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
An Investigation on the Distribution of Martian Ionospheric Particles, Based on the Mars Atmosphere and Volatile Evolution (MAVEN)
Universe 2024, 10(5), 196; https://doi.org/10.3390/universe10050196 - 26 Apr 2024
Abstract
In this paper, we use the key parameters data set of the Neutral Gas and Ion Mass Spectrometer from the Mars Atmosphere and Volatile Evolution (MAVEN) mission. The particle density profiles of electrons, / ,
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In this paper, we use the key parameters data set of the Neutral Gas and Ion Mass Spectrometer from the Mars Atmosphere and Volatile Evolution (MAVEN) mission. The particle density profiles of electrons, / , , , , , and from 90 to 500 km have been deduced by adopting the Chapman modeling methodology. The correlation of the peak density/altitude with the solar zenith angle, the changes in the profile of the Martian ionosphere during solar flares, and the effects of Martian dust storms are analyzed. The results exhibit a positive/negative correlation between the peak density/altitude of the M2 layer and the solar zenith angle. Within the MAVEN observational record available, only three C-Class flares occurred on 26 August 2016, 29 November 2020, and 26 August 2021. The analysis reveals during these solar flare events, the electron density of the M2 layer above 200 km increases obviously. The peak density of M1 increases by 33.4%, 13.2% and 7.4%, while the peak height decreases by 0.1%, 10.2% and 4.4%, respectively. The Martian dust storm causes the peak height of the M2 layer to increase by 19.5 km, and the peak density to decrease by 4.2 × . Our study shows that the Martian ionosphere is similar to the Earth’s, which is of great significance for understanding the planetary ionosphere.
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(This article belongs to the Special Issue Planetary Space Weather)
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Shanghai Tianma Radio Telescope and Its Role in Pulsar Astronomy
by
Zhen Yan, Zhiqiang Shen, Yajun Wu, Rongbing Zhao, Jie Liu, Zhipeng Huang, Rui Wang, Xiaowei Wang, Qinghui Liu, Bin Li, Jinqing Wang, Weiye Zhong, Wu Jiang and Bo Xia
Universe 2024, 10(5), 195; https://doi.org/10.3390/universe10050195 - 26 Apr 2024
Abstract
After two phases of on-site construction and testing (2010–2013 and 2013–2017), the Shanghai Tianma Radio Telescope (TMRT) can work well, with efficiencies better than 50% from 1.3 to 50.0 GHz, mainly benefiting from its low-noise cryogenic receivers and active surface system. Pulsars were
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After two phases of on-site construction and testing (2010–2013 and 2013–2017), the Shanghai Tianma Radio Telescope (TMRT) can work well, with efficiencies better than 50% from 1.3 to 50.0 GHz, mainly benefiting from its low-noise cryogenic receivers and active surface system. Pulsars were chosen as important targets of research at the TMRT because of their important scientific and applied values. To meet the demands of pulsar-related observations, TMRT is equipped with some necessary backends, including a digital backend system (DIBAS) supporting normal pulsar observation modes, a real-time fast-radio-burst-monitoring backend, and baseband backends for very-long-baseline interferometry (VLBI) observations. Utilizing its high sensitivity and simultaneous dual-frequency observation capacity, a sequence of pulsar research endeavors has been undertaken, such as long-term pulsar timing, magnetar monitoring, multi-frequency (or high-frequency) observations, interstellar scintillation, pulsar VLBI, etc. In this paper, we give a short introduction about pulsar observation systems at the TMRT and briefly review the results obtained by these pulsar research projects.
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(This article belongs to the Special Issue Pulsar Astronomy)
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Changes in and Recovery of the Turbulence Properties in the Magnetosheath for Different Solar Wind Streams
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Liudmila Rakhmanova, Alexander Khokhlachev, Maria Riazantseva, Yuri Yermolaev and Georgy Zastenker
Universe 2024, 10(5), 194; https://doi.org/10.3390/universe10050194 - 26 Apr 2024
Abstract
Solar wind is known to have different properties depending on its origin at the Sun. In addition to the differences in plasma and magnetic field parameters, these streams differ due to the properties of turbulent fluctuations involved in the flow. The present study
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Solar wind is known to have different properties depending on its origin at the Sun. In addition to the differences in plasma and magnetic field parameters, these streams differ due to the properties of turbulent fluctuations involved in the flow. The present study addresses the changes in the turbulence properties in the magnetosheath—the transition region in front of the magnetosphere. This study is based on statistics from the simultaneous measurements of magnetic field fluctuations in the solar wind and in the magnetosheath. Both the dayside and flank magnetosheath regions are focused on to detect the evolution of the turbulent fluctuations during their flow around the magnetosphere. Turbulent cascade is shown to save its properties for fast solar wind streams. Conditions favorable for the preservation of the turbulence properties at the bow shock may correspond to the increased geoefficiency of large-scale solar wind structures.
