Universe

26 pages, 1105 KiB

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

Viewed by 928

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 [...] Read more.

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

0.43

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)

► Show Figures

Figure 1

19 pages, 12433 KiB

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

Viewed by 1051

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)

► Show Figures

Figure 1

9 pages, 843 KiB

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

Cited by 4 | Viewed by 781

Abstract

Jets powered by AGN in the early Universe (

z ≳ 6

) 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 (

z ≳ 6

) 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)

► Show Figures

Figure 1

20 pages, 591 KiB

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

Cited by 1 | Viewed by 930

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 [...] Read more.

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

(S, T)

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)

► Show Figures

Figure 1

7 pages, 1120 KiB

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

Cited by 3 | Viewed by 988

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

10^{3 - 6} M_{⊙}

, are commonly found [...] Read more.

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

10^{3 - 6} M_{⊙}

, 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

10^{5} M_{⊙}

in various MW environments and extrapolated our results to massive local galaxies. Around

40 %

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. Full article

(This article belongs to the Section Galaxies and Clusters)

► Show Figures

Figure 1

10 pages, 366 KiB

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

Viewed by 931

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

h^{2} Ω_{e n v}

. Hyperscaling violation enhances the energy densities of the sound wave spectrum

h^{2} Ω_{s w}

and the MHD turbulence spectrum

h^{2} Ω_{t u r b}

. The total GW spectrum is dominated by the contribution of the bubble collision in runaway bubbles case. Full article

(This article belongs to the Special Issue Holographic Principle in Universe)

► Show Figures

Figure 1

25 pages, 2077 KiB

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

Cited by 1 | Viewed by 985

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 [...] Read more.

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")

► Show Figures

Figure 1

15 pages, 310 KiB

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

Cited by 5 | Viewed by 981

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. [...] Read more.

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)

17 pages, 1256 KiB

Open AccessReview

Future Long-Baseline Neutrino Experiments

by Francesco Terranova

Universe 2024, 10(5), 221; https://doi.org/10.3390/universe10050221 - 16 May 2024

Cited by 1 | Viewed by 1037

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

θ_{13}

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. Full article

(This article belongs to the Special Issue Neutrinos from Artificial Sources)

► Show Figures

Figure 1

15 pages, 2535 KiB

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

Viewed by 1111

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

10^{9} M_{⊙}

to

10^{11} M_{⊙}

, 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

99 %

confidence level, while galaxies with larger bulges are predicted at a

95 %

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. Full article

(This article belongs to the Section Galaxies and Clusters)

► Show Figures

Figure 1

15 pages, 8887 KiB

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

Viewed by 851

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 [...] Read more.

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

O (10^{- 6}) m

·

s^{- 2}

. 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

1.6 \times 10^{5} km

,

32 m

·

s^{- 1}

, 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

16.01 %

and

17.45 %

, 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. Full article

(This article belongs to the Section Gravitation)

► Show Figures

Figure 1

12 pages, 2987 KiB

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

Cited by 1 | Viewed by 1024

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. Full article

(This article belongs to the Special Issue Advances in Star Formation in the Milky Way)

► Show Figures

Figure 1

14 pages, 295 KiB

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

Cited by 1 | Viewed by 701

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 [...] Read more.

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. Full article

(This article belongs to the Collection Modified Theories of Gravity and Cosmological Applications)

17 pages, 6903 KiB

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

Viewed by 949

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. Full article

(This article belongs to the Section Planetary Sciences)

► Show Figures

Figure 1

17 pages, 4734 KiB

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

Cited by 1 | Viewed by 829

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. Full article

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

► Show Figures

Figure 1

15 pages, 3006 KiB

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

Viewed by 1529

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. Full article

(This article belongs to the Section Astroinformatics and Astrostatistics)

► Show Figures

Figure 1

4 pages, 178 KiB

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

Viewed by 855

Abstract

This Special Issue is a collection of reviews highlighting the recent progress in the very vast and closely related fields of

γ

-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)

18 pages, 967 KiB

Open AccessArticle

Gravitating Scalarons with Inverted Higgs Potential

by Xiao Yan Chew and Kok-Geng Lim

Universe 2024, 10(5), 212; https://doi.org/10.3390/universe10050212 - 10 May 2024

Cited by 3 | Viewed by 1186

Abstract

Previously, a class of regular and asymptotically flat gravitating scalar solitons (scalarons) has been constructed in the Einstein–Klein–Gordon (EKG) theory by adopting a phantom field with Higgs-like potential where the kinetic term has the wrong sign and the scalaron possesses the negative Arnowitt–Deser–Misner [...] Read more.

