Congratulations to Prof. Roger Penrose, Advisory Board member of Universe, for receiving the Nobel Prize in Physics 2020.
Journal Description
Universe
Universe
is a peer-reviewed open access journal focused on principles and new discoveries in the universe. Universe is published monthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, SCIE (Web of Science), Astrophysics Data System, INSPIRE, CAPlus / SciFinder, Inspec, and other databases.
- Journal Rank: JCR - Q2 (Astronomy & Astrophysics) / CiteScore - Q2 (General Physics and Astronomy)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 20.6 days after submission; acceptance to publication is undertaken in 2.9 days (median values for papers published in this journal in the second half of 2023).
- 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.
- Companion journal: Astronomy.
Impact Factor:
2.9 (2022);
5-Year Impact Factor:
2.4 (2022)
Latest Articles
Phantom Scalar Field Cosmologies Constrained by Early Cosmic Measurements
Universe 2024, 10(6), 232; https://doi.org/10.3390/universe10060232 - 23 May 2024
Abstract
In this work, we explore new constraints on phantom scalar field cosmologies with a scalar field employing early-time catalogs related to CMB measurements, along with the local standard observables, like Supernovae Type Ia (SNIa), measurements (Cosmick clocks), and Baryon
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In this work, we explore new constraints on phantom scalar field cosmologies with a scalar field employing early-time catalogs related to CMB measurements, along with the local standard observables, like Supernovae Type Ia (SNIa), measurements (Cosmick clocks), and Baryon Acoustic Oscillation (BAO) baselines. In particular, we studied a tracker phantom field with hyperbolic polar coordinates that have been proposed in the literature. The main goal is to obtain precise cosmological constraints for and , in comparison to other constructions that present tension in early cosmological parameters. Our results show that phantom scalar field cosmologies have a reduced statistical tension on that it is less than 3 using model-independent CMB catalogs as SPT-3G+WMAP9 and ACTPol DR-4+WMAP9 baselines. This suggests that these models, using a different phantom potential, might address the Hubble constant problem and reduce the systematics involved.
Full article
(This article belongs to the Special Issue The Nature of Dark Energy)
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Open AccessReview
Magnetar QPOs and Neutron Star Crust Elasticity
by
Hajime Sotani
Universe 2024, 10(6), 231; https://doi.org/10.3390/universe10060231 - 22 May 2024
Abstract
The crust region is a tiny fraction of neutron stars, but it has a variety of physical properties and plays an important role in astronomical observations. One of the properties characterizing the crust is elasticity. In this review, with the approach of asteroseismology,
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The crust region is a tiny fraction of neutron stars, but it has a variety of physical properties and plays an important role in astronomical observations. One of the properties characterizing the crust is elasticity. In this review, with the approach of asteroseismology, we systematically examine neutron star oscillations excited by crust elasticity, adopting the Cowling approximation. In particular, by identifying the quasi-periodic oscillations observed in magnetar flares with the torsional oscillations, we make a constraint on the nuclear saturation parameters. In addition, we also discuss how the shear and interface modes depend on the neutron star properties. Once one detects an additional signal associated with neutron star oscillations, one can obtain a more severe constraint on the saturation parameters and/or neutron star properties, which must be a qualitatively different constraint obtained from terrestrial experiments and help us to complementarily understand astrophysics and nuclear physics.
Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)
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Open AccessArticle
Improved Galaxy Morphology Classification with Convolutional Neural Networks
by
Raul Urechiatu and Marc Frincu
Universe 2024, 10(6), 230; https://doi.org/10.3390/universe10060230 - 21 May 2024
Abstract
The increased volume of images and galaxies surveyed by recent and upcoming projects consolidates the need for accurate and scalable automated AI-driven classification methods. This paper proposes a new algorithm based on a custom neural network architecture for classifying galaxies from deep space
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The increased volume of images and galaxies surveyed by recent and upcoming projects consolidates the need for accurate and scalable automated AI-driven classification methods. This paper proposes a new algorithm based on a custom neural network architecture for classifying galaxies from deep space surveys. The convolutional neural network (CNN) presented is trained using 10,000 galaxy images obtained from the Galaxy Zoo 2 dataset. It is designed to categorize galaxies into five distinct classes: completely round smooth, in-between smooth (falling between completely round and cigar-shaped), cigar-shaped smooth, edge-on, and spiral. The performance of the proposed CNN is assessed using a set of metrics such as accuracy, precision, recall, F1 score, and area under the curve. We compare our solution with well-known architectures like ResNet-50, DenseNet, EfficientNet, Inception, MobileNet, and one proposed model for galaxy classification found in the recent literature. The results show an accuracy rate of 96.83%, outperforming existing algorithms.
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(This article belongs to the Section Galaxies and Clusters)
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Open AccessArticle
The Parallel Compact Object CALculator: An Efficient General Relativistic Initial Data Solver for Compact Objects
by
Lambros Boukas, Antonios Tsokaros and Kōji Uryū
Universe 2024, 10(5), 229; https://doi.org/10.3390/universe10050229 - 20 May 2024
Abstract
Every numerical general relativistic investigation starts from the solution of the initial value equations at a given time. Astrophysically relevant initial values for different systems lead to distinct sets of equations that obey specific assumptions tied to the particular problem. Therefore, a robust
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Every numerical general relativistic investigation starts from the solution of the initial value equations at a given time. Astrophysically relevant initial values for different systems lead to distinct sets of equations that obey specific assumptions tied to the particular problem. Therefore, a robust and efficient solver for a variety of strongly gravitating sources is needed. In this work, we present the OpenMP version of the Compact Object CALculator (COCAL) on shared memory processors. We performed extensive profiling of the core COCAL modules in order to identify bottlenecks in efficiency, which we addressed. Using modest resources, the new parallel code achieves speedups of approximately one order of magnitude relative to the original serial COCAL code, which is crucial for parameter studies of computationally expensive systems such as magnetized neutron stars, as well as its further development towards more realistic scenarios. As a novel example of our new code, we compute a binary quark system where each companion has a dimensionless spin of aligned with the orbital angular momentum.
Full article
(This article belongs to the Special Issue Exploring Quark Matter under Extreme Scenarios of Temperature and Density)
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Open AccessReview
Detectors and Shieldings: Past and Future at LUNA
by
Chemseddine Ananna, Lucia Barbieri, Axel Boeltzig, Matteo Campostrini, Fausto Casaburo, Alessandro Compagnucci, Laszlo Csedreki, Riccardo Maria Gesue, Jordan Marsh, Daniela Mercogliano, Denise Piatti, Duncan Robb, Ragandeep Singh Sidhu and Jakub Skowronski
Universe 2024, 10(5), 228; https://doi.org/10.3390/universe10050228 - 20 May 2024
Abstract
Nuclear reactions are responsible for the chemical evolution of stars, galaxies and the Universe. Unfortunately, at temperatures of interest for nuclear astrophysics, the cross-sections of the thermonuclear reactions are in the pico- femto-barn range and thus measuring them in the laboratory is extremely
[...] Read more.
Nuclear reactions are responsible for the chemical evolution of stars, galaxies and the Universe. Unfortunately, at temperatures of interest for nuclear astrophysics, the cross-sections of the thermonuclear reactions are in the pico- femto-barn range and thus measuring them in the laboratory is extremely challenging. In this framework, major steps forward were made with the advent of underground nuclear astrophysics, pioneered by the Laboratory for Underground Nuclear Astrophysics (LUNA). The cosmic background reduction by several orders of magnitude obtained at LUNA, however, needs to be combined with high-performance detectors and dedicated shieldings to obtain the required sensitivity. In the present paper, we report on the recent and future detector-shielding designs at LUNA.