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(This article belongs to the Section Space Science)
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Cosmological Test of an Ultraviolet Origin of Dark Energy
by
Hans Christiansen, Bence Takács and Steen H. Hansen
Universe 2024, 10(5), 193; https://doi.org/10.3390/universe10050193 - 25 Apr 2024
Abstract
The accelerated expansion of the Universe is impressively well described by a cosmological constant. However, the observed value of the cosmological constant is much smaller than expected based on quantum field theories. Recent efforts to achieve consistency in these theories have proposed a
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The accelerated expansion of the Universe is impressively well described by a cosmological constant. However, the observed value of the cosmological constant is much smaller than expected based on quantum field theories. Recent efforts to achieve consistency in these theories have proposed a relationship between Dark Energy and the most compact objects, such as black holes (BHs). However, experimental tests are very challenging to devise and perform. In this article, we present a testable model with no cosmological constant in which the accelerated expansion can be driven by black holes. The model couples the expansion of the Universe (the Friedmann equation) with the mass function of cosmological halos (using the Press–Schechter formalism). Through the observed link between halo masses and BH masses, one thus gets a coupling between the expansion rate of the Universe and the BHs. We compare the predictions of this simple BH model with SN1a data and find poor agreement with observations. Our method is sufficiently general to allow us to also test a fundamentally different model, also without a cosmological constant, where the accelerated expansion is driven by a new force proportional to the internal velocity dispersion of galaxies. Surprisingly enough, this model cannot be excluded using the SN1a data.
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(This article belongs to the Special Issue The Nature of Dark Energy)
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Non-Commutative Classical and Quantum Fractionary Cosmology: FRW Case
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J. Socorro, J. Juan Rosales and Leonel Toledo-Sesma
Universe 2024, 10(5), 192; https://doi.org/10.3390/universe10050192 - 25 Apr 2024
Abstract
In this work, we will explore the effects of non-commutativity in fractional classical and quantum schemes using the flat Friedmann–Robertson–Walker (FRW) cosmological model coupled to a scalar field in the K-essence formalism. In previous work, we have obtained the commutative solutions in both
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In this work, we will explore the effects of non-commutativity in fractional classical and quantum schemes using the flat Friedmann–Robertson–Walker (FRW) cosmological model coupled to a scalar field in the K-essence formalism. In previous work, we have obtained the commutative solutions in both regimes in the fractional framework. Here, we introduce non-commutative variables, considering that all minisuperspace variables do not commute, so the symplectic structure was modified. In the quantum regime, the probability density presents a new structure in the scalar field corresponding to the value of the non-commutative parameter, in the sense that this probability density undergoes a shift back to the direction of the scale factor, causing classical evolution to arise earlier than in the commutative world.
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(This article belongs to the Special Issue Recent Advances in Quantum Cosmology)
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Combining Empirical and Physics-Based Models for Solar Wind Prediction
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Rob Johnson, Soukaina Filali Boubrahimi, Omar Bahri and Shah Muhammad Hamdi
Universe 2024, 10(5), 191; https://doi.org/10.3390/universe10050191 - 24 Apr 2024
Abstract
Solar wind modeling is classified into two main types: empirical models and physics-based models, each designed to forecast solar wind properties in various regions of the heliosphere. Empirical models, which are cost-effective, have demonstrated significant accuracy in predicting solar wind at the L1
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Solar wind modeling is classified into two main types: empirical models and physics-based models, each designed to forecast solar wind properties in various regions of the heliosphere. Empirical models, which are cost-effective, have demonstrated significant accuracy in predicting solar wind at the L1 Lagrange point. On the other hand, physics-based models rely on magnetohydrodynamics (MHD) principles and demand more computational resources. In this research paper, we build upon our recent novel approach that merges empirical and physics-based models. Our recent proposal involves the creation of a new physics-informed neural network that leverages time series data from solar wind predictors to enhance solar wind prediction. This innovative method aims to combine the strengths of both modeling approaches to achieve more accurate and efficient solar wind predictions. In this work, we show the variability of the proposed physics-informed loss across multiple deep learning models. We also study the effect of training the models on different solar cycles on the model’s performance. This work represents the first effort to predict solar wind by integrating deep learning approaches with physics constraints and analyzing the results across three solar cycles. Our findings demonstrate the superiority of our physics-constrained model over other unconstrained deep learning predictive models.