Previously, a class of regular and asymptotically flat gravitating scalar solitons (scalarons) has been constructed in the Einstein–Klein–Gordon (EKG) theory by adopting a phantom field with Higgs-like potential where the kinetic term has the wrong sign and the scalaron possesses the negative Arnowitt–Deser–Misner (ADM) mass as a consequence. In this paper, we demonstrate that the use of the phantom field can be avoided by inverting the Higgs-like potential in the EKG system when the kinetic term has a proper sign, such that the corresponding gravitating scalaron can possess the positive ADM mass. We systematically study the basic properties of the gravitating scalaron, such as the ADM mass, the energy conditions, the geodesics of test particles, etc. Moreover, we find that it can be smoothly connected to the counterpart hairy black hole solutions from our recent work in the small horizon limit. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)

► Show Figures

Figure 1

23 pages, 603 KiB

Open AccessArticle

PeV-Scale SUSY and Cosmic Strings from F-Term Hybrid Inflation

by Constantinos Pallis

Universe 2024, 10(5), 211; https://doi.org/10.3390/universe10050211 - 8 May 2024

Cited by 9 | Viewed by 778

Abstract

We consider F-term hybrid inflation (FHI) and SUSY breaking in the context of a

B - L

extension of the MSSM that largely respects a global

U (1)

R symmetry. The hidden sector Kaehler manifold enjoys an enhanced [...] Read more.

We consider F-term hybrid inflation (FHI) and SUSY breaking in the context of a

B - L

extension of the MSSM that largely respects a global

U (1)

R symmetry. The hidden sector Kaehler manifold enjoys an enhanced

S U (1, 1) / U (1)

symmetry, with the scalar curvature determined by the achievement of a SUSY-breaking de Sitter vacuum without undesirable tuning. FHI turns out to be consistent with the data, provided that the magnitude of the emergent soft tadpole term is confined to the range

(1.2

–

100)

TeV, and it is accompanied by the production of

B - L

cosmic strings. If these are metastable, they are consistent with the present observations from PTA experiments on the stochastic background of gravitational waves with dimensionless tension

G μ_{cs} ≃ (1 - 9.2) \cdot 10^{- 8}

. The

μ

parameter of the MSSM arises by appropriately adapting the Giudice–Masiero mechanism and facilitates the out-of-equilibrium decay of the R saxion at a reheat temperature lower than about 71 GeV. Due to the prolonged matter-dominated era, the gravitational wave signal is suppressed at high frequencies. The SUSY mass scale turns out to lie in the PeV region. Full article

(This article belongs to the Special Issue Probing the Early Universe)

► Show Figures

Figure 1

28 pages, 5646 KiB

Open AccessReview

Artificial Intelligence in Astronomical Optical Telescopes: Present Status and Future Perspectives

by Kang Huang, Tianzhu Hu, Jingyi Cai, Xiushan Pan, Yonghui Hou, Lingzhe Xu, Huaiqing Wang, Yong Zhang and Xiangqun Cui

Universe 2024, 10(5), 210; https://doi.org/10.3390/universe10050210 - 8 May 2024

Cited by 1 | Viewed by 1588

Abstract

With new artificial intelligence (AI) technologies and application scenarios constantly emerging, AI technology has become widely used in astronomy and has promoted notable progress in related fields. A large number of papers have reviewed the application of AI technology in astronomy. However, relevant [...] Read more.

With new artificial intelligence (AI) technologies and application scenarios constantly emerging, AI technology has become widely used in astronomy and has promoted notable progress in related fields. A large number of papers have reviewed the application of AI technology in astronomy. However, relevant articles seldom mention telescope intelligence separately, and it is difficult to understand the current development status of and research hotspots in telescope intelligence from these papers. This paper combines the development history of AI technology and difficulties with critical telescope technologies, comprehensively introduces the development of and research hotspots in telescope intelligence, conducts a statistical analysis of various research directions in telescope intelligence, and defines the merits of these research directions. A variety of research directions are evaluated, and research trends in each type of telescope intelligence are indicated. Finally, according to the advantages of AI technology and trends in telescope development, potential future research hotspots in the field of telescope intelligence are given. Full article

(This article belongs to the Section Space Science)

► Show Figures

Figure 1

16 pages, 1262 KiB

Open AccessArticle

Cosmological Inference from within the Peculiar Local Universe

by Roya Mohayaee, Mohamed Rameez and Subir Sarkar

Universe 2024, 10(5), 209; https://doi.org/10.3390/universe10050209 - 7 May 2024

Cited by 20 | Viewed by 1040

Abstract

The existence of ‘peculiar’ velocities due to the formation of cosmic structure marks a point of discord between the real universe and the usually assumed Friedmann–Lemaítre–Robertson–Walker metric, which accomodates only the smooth Hubble expansion on large scales. In the standard

Λ

CDM model [...] Read more.

