominences and flares. However, ground-based H

α

observations are susceptible to cloud interference, which significantly reduces data reliability and complicates the effective separation of genuine flare signals from cloud modulation effects. To address this challenge, our study proposes a dual-band brightness ratio method tailored to the SMAT configuration, leveraging synchronous observation data from the Huairou SMAT at two wavelengths (photospheric 5324 Å and chromospheric 6562.8 Å). Observational data validation demonstrates that this method can effectively characterize true chromospheric brightness variations. In real observational data, the reconstructed brightness curve successfully recovered the brightness peak of an M1.5 class flare, with the peak position aligning well with the X-ray flux peak. This method enhances the accuracy of flare monitoring under cloudy conditions for SMAT, providing a promising pathway for high-reliability ground-based solar activity observations with this telescope. Full article

(This article belongs to the Section Solar and Stellar Physics)

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11 pages, 268 KB

Open AccessArticle

Neutron Reflectometry and Short-Range Modifications of Gravity

by Jesriel Matias Rocha and Fábio Dahia

Universe 2025, 11(9), 281; https://doi.org/10.3390/universe11090281 - 22 Aug 2025

Viewed by 261

Abstract

Using the precise measurements of the scattering length of neutron–matter interaction obtained through the method of neutron reflectometry by gravity, we establish new empirical constraints on deviations from the standard behavior of the gravitational interaction at short distances predicted by large extra-dimensional models. [...] Read more.

Using the precise measurements of the scattering length of neutron–matter interaction obtained through the method of neutron reflectometry by gravity, we establish new empirical constraints on deviations from the standard behavior of the gravitational interaction at short distances predicted by large extra-dimensional models. We compute explicitly, in the thick-brane scenario, the corrections to the neutron–nucleus scattering length arising from the influence of hidden dimensions. The experimental data allow us to place empirical bounds on the free parameters of the extra-dimensional model, expressed as a function of the nuclear scattering length. Full article

(This article belongs to the Special Issue Exploring and Constraining Alternative Theories of Gravity)

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Universe, Volume 11, Issue 9 (September 2025) – 22 articles

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