Full article
(This article belongs to the Special Issue Recent Outcomes and Future Challenges in Nuclear Astrophysics)
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Open AccessArticle
Uncovering the First AGN Jets with AXIS
by
Thomas Connor, Eduardo Bañados, Nico Cappelluti and Adi Foord
Universe 2024, 10(5), 227; https://doi.org/10.3390/universe10050227 - 18 May 2024
Abstract
Jets powered by AGN in the early Universe ( ) have the potential to not only define the evolutionary trajectories of the first-forming massive galaxies but to enable the accelerated growth of their associated SMBHs. Under typical assumptions, jets could
[...] Read more.
Jets powered by AGN in the early Universe ( ) have the potential to not only define the evolutionary trajectories of the first-forming massive galaxies but to enable the accelerated growth of their associated SMBHs. Under typical assumptions, jets could even rectify observed quasars with light seed formation scenarios; however, not only are constraints on the parameters of the first jets lacking, observations of these objects are scarce. Owing to the significant energy density of the CMB at these epochs capable of quenching radio emission, observations will require powerful, high angular resolution X-ray imaging to map and characterize these jets. As such, AXIS will be necessary to understand early SMBH growth and feedback. This White Paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS White Papers can be found at the AXIS website.
Full article
(This article belongs to the Section Galaxies and Clusters)
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Open AccessArticle
Nuclear Matter Equation of State in the Brueckner–Hartree–Fock Approach and Standard Skyrme Energy Density Functionals
by
Isaac Vidaña, Jérôme Margueron and Hans-Josef Schulze
Universe 2024, 10(5), 226; https://doi.org/10.3390/universe10050226 - 17 May 2024
Abstract
The equation of state of asymmetric nuclear matter as well as the neutron and proton effective masses and their partial-wave and spin–isospin decomposition are analyzed within the Brueckner–Hartree–Fock approach. Theoretical uncertainties for all these quantities are estimated by using several phase-shift-equivalent nucleon–nucleon forces
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The equation of state of asymmetric nuclear matter as well as the neutron and proton effective masses and their partial-wave and spin–isospin decomposition are analyzed within the Brueckner–Hartree–Fock approach. Theoretical uncertainties for all these quantities are estimated by using several phase-shift-equivalent nucleon–nucleon forces together with two types of three-nucleon forces, phenomenological and microscopic. It is shown that the choice of the three-nucleon force plays an important role above saturation density, leading to different density dependencies of the energy per particle. These results are compared to the standard form of the Skyrme energy density functional, and we find that it is not possible to reproduce the BHF predictions in the channels in symmetric and neutron matter above saturation density, already at the level of the two-body interaction, and even more including the three-body interaction.
Full article
(This article belongs to the Special Issue Studies in Neutron Stars)
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Open AccessCommunication
Detecting Wandering Intermediate-Mass Black Holes with AXIS in the Milky Way and Local Massive Galaxies
by
Fabio Pacucci, Bryan Seepaul, Yueying Ni, Nico Cappelluti and Adi Foord
Universe 2024, 10(5), 225; https://doi.org/10.3390/universe10050225 - 17 May 2024
Abstract
This white paper explores the detectability of intermediate-mass black holes (IMBHs) wandering in the Milky Way (MW) and massive local galaxies, with a particular emphasis on the role of AXIS. IMBHs, ranging within , are commonly found
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This white paper explores the detectability of intermediate-mass black holes (IMBHs) wandering in the Milky Way (MW) and massive local galaxies, with a particular emphasis on the role of AXIS. IMBHs, ranging within , are commonly found at the centers of dwarf galaxies and may exist, yet undiscovered, in the MW. By using model spectra for advection-dominated accretion flows (ADAFs), we calculated the expected fluxes emitted by a population of wandering IMBHs with masses of in various MW environments and extrapolated our results to massive local galaxies. Around of the potential population of wandering IMBHs in the MW can be detected in an AXIS deep field. We proposed criteria to aid with selecting IMBH candidates using already available optical surveys. We also showed that IMBHs wandering in >200 galaxies within 10 Mpc can be easily detected with AXIS when passing within dense galactic environments (e.g., molecular clouds and cold neutral medium). In summary, we highlighted the potential X-ray detectability of wandering IMBHs in local galaxies and provided insights for guiding future surveys. Detecting wandering IMBHs is crucial for understanding their demographics and evolution and the merging history of galaxies. This white paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS white papers can be found at the AXIS website.