The existence of ‘peculiar’ velocities due to the formation of cosmic structure marks a point of discord between the real universe and the usually assumed Friedmann–Lemaítre–Robertson–Walker metric, which accomodates only the smooth Hubble expansion on large scales. In the standard

Λ

CDM model framework, Type Ia supernovae data are routinely “corrected” for the peculiar velocities of both the observer and the supernova host galaxies relative to the cosmic rest frame, in order to infer evidence for acceleration of the expansion rate from their Hubble diagram. However, observations indicate a strong, coherent local bulk flow that continues outward without decaying out to a redshift

z ≳ 0.1

, contrary to the

Λ

CDM expectation. By querying the halo catalogue of the Dark Sky Hubble-volume N-body simulation, we find that an observer placed in an unusual environment like our local universe should see correlations between supernovae in the JLA catalogue that are 2–8 times stronger than seen by a typical or Copernican observer. This accounts for our finding that peculiar velocity corrections have a large impact on the value of the cosmological constant inferred from supernova data. We also demonstrate that local universe-like observers will infer a downward biased value of the clustering parameter

S_{8}

from comparing the density and velocity fields. More realistic modelling of the peculiar local universe is thus essential for correctly interpreting cosmological data. Full article

(This article belongs to the Special Issue The Large-Scale Structure of the Universe: Theory and Observation)

► Show Figures

Figure 1

18 pages, 980 KiB

Open AccessArticle

Dip-Bump Structure in Proton’s Single Diffractive Dissociation at the Large Hadron Collider

by László Jenkovszky, Rainer Schicker and István Szanyi

Universe 2024, 10(5), 208; https://doi.org/10.3390/universe10050208 - 7 May 2024

Viewed by 915

Abstract

By extending the dipole Pomeron (DP) model, successful in describing elastic nucleon–nucleon scattering, to proton single diffractive dissociation (SD), we predict a dip-bump structure in the squared four-momentum transfer (t) distribution of proton’s SD. Structures in the t distribution of single [...] Read more.

By extending the dipole Pomeron (DP) model, successful in describing elastic nucleon–nucleon scattering, to proton single diffractive dissociation (SD), we predict a dip-bump structure in the squared four-momentum transfer (t) distribution of proton’s SD. Structures in the t distribution of single diffractive dissociation are predicted around

t = - 4

{GeV}^{2}

at LHC energies in the range of 3

{GeV}^{2}

≲ | t | ≲

7

{GeV}^{2}

. Apart from the dependence on s (total energy squared) and t (squared momentum transfer), we predict also a dependence on missing masses. We include the minimum set of Regge trajectories, namely the Pomeron and the Odderon, indispensable at the LHC. Further generalization, e.g., by the inclusion of non-leading Regge trajectories, is straightforward. The present model contains two types of Regge trajectories: those connected with

t

-channel exchanges (the Pomeron, the Odderon, and non-leading (secondary) reggeons) appearing at small and moderate

- t

, where they are real and nearly linear, as well as direct-channel trajectories

α (M^{2})

related to missing masses. In this paper, we concentrate on structures in t neglecting (for the time being) resonances in

M^{2}

. Full article

(This article belongs to the Special Issue Multiparticle Dynamics)

► Show Figures

Figure 1

15 pages, 1433 KiB

Open AccessArticle

Fast Radio Burst Energy Function in the Presence of DM_host Variation

by Ji-Guo Zhang, Yichao Li, Jia-Ming Zou, Ze-Wei Zhao, Jing-Fei Zhang and Xin Zhang

Universe 2024, 10(5), 207; https://doi.org/10.3390/universe10050207 - 6 May 2024

Cited by 4 | Viewed by 976

Abstract

Fast radio bursts (FRBs) have been found in great numbers, but the physical mechanism of these sources is still a mystery. The redshift evolutions of the FRB energy distribution function and the volumetric rate shed light on the origin of FRBs. However, such [...] Read more.