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(This article belongs to the Special Issue Solar and Stellar Activity: Exploring the Cosmic Nexus)
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Betti Functionals as Probes for Cosmic Topology
by
Ralf Aurich and Frank Steiner
Universe 2024, 10(5), 190; https://doi.org/10.3390/universe10050190 - 24 Apr 2024
Abstract
The question of the global topology of the Universe (cosmic topology) is still open. In the CDM concordance model, it is assumed that the space of the Universe possesses the trivial topology of , and thus that the Universe has
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The question of the global topology of the Universe (cosmic topology) is still open. In the CDM concordance model, it is assumed that the space of the Universe possesses the trivial topology of , and thus that the Universe has an infinite volume. As an alternative, in this paper, we study one of the simplest non-trivial topologies given by a cubic 3-torus describing a universe with a finite volume. To probe cosmic topology, we analyze certain structure properties in the cosmic microwave background (CMB) using Betti functionals and the Euler characteristic evaluated on excursions sets, which possess a simple geometrical interpretation. Since the CMB temperature fluctuations are observed on the sphere surrounding the observer, there are only three Betti functionals , . Here, denotes the temperature threshold normalized by the standard deviation of . The analytic approximations of the Gaussian expectations for the Betti functionals and an exact formula for the Euler characteristic are given. It is shown that the amplitudes of and decrease with an increasing volume of the cubic 3-torus universe. Since the computation of the ’s from observational sky maps is hindered due to the presence of masks, we suggest a method that yields lower and upper bounds for them and apply it to four Planck 2018 sky maps. It is found that the ’s of the Planck maps lie between those of the torus universes with side-lengths and in units of the Hubble length and above the infinite CDM case. These results give a further hint that the Universe has a non-trivial topology.
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(This article belongs to the Section Cosmology)
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CP Conservation in the Strong Interactions
by
Wen-Yuan Ai, Björn Garbrecht and Carlos Tamarit
Universe 2024, 10(5), 189; https://doi.org/10.3390/universe10050189 - 23 Apr 2024
Abstract
We discuss matters related to the point that topological quantization in the strong interaction is a consequence of an infinite spacetime volume. Because of the ensuing order of limits, i.e., infinite volume prior to summing over topological sectors, is conserved. Here,
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We discuss matters related to the point that topological quantization in the strong interaction is a consequence of an infinite spacetime volume. Because of the ensuing order of limits, i.e., infinite volume prior to summing over topological sectors, is conserved. Here, we show that this reasoning is consistent with the construction of the path integral from steepest-descent contours. We reply to some objections that aim to support the case for violation in strong interactions that are based on the role of the -odd theta-parameter in three-form effective theories, the correct sampling of all configurations in the dilute instanton gas approximation and the volume dependence of the partition function. We also show that the chiral effective field theory derived from taking the volume to infinity first is in no contradiction with analyses based on partially conserved axial currents.
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(This article belongs to the Special Issue CP Violation and Flavor Physics)
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Two-Pion Bose–Einstein Correlations in Au+Au Collisions at
by
Anna Kraeva
Universe 2024, 10(4), 188; https://doi.org/10.3390/universe10040188 - 20 Apr 2024
Abstract
The correlation femtoscopy technique makes it possible to estimate the geometric dimensions and lifetime of the particle emission region after the collision of ions. Measurements of the emission region characteristics not only at midrapidity but also at backward (forward) rapidity can provide new
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The correlation femtoscopy technique makes it possible to estimate the geometric dimensions and lifetime of the particle emission region after the collision of ions. Measurements of the emission region characteristics not only at midrapidity but also at backward (forward) rapidity can provide new information about the source and make it possible to impose constraints on the heavy-ion collision models. This work is devoted to revealing the dependence of the spatial and temporal parameters of the emission region of identical pions in Au+Au collisions at = 3 GeV from the fixed-target program of the STAR experiment. The extracted femtoscopic radii, , , , , and the correlation strength, , are presented as a function of collision centrality, pair rapidity, and transverse momentum. Physics implications will be discussed.