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(This article belongs to the Section Galaxies and Clusters)
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Open AccessCommunication
Gravitational Waves of Holographic QCD Phase Transition with Hyperscaling Violation
by
Zhourun Zhu, Manman Sun, Rui Zhou, Jinzhong Han and Defu Hou
Universe 2024, 10(5), 224; https://doi.org/10.3390/universe10050224 - 17 May 2024
Abstract
In this paper, we study the gravitational waves of holographic QCD phase transition with hyperscaling violation. We consider an Einstein–Maxwell Dilaton background and discuss the confinement–deconfinement phase transition between thermally charged AdS and AdS black holes. We find that hyperscaling violation reduces the
[...] Read more.
In this paper, we study the gravitational waves of holographic QCD phase transition with hyperscaling violation. We consider an Einstein–Maxwell Dilaton background and discuss the confinement–deconfinement phase transition between thermally charged AdS and AdS black holes. We find that hyperscaling violation reduces the phase transition temperature. In a further study, we discuss the effect of hyperscaling violation on the GW spectrum. We found that the hyperscaling violation exponent suppresses the peak frequency of the total GW spectrum. Moreover, the results of the GW spectrum may be detected by IPTA, SKA, BBO, and NANOGrav. We also find that the hyperscaling violation exponent suppresses the peak frequency of the bubble-collision spectrum . Hyperscaling violation enhances the energy densities of the sound wave spectrum and the MHD turbulence spectrum . The total GW spectrum is dominated by the contribution of the bubble collision in runaway bubbles case.
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(This article belongs to the Special Issue Holographic Principle in Universe)
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Open AccessArticle
The Rotation of Classical Bulges in Barred Galaxies in the Presence of Gas
by
Rubens E. G. Machado, Kenzo R. Sakamoto, Andressa Wille and Gustavo F. Gonçalves
Universe 2024, 10(5), 223; https://doi.org/10.3390/universe10050223 - 16 May 2024
Abstract
Barred galaxies often develop a box/peanut pseudobulge, but they can also host a nearly spherical classical bulge, which is known to gain rotation due to the bar. We aim to explore how the presence of gas impacts the rotation of classical bulges. We
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Barred galaxies often develop a box/peanut pseudobulge, but they can also host a nearly spherical classical bulge, which is known to gain rotation due to the bar. We aim to explore how the presence of gas impacts the rotation of classical bulges. We carried out a comprehensive set of hydrodynamical N-body simulations with different combinations of bulge masses and gas fractions. In these models, both massive bulges and high gas content tend to inhibit the formation of strong bars. For low-mass bulges, the resulting bar is stronger in cases of low gas content. In the stronger bar models, bulges acquire more angular momentum and thus display considerable rotational velocity. Such bulges also develop anisotropic velocity dispersions and become triaxial in shape. We found that the rotation of the bulge becomes less pronounced as the gas fraction is increased from 0 to 30%. These results indicate that the gas content has a significant effect on the dynamics of the classical bulge, because it influences bar strength. Particularly in the case of the low-mass bulges (10% bulge mass fraction), all of the measured rotational and structural properties of the classical bulge depend strongly and systematically on the gas content of the galaxy.
Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")
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Open AccessArticle
Positive-Energy Dirac Particles and Dark Matter
by
Eugene Bogomolny
Universe 2024, 10(5), 222; https://doi.org/10.3390/universe10050222 - 16 May 2024
Abstract
The relativistic positive-energy wave equation proposed by P. Dirac in 1971 is an old but largely forgotten subject. The purpose of this note is to speculate that particles described by this equation (called here Dirac particles) are natural candidates for the dark matter.
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The relativistic positive-energy wave equation proposed by P. Dirac in 1971 is an old but largely forgotten subject. The purpose of this note is to speculate that particles described by this equation (called here Dirac particles) are natural candidates for the dark matter. The reasoning is based on a fact that the internal structure of such particles simply prohibits their interaction with electromagnetic fields (at least with the minimal coupling) which is exactly what is required for dark matter. Dirac particles have quite unusual properties. In particular, they are transformed by an infinite-dimensional representation of the homogeneous Lorentz group, which clearly distinguishes them from all known elementary particles described by finite-dimensional representations and hints to a physics beyond the Standard Model. To clarify the topic, a brief review of the main features of the above-mentioned Dirac equation is given.
Full article
(This article belongs to the Section Cosmology)
Open AccessReview
Future Long-Baseline Neutrino Experiments
by
Francesco Terranova
Universe 2024, 10(5), 221; https://doi.org/10.3390/universe10050221 - 16 May 2024
Abstract
Long-baseline neutrino experiments represent the optimal platforms for probing the lepton Yukawa sector of the Standard Model, and significant experiments are either under construction or in the planning stages. This review delves into the scientific motivations behind these facilities, which stem from the
[...] Read more.
Long-baseline neutrino experiments represent the optimal platforms for probing the lepton Yukawa sector of the Standard Model, and significant experiments are either under construction or in the planning stages. This review delves into the scientific motivations behind these facilities, which stem from the pivotal 2012 discovery of the mixing angle. We provide an overview of the two ongoing projects, DUNE and HyperKamiokande, detailing their physics potential and the technical hurdles they face. Furthermore, we briefly examine proposals for forthcoming endeavors and innovative concepts that could push beyond conventional Superbeam technology.
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(This article belongs to the Special Issue Neutrinos from Artificial Sources)
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Open AccessArticle
Estimating the Mass of Galactic Components Using Machine Learning Algorithms
by
Jessica N. López-Sánchez, Erick Munive-Villa, Ana A. Avilez-López and Oscar M. Martínez-Bravo
Universe 2024, 10(5), 220; https://doi.org/10.3390/universe10050220 - 15 May 2024
Abstract
The estimation of galactic component masses can be carried out through various approaches that involve a host of assumptions about baryon dynamics or the dark matter model. In contrast, this work introduces an alternative method for predicting the masses of the disk, bulge,
[...] Read more.
The estimation of galactic component masses can be carried out through various approaches that involve a host of assumptions about baryon dynamics or the dark matter model. In contrast, this work introduces an alternative method for predicting the masses of the disk, bulge, stellar, and total mass using the k-nearest neighbours, linear regression, random forest, and neural network (NN) algorithms, reducing the dependence on any particular hypothesis. The ugriz photometric system was selected as the set of input features, and the training was performed using spiral galaxies in Guo’s mock catalogue from the Millennium simulation. In general, all of the algorithms provide good predictions for the galaxy’s mass from to , corresponding to the central region of the training domain. The NN algorithm showed the best performance. To validate the algorithm, we used the SDSS survey and found that the predictions of disk-dominant galaxies’ masses lie within a confidence level, while galaxies with larger bulges are predicted at a confidence level. The NN also reveals scaling relations between mass components and magnitudes. However, predictions for less luminous galaxies are biased due to observational limitations. Our study demonstrates the efficacy of these methods with the potential for further enhancement through the addition of observational data or galactic dynamics.