Fast radio bursts (FRBs) have been found in great numbers, but the physical mechanism of these sources is still a mystery. The redshift evolutions of the FRB energy distribution function and the volumetric rate shed light on the origin of FRBs. However, such estimations rely on the dispersion measurement (DM)–redshift (z) relationship. A few FRBs that have been detected recently show large excess DMs beyond the expectation from the cosmological and Milky Way contributions, which indicates large spread of DMs from their host galaxies. In this work, we adopt two lognormal-distributed

{DM}_{host}

models and estimate the energy function using the non-repeating FRBs selected from the Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB Catalog 1. By comparing the lognormal-distributed

{DM}_{host}

models to a constant

{DM}_{host}

model, the FRB energy function results are consistent within the measurement uncertainty. We also estimate the volumetric rate of the non-repeating FRBs in three different redshift bins. The volumetric rate shows that the trend is consistent with the stellar-mass density redshift evolution. Since the lognormal-distributed

{DM}_{host}

model increases the measurement errors, the inference of FRBs tracking the stellar-mass density is nonetheless undermined. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—'Cosmology')

► Show Figures

Figure 1

7 pages, 246 KiB

Open AccessCommunication

Measuring a Gravitomagnetic Effect with the Triple Pulsar PSR J0337+1715

by Lorenzo Iorio

Universe 2024, 10(5), 206; https://doi.org/10.3390/universe10050206 - 6 May 2024

Cited by 1 | Viewed by 1111

Abstract

To the first post-Newtonian order, the orbital angular momentum of the fast-revolving inner binary of the triple system PSR J0337+1715, made of a millisecond pulsar and a white dwarf, induces an annular gravitomagnetic field which displaces the line of apsides of the slower [...] Read more.

To the first post-Newtonian order, the orbital angular momentum of the fast-revolving inner binary of the triple system PSR J0337+1715, made of a millisecond pulsar and a white dwarf, induces an annular gravitomagnetic field which displaces the line of apsides of the slower orbit of the other, distant white dwarf by

- 1.2

milliarcseconds per year. The current accuracy in determining the periastron of the outer orbit is

63.9

milliarcseconds after 1.38 years of data collection. By hypothesizing a constant rate of measurement of the pulsar’s times of arrivals over the next 10 years, assumed equal to the present one, it can be argued that the periastron will be finally known to a ≃

0.15

milliarcseconds level, while its cumulative gravitomagnetic retrograde shift will be as large as

- 12

milliarcseconds. The competing post-Newtonian gravitolectric periastron advance due to the inner binary’s masses, nominally amounting to

74.3

milliarcseconds per year, can be presently modelled to an accuracy level as good as ≃

0.04

milliarcseconds per year. The mismodeling in the much larger Newtonian periastron rate due to the quadrupolar term of the multipolar expansion of the gravitational potential of a massive ring representing the inner binary, whose nominal size for PSR J0337+1715 is

0.17

degrees per year, might be reduced down to the ≃

0.5

milliarcseconds per year level over the next 10 years. Thus, a first measurement of such a novel form of gravitomagnetism, although undoubtedly challenging, might be, perhaps, feasible in a not too distant future. Full article

(This article belongs to the Section Gravitation)

19 pages, 686 KiB

Open AccessArticle

Probing the Propeller Regime with Symbiotic X-ray Binaries

by Marina D. Afonina and Sergei B. Popov

Universe 2024, 10(5), 205; https://doi.org/10.3390/universe10050205 - 3 May 2024

Cited by 2 | Viewed by 975

Abstract

At the moment, there are two neutron star X-ray binaries with massive red supergiants as donors. Recently, De et al. (2023) proposed that the system SWIFT J0850.8-4219 contains a neutron star at the propeller stage. We study this possibility by applying various models [...] Read more.

At the moment, there are two neutron star X-ray binaries with massive red supergiants as donors. Recently, De et al. (2023) proposed that the system SWIFT J0850.8-4219 contains a neutron star at the propeller stage. We study this possibility by applying various models of propeller spin-down. We demonstrate that the duration of the propeller stage is very sensitive to the regime of rotational losses. Only in the case of a relatively slow propeller model proposed by Davies and Pringle in 1981, the duration of the propeller is long enough to provide a significant probability to observe the system at this stage. Future determination of the system parameters (orbital and spin periods, magnetic field of the compact object, etc.) will allow putting strong constraints on the propeller behavior. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)

► Show Figures

Figure 1

14 pages, 409 KiB

Open AccessArticle

Impact of Newly Measured Nuclear Reaction Rates on ²⁶Al Ejected Yields from Massive Stars

by Umberto Battino, Lorenzo Roberti, Thomas V. Lawson, Alison M. Laird and Lewis Todd

Universe 2024, 10(5), 204; https://doi.org/10.3390/universe10050204 - 1 May 2024

Viewed by 1150

Abstract

Over the last three years, the rates of all the main nuclear reactions involving the destruction and production of ²⁶Al in stars (²⁶Al(n, p)²⁶Mg, ²⁶Al(n, α)²³Na, ²⁶Al(p [...] Read more.