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(This article belongs to the Special Issue Multiparticle Dynamics)
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Future Perspectives for Gamma-ray Burst Detection from Space
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Enrico Bozzo, Lorenzo Amati, Wayne Baumgartner, Tzu-Ching Chang, Bertrand Cordier, Nicolas De Angelis, Akihiro Doi, Marco Feroci, Cynthia Froning, Jessica Gaskin, Adam Goldstein, Diego Götz, Jon E. Grove, Sylvain Guiriec, Margarita Hernanz, C. Michelle Hui, Peter Jenke, Daniel Kocevski, Merlin Kole, Chryssa Kouveliotou, Thomas Maccarone, Mark L. McConnell, Hideo Matsuhara, Paul O’Brien, Nicolas Produit, Paul S. Ray, Peter Roming, Andrea Santangelo, Michael Seiffert, Hui Sun, Alexander van der Horst, Peter Veres, Jianyan Wei, Nicholas White, Colleen Wilson-Hodge, Daisuke Yonetoku, Weimin Yuan and Shuang-Nan Zhangadd
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Universe 2024, 10(4), 187; https://doi.org/10.3390/universe10040187 - 19 Apr 2024
Abstract
Since their first discovery in the late 1960s, gamma-ray bursts have attracted an exponentially growing interest from the international community due to their central role in the most highly debated open questions of the modern research of astronomy, astrophysics, cosmology, and fundamental physics.
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Since their first discovery in the late 1960s, gamma-ray bursts have attracted an exponentially growing interest from the international community due to their central role in the most highly debated open questions of the modern research of astronomy, astrophysics, cosmology, and fundamental physics. These range from the intimate nuclear composition of high-density material within the core of ultra-dense neuron stars, to stellar evolution via the collapse of massive stars, the production and propagation of gravitational waves, as well as the exploration of the early universe by unveiling the first stars and galaxies (assessing also their evolution and cosmic re-ionization). GRBs in the past ∼50 years have stimulated the development of cutting-edge technological instruments for observations of high-energy celestial sources from space, leading to the launch and successful operations of many different scientific missions (several of them still in data-taking mode currently). In this review, we provide a brief description of the GRB-dedicated missions from space being designed and developed for the future. The list of these projects, not meant to be exhaustive, shall serve as a reference to interested readers to understand what is likely to come next to lead the further development of GRB research and the associated phenomenology.
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(This article belongs to the Special Issue Recent Advances in Gamma Ray Astrophysics and Future Perspectives)
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The Changes in Multiscale Solar Wind Fluctuations on the Path from the Sun to Earth
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Igor D. Volodin, Maria O. Riazantseva, Liudmila S. Rakhmanova, Alexander A. Khokhlachev and Yuri I. Yermolaev
Universe 2024, 10(4), 186; https://doi.org/10.3390/universe10040186 - 19 Apr 2024
Abstract
This paper is devoted to the analysis of fluctuations in the solar wind plasma and interplanetary magnetic field parameters observed by Solar Orbiter and WIND spacecraft at different scales ranging from ~103 to 107 km. We consider two long data intervals
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This paper is devoted to the analysis of fluctuations in the solar wind plasma and interplanetary magnetic field parameters observed by Solar Orbiter and WIND spacecraft at different scales ranging from ~103 to 107 km. We consider two long data intervals where the distances between the spacecraft are 0.1 and 0.5 AU, respectively, and they are located close to the Sun–Earth line. Transformation of the fluctuation’s properties on the way from the Sun to Earth is analyzed for different types of solar wind associated with quasi-stationary and transient solar phenomena. The time series of bulk speed are shown to undergo a slight modification, even for large spacecraft separation, while the time series of the interplanetary magnetic field magnitude and components as well as proton density may be transformed even at a relatively short distance. Though the large-scale solar wind structures propagate the distance up to 0.5 AU without significant change, local structures at smaller scales may be modified. The statistical properties of the fluctuations such as relative standard deviation or probability distribution function and its moments remain nearly unchanged at different distances between the two spacecraft and are likely to depend mostly on the type of the solar wind.