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(This article belongs to the Section Galaxies and Clusters)
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Open AccessArticle
Orbital Stability Study of the Taiji Space Gravitational Wave Detector
by
Yu-Yang Zhang, Geng Li and Bo Wen
Universe 2024, 10(5), 219; https://doi.org/10.3390/universe10050219 - 15 May 2024
Abstract
Space-based gravitational wave detection is extremely sensitive to disturbances. The Keplerian configuration cannot accurately reflect the variations in spacecraft configuration. Planetary gravitational disturbances are one of the main sources. Numerical simulation is an effective method to investigate the impact of perturbation on spacecraft
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Space-based gravitational wave detection is extremely sensitive to disturbances. The Keplerian configuration cannot accurately reflect the variations in spacecraft configuration. Planetary gravitational disturbances are one of the main sources. Numerical simulation is an effective method to investigate the impact of perturbation on spacecraft orbits. This study shows that, in the context of the Taiji project, Earth’s gravity is an essential factor in the change in heliocentric formation configuration, contributing to the relative acceleration between spacecrafts in the order of · . Considering 00:00:00 on 27 October 2032 as the initial orbiting moment, under the influence of Earth’s gravitational perturbation, the maximum relative change in armlengths and variation rates of armlengths for Taiji is , · , respectively, compared with the unperturbed Keplerian orbit. Additionally, by considering the gravitational perturbations of Venus and Jupiter, the armlength and relative velocity for Taiji are reduced by and , respectively, compared with when only considering that of Earth. The maximum amplitude of the formation motion indicator changes with the orbit entry time. Results show that the relative velocity increase between the spacecrafts is minimal when the initial orbital moment occurs in July. Moreover, the numerical simulation results are inconsistent when using different ephemerides. The differences between ephemerides DE440 and DE430 are smaller than those between DE440 and DE421.
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(This article belongs to the Section Gravitation)
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Open AccessArticle
Hourglass Magnetic Field of a Protostellar System
by
Shantanu Basu, Xiyuan Li and Gianfranco Bino
Universe 2024, 10(5), 218; https://doi.org/10.3390/universe10050218 - 15 May 2024
Abstract
An hourglass-shaped magnetic field pattern arises naturally from the gravitational collapse of a star-forming gas cloud. Most studies have focused on the prestellar collapse phase, when the structure has a smooth and monotonic radial profile. However, most observations target dense clouds that already
[...] Read more.
An hourglass-shaped magnetic field pattern arises naturally from the gravitational collapse of a star-forming gas cloud. Most studies have focused on the prestellar collapse phase, when the structure has a smooth and monotonic radial profile. However, most observations target dense clouds that already contain a central protostar, and possibly a circumstellar disk. We utilize an analytic treatment of the magnetic field along with insights gained from simulations to develop a more realistic magnetic field model for the protostellar phase. Key elements of the model are a strong radial magnetic field in the region of rapid collapse, an off-center peak in the magnetic field strength (a consequence of magnetic field dissipation in the circumstellar disk), and a strong toroidal field that is generated in the region of rapid collapse and outflow generation. A model with a highly pinched and twisted magnetic field pattern in the inner collapse zone facilitates the interpretation of magnetic field patterns observed in protostellar clouds.
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(This article belongs to the Special Issue Advances in Star Formation in the Milky Way)
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Open AccessArticle
Bose and Fermi Gases in Metric-Affine Gravity and Linear Generalized Uncertainty Principle
by
Aneta Wojnar and Débora Aguiar Gomes
Universe 2024, 10(5), 217; https://doi.org/10.3390/universe10050217 - 14 May 2024
Abstract
Palatini-like theories of gravity have a remarkable connection to models incorporating linear generalized uncertainty principles. Considering this, we delve into the thermodynamics of systems comprising both Bose and Fermi gases. Our analysis encompasses the equations of state for various systems, including general Fermi
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Palatini-like theories of gravity have a remarkable connection to models incorporating linear generalized uncertainty principles. Considering this, we delve into the thermodynamics of systems comprising both Bose and Fermi gases. Our analysis encompasses the equations of state for various systems, including general Fermi gases, degenerate Fermi gases, Boltzmann gases, and Bose gases such as phonons and photons, as well as Bose–Einstein condensates and liquid helium.