Over the last three years, the rates of all the main nuclear reactions involving the destruction and production of ²⁶Al in stars (²⁶Al(n, p)²⁶Mg, ²⁶Al(n, α)²³Na, ²⁶Al(p, γ)²⁷Si and ²⁵Mg(p, γ)²⁶Al) have been re-evaluated thanks to new high-precision experimental measurements of their crosssections at energies of astrophysical interest, considerably reducing the uncertainties in the nuclear physics affecting their nucleosynthesis. We computed the nucleosynthetic yields ejected by the explosion of a high-mass star (20 M_⊙, Z = 0.0134) using the FRANEC stellar code, considering two explosion energies, 1.2 × 10⁵¹ erg and 3 × 10⁵¹ erg. We quantify the change in the ejected amount of ²⁶Al and other key species that is predicted when the new rate selection is adopted instead of the reaction rates from the STARLIB nuclear library. Additionally, the ratio of our ejected yields of ²⁶Al to those of 14 other short-lived radionuclides (³⁶Cl, ⁴¹Ca, ⁵³Mn, ⁶⁰Fe, ⁹²Nb, ⁹⁷Tc, ⁹⁸Tc, ¹⁰⁷Pd, ¹²⁶Sn, ¹²⁹I, ³⁶Cs, ¹⁴⁶Sm, ¹⁸²Hf, ²⁰⁵Pb) are compared to early solar system isotopic ratios, inferred from meteorite measurements. The total ejected ²⁶Al yields vary by a factor of ~3 when adopting the new rates or the STARLIB rates. Additionally, the new nuclear reaction rates also impact the predicted abundances of short-lived radionuclides in the early solar system relative to ²⁶Al. However, it is not possible to reproduce all the short-lived radionuclide isotopic ratios with our massive star model alone, unless a second stellar source could be invoked, which must have been active in polluting the pristine solar nebula at a similar time of a core-collapse supernova. Full article

(This article belongs to the Special Issue Recent Outcomes and Future Challenges in Nuclear Astrophysics)

► Show Figures

Figure 1

19 pages, 7408 KiB

Open AccessReview

Supernova Remnants in Gamma Rays

by Andrea Giuliani and Martina Cardillo

Universe 2024, 10(5), 203; https://doi.org/10.3390/universe10050203 - 1 May 2024

Viewed by 1210

Abstract

In the 1960s, the remnants of supernova explosions (SNRs) were indicated as a possible source of galactic cosmic rays through the Diffusive Shock Acceleration (DSA) mechanism. Since then, the observation of gamma-ray emission from relativistic ions in these objects has been one of [...] Read more.

In the 1960s, the remnants of supernova explosions (SNRs) were indicated as a possible source of galactic cosmic rays through the Diffusive Shock Acceleration (DSA) mechanism. Since then, the observation of gamma-ray emission from relativistic ions in these objects has been one of the main goals of high-energy astrophysics. A few dozen SNRs have been detected at GeV and TeV photon energies in the last two decades. However, these observations have shown a complex phenomenology that is not easy to reduce to the standard paradigm based on DSA acceleration. Although the understanding of these objects has greatly increased, and their nature as efficient electron and proton accelerators has been observed, it remains to be clarified whether these objects are the main contributors to galactic cosmic rays. Here, we review the observations of

γ

-ray emission from SNRs and the perspectives for the future. Full article

(This article belongs to the Special Issue Recent Advances in Gamma Ray Astrophysics and Future Perspectives)

► Show Figures

Figure 1

38 pages, 6475 KiB

Open AccessArticle

Theory of Majorana-Type Heavy Ion Double Charge Exchange Reactions by Pion–Nucleon Isotensor Interactions

by Horst Lenske, Jessica Bellone, Maria Colonna and Danilo Gambacurta

Universe 2024, 10(5), 202; https://doi.org/10.3390/universe10050202 - 30 Apr 2024

Viewed by 899

Abstract

The theory of heavy ion double charge exchange (DCE) reactions proceeding by effective rank-2 isotensor interactions is presented. Virtual pion–nucleon charge exchange interactions are investigated as the source for induced isotensor interactions, giving rise to the Majorana DCE (MDCE) reaction mechanism. MDCE is [...] Read more.