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(This article belongs to the Special Issue The Multi-Scale Dynamics of Solar Wind)
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The High Mass Accretion in the Innermost Regions of a Viscously Evolved Protoplanetary Disk
by
Chunjian Liu, Zhen Yao and Yue Quan
Universe 2024, 10(4), 185; https://doi.org/10.3390/universe10040185 - 18 Apr 2024
Abstract
In this paper, we investigate the mass accretion properties in the innermost regions of a viscously evolved protoplanetary disk and try to find some clues to the outburst events. In our newly developed one-dimensional time-dependent disk model based on the diffusion equation for
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In this paper, we investigate the mass accretion properties in the innermost regions of a viscously evolved protoplanetary disk and try to find some clues to the outburst events. In our newly developed one-dimensional time-dependent disk model based on the diffusion equation for surface density, we take into account the following physical effects: the gravitational collapse of the parent molecular cloud core, the irradiation from the central star to the disk, the effect of the photoevaporation mechanism, the viscosity due to the magnetorotational instability (MRI) and the gravitational instability (GI), and the thermal ionization mechanism in the inner regions. We find that the mass accretion rate in the innermost regions is statistically high enough to generate outbursts, although there are regions where the accretion rate is low. Additionally, we find that there is a weak correlation between the high mass accretion rate and the molecular cloud core’s properties (angular velocity and mass ), as well as a strong correlation with the minimum viscosity parameter . In general, there are two regions of outburst, the inner Region I and outer Region II. The outburst of Region I is caused by the MRI mechanism and thermal instability, while neither the MRI, the GI, nor the thermal instability causes the outburst of Region II. Our analysis suggests that the outer Region II is dominated by, or largely related to, the Rosseland mean opacity and the parameter.
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(This article belongs to the Section Planetary Sciences)
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Open AccessEditorial
Special Issue on Modified Gravity Approaches to the Tensions of ΛCDM: Goals and Highlights
by
Eleonora Di Valentino, Leandros Perivolaropoulos and Jackson Levi Said
Universe 2024, 10(4), 184; https://doi.org/10.3390/universe10040184 - 18 Apr 2024
Abstract
The standard cosmological model, known as CDM, has been remarkably successful in providing a coherent and predictive framework for understanding the Universe’s evolution, its large-scale structure, and cosmic microwave background (CMB) radiation [...]
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(This article belongs to the Special Issue Modified Gravity Approaches to the Tensions of ΛCDM)
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Linear Stability Analysis of Relativistic Magnetized Jets: The Minimalist Approach
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Nektarios Vlahakis
Universe 2024, 10(4), 183; https://doi.org/10.3390/universe10040183 - 17 Apr 2024
Abstract
A minimalist approach to the linear stability problem in fluid dynamics is developed that ensures efficiency by utilizing only the essential elements required to find the eigenvalues for given boundary conditions. It is shown that the problem is equivalent to a single first-order
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A minimalist approach to the linear stability problem in fluid dynamics is developed that ensures efficiency by utilizing only the essential elements required to find the eigenvalues for given boundary conditions. It is shown that the problem is equivalent to a single first-order ordinary differential equation, and that studying the argument of the unknown complex function in the eigenvalue space is sufficient to find the dispersion relation. The method is applied to a model for relativistic magnetized astrophysical jets.
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(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)
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The Statistical Analysis of Exoplanet and Host Stars Based on Multi-Satellite Data Observations
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Yanke Tang, Xiaolu Li, Kai Xiao, Ning Gai, Shijie Li, Futong Dong, Yifan Wang and Yang Gao
Universe 2024, 10(4), 182; https://doi.org/10.3390/universe10040182 - 16 Apr 2024
Abstract
In recent years, the rapid development of exoplanet research has provided us with an opportunity to better understand planetary systems in the universe and to search for signs of life. In order to further investigate the prevalence of habitable exoplanets and to validate
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In recent years, the rapid development of exoplanet research has provided us with an opportunity to better understand planetary systems in the universe and to search for signs of life. In order to further investigate the prevalence of habitable exoplanets and to validate planetary formation theories, as well as to comprehend planetary evolution, we have utilized confirmed exoplanet data obtained from the NASA Exoplanet Archive database, including data released by telescopes such as Kepler and TESS. By analyzing these data, we have selected a sample of planets around F, G, K, and M-type stars within a radius range of 1 to 20 and with orbital periods ranging from 0.4 days to 400 days. Using the IDEM method based on these data, we calculated the overall formation rate, which is estimated to be 2.02%. Then, we use these data to analyze the relationship among planet formation rates, stellar metallicity, and stellar gravitational acceleration ( ). We firstly find that the formation rate of giant planets is higher around metal-rich stellars, but it inhibits the formation of gas giants when > 4.5, yet the stellar metallicity seems to have no effect on the formation rate of smaller planets. Secondly, the host stellar gravitational acceleration affects the relationship between planet formation rate and orbital period. Thirdly, there is a robust power-law relationship between the orbital period of smaller planets and their formation rate. Finally, we find that, for a given orbital period, there is a positive correlation between the planet formation rate and the .
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(This article belongs to the Topic Techniques and Science Exploitations for