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(This article belongs to the Collection Modified Theories of Gravity and Cosmological Applications)
Open AccessArticle
‘X-Currents’ and Extreme Brightening in Dayside Aurora
by
Gerard Fasel, Abrielle Wang, Audrey Daucher, Lou-Chuang Lee, Julia Pepperdine, Owen Bradley, John Mann, Minji Kim, Benjamin Swonger, Fred Sigernes and Dag Lorentzen
Universe 2024, 10(5), 216; https://doi.org/10.3390/universe10050216 - 14 May 2024
Abstract
Solar-terrestrial interaction is a dynamic process that manifests itself in the ionosphere. Interplanetary (IP) shocks or solar wind dynamic pressure pulses can generate enhanced brightening in dayside aurora. Foreshock transients are capable of inducing pressure changes, larger in magnitude than solar wind pressure
[...] Read more.
Solar-terrestrial interaction is a dynamic process that manifests itself in the ionosphere. Interplanetary (IP) shocks or solar wind dynamic pressure pulses can generate enhanced brightening in dayside aurora. Foreshock transients are capable of inducing pressure changes, larger in magnitude than solar wind pressure pulses, which also contribute to intensifying dayside aurora. These pressure variations can accelerate particles into the ionosphere, generating field-aligned currents that produce magnetic impulse events and enhanced dayside auroral activity with periods of increased brightening. This study presents several dayside auroral brightening events that are not associated with IP shocks or solar wind dynamic pressure pulses. The dayside auroral brightening events are associated with a green (557.7 nm) to red (630.0 nm) ratio which is greater than 15. These extreme brightening events (EBEs) begin on the eastern or western end of a pre-existing dayside auroral arc. Periodic pulses of enhanced brightening are correlated with large sharp increases in the X-component (points toward the north-geographic pole) from ground magnetometers in the IMAGE network. EBEs occur predominately before magnetic noon and with X-component signatures from high-latitude stations. Ground-based data were obtained from the Kjell Henriksen Observatory in Longyearbyen and the IMAGE magnetometer network.
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(This article belongs to the Section Planetary Sciences)
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Open AccessArticle
BRDF-Based Photometric Modeling of LEO Constellation Satellite from Massive Observations
by
Yao Lu
Universe 2024, 10(5), 215; https://doi.org/10.3390/universe10050215 - 14 May 2024
Abstract
Modeling the brightness of satellites in large Low-Earth Orbit (LEO) constellations can not only assist the astronomical community in assessing the impact of reflected light from satellites, optimizing observing schedules and guiding data processing, but also motivate satellite operators to improve their satellite
[...] Read more.
Modeling the brightness of satellites in large Low-Earth Orbit (LEO) constellations can not only assist the astronomical community in assessing the impact of reflected light from satellites, optimizing observing schedules and guiding data processing, but also motivate satellite operators to improve their satellite designs, thus facilitating cooperation and consensus among different stakeholders. This work presents a photometric model of the Starlink satellites based on the Bidirectional Reflectance Distribution Function (BRDF) using millions of photometric observations. To enhance model accuracy and computational efficiency, data filtering and reduction are employed, and chassis blocking on the solar array and the earthshine effect are taken into account. The assumptions of the model are also validated by showing that the satellite attitude is as expected, the solar array is nearly perpendicular to the chassis, and both the solar array pseudo-specular reflection and the chassis earthshine should be included in the model. The reflectance characteristics of the satellites and the apparent magnitude distributions over station are finally discussed based on the photometric predictions from the model. In addition to assessing the light pollution and guiding the development of response measures, accurate photometric models of satellites can also play an important role in areas such as space situational awareness.
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(This article belongs to the Section Stellar Astronomy)
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Open AccessArticle
Stellar Classification with Vision Transformer and SDSS Photometric Images
by
Yi Yang and Xin Li
Universe 2024, 10(5), 214; https://doi.org/10.3390/universe10050214 - 13 May 2024
Abstract
With the development of large-scale sky surveys, an increasing number of stellar photometric images have been obtained. However, most stars lack spectroscopic data, which hinders stellar classification. Vision Transformer (ViT) has shown superior performance in image classification tasks compared to most convolutional neural
[...] Read more.
With the development of large-scale sky surveys, an increasing number of stellar photometric images have been obtained. However, most stars lack spectroscopic data, which hinders stellar classification. Vision Transformer (ViT) has shown superior performance in image classification tasks compared to most convolutional neural networks (CNNs). In this study, we propose an stellar classification network based on the Transformer architecture, named stellar-ViT, aiming to efficiently and accurately classify the spectral class for stars when provided with photometric images. By utilizing RGB images synthesized from photometric data provided by the Sloan Digital Sky Survey (SDSS), our model can distinguish the seven main stellar categories: O, B, A, F, G, K, and M. Particularly, our stellar-ViT-gri model, which reaches an accuracy of 0.839, outperforms traditional CNNs and the current state-of-the-art stellar classification network SCNet when processing RGB images synthesized from the gri bands. Furthermore, with the introduction of urz band data, the overall accuracy of the stellar-ViT model reaches 0.863, further demonstrating the importance of additional band information in improving classification performance. Our approach showcases the effectiveness and feasibility of using photometric images and Transformers for stellar classification through simple data augmentation strategies and robustness analysis of training dataset sizes. The stellar-ViT model maintains good performance even in small sample scenarios, and the inclusion of urz band data reduces the likelihood of misclassifying samples as lower-temperature subtypes.
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(This article belongs to the Section Astroinformatics and Astrostatistics)
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Open AccessEditorial
Editorial to the Special Issue: “Recent Advances in Gamma Ray Astrophysics and Future Perspectives”
by
Patrizia Romano
Universe 2024, 10(5), 213; https://doi.org/10.3390/universe10050213 - 10 May 2024
Abstract
This Special Issue is a collection of reviews highlighting the recent progress in the very vast and closely related fields of -ray astrophysics and astro-particle physics in recent years, looking toward a very promising future [...]
Full article
(This article belongs to the Special Issue Recent Advances in Gamma Ray Astrophysics and Future Perspectives)
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Conferences
Special Issues
Special Issue in
Universe
Blazar Bursts: Theory and Observation
Guest Editor: Yunguo JiangDeadline: 31 May 2024
Special Issue in
Universe
Small-Scale Eruptions on the Sun
Guest Editors: Robertus Erdelyi, Jie Chen, Yuandeng Shen, Marianna KorsosDeadline: 30 June 2024
Special Issue in
Universe
Advanced Studies in Ultra-High-Energy Cosmic Rays
Guest Editors: Gina Isar, François MontanetDeadline: 30 July 2024
Special Issue in
Universe
A Multimessenger View of Supermassive Black Holes and the Quasar Main Sequence
Guest Editors: Ascension Del Olmo, Paola MarzianiDeadline: 31 August 2024
Topical Collections
Topical Collection in
Universe
New Results on Galaxy Evolution from the James Webb Space Telescope
Collection Editor: Guinevere Kauffmann
Topical Collection in
Universe
Modified Theories of Gravity and Cosmological Applications
Collection Editors: Panayiotis Stavrinos, Emmanuel N. Saridakis
Topical Collection in
Universe
Open Questions in Black Hole Physics
Collection Editors: Gonzalo Olmo, Diego Rubiera-Garcia
Topical Collection in
Universe
Nobel Prize 2020: Selected Articles on Black Hole and General Relativity
Collection Editor: Lorenzo Iorio