The theory of heavy ion double charge exchange (DCE) reactions proceeding by effective rank-2 isotensor interactions is presented. Virtual pion–nucleon charge exchange interactions are investigated as the source for induced isotensor interactions, giving rise to the Majorana DCE (MDCE) reaction mechanism. MDCE is of a generic character, proceeding through pairs of complementary (

π^{\pm}, π^{\mp}

) reactions in the projectile and target nucleus. The dynamics of the elementary processes is discussed, where the excitation of pion–nucleon resonances are of central importance. Investigations of initial and final state ion–ion interactions show that these effects are acting as vertex renormalizations. In closure approximation, well justified by the finite pion mass, the second-order transition matrix elements reduce to pion potentials and effective two-body isotensor DCE interactions, giving rise also to two-body correlations in either of the participating nuclei. Connections to neutrinoless Majorana double beta decay (MDBD) are elucidated at various levels of the dynamics, from the underlying fundamental electro-weak and QCD scales to the physical scales of nuclear MDBD and MDCE physics. It is pointed out that heavy ion MDCE reactions may also proceed by competing electro-weak charge exchange processes, leading to lepton MDCE by electrons, positrons, and neutrinos. Full article

(This article belongs to the Special Issue Recent Advances in Double Beta Decay Investigations: In Honor of Prof. Sabin Stoica at His 70th Anniversary)

► Show Figures

Figure 1

13 pages, 872 KiB

Open AccessArticle

An Investigation of the Loop Oscillations after a Solar Flare

by Jun Xu, Zongjun Ning, Dong Li, Fanpeng Shi, Yuxiang Song and Yuzhi Yang

Universe 2024, 10(5), 201; https://doi.org/10.3390/universe10050201 - 29 Apr 2024

Viewed by 948

Abstract

We study the loop oscillations after a solar flare on 19 January 2023, in the active region N11E40 3196, which is well observed by the SDO/AIA. After tracing the loop position and fitting, we find that the loop oscillations have a period between [...] Read more.

We study the loop oscillations after a solar flare on 19 January 2023, in the active region N11E40 3196, which is well observed by the SDO/AIA. After tracing the loop position and fitting, we find that the loop oscillations have a period between 3 and 9 min at various locations, such as from the leg to the top or from the inner to the outer loop. Their oscillating amplitudes decrease with time. Two loops display the position oscillation simultaneously with their brightness oscillation. After the analysis of the differential emission measure (DEM), we find that two of their loop position oscillations resulted from the plasma density fluctuation. Meanwhile, it is interesting that the brightness of these two position oscillations displays a typical period of about 4 min, similar to that of the position oscillation. This is possible due to both the plasma density and temperature fluctuation there. Our findings provide the physical clues for studying and understanding the mechanism of the loop position and brightness oscillations. Full article

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

► Show Figures

Figure 1

10 pages, 1067 KiB

Open AccessArticle

Variation in X_CO Factor in N55 Region

by Qiang Li, Mingyue Li, Li Zhang and Songpeng Pei

Universe 2024, 10(5), 200; https://doi.org/10.3390/universe10050200 - 29 Apr 2024

Viewed by 1173

Abstract

The

X_{C O}

factor is defined as

X_{C O} = N (H_{2}) / W_{12 C O}

. It is useful for estimating cloud mass. However, there is only limited research on how the

X_{C O}

factor [...] Read more.

The

X_{C O}

factor is defined as

X_{C O} = N (H_{2}) / W_{12 C O}

. It is useful for estimating cloud mass. However, there is only limited research on how the

X_{C O}

factor varies within a single cloud. Employing ¹²

C O (J = 1-0)

and ¹³

C O (J = 1-0)

spectral data, we computed an

X_{C O}

factor of 3.6

\times 10^{20} {cm}^{- 2}

(K km s⁻¹)⁻¹ for luminous gas of the N55 region. Our analysis revealed a V-shaped correlation between the

X_{C O}

factor and

H_{2}

column densities, while the relationship with excitation temperature exhibited obscurity. This suggests that the CO-to-

H_{2}

conversion is not consistent on small scale (∼1 pc). Additionally, we found that star formation activity has little influence on the variability in the

X_{C O}

factor. Full article

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

► Show Figures

Figure 1

Journal Menu

Journal Browser

Universe, Volume 10, Issue 5 (May 2024) – 41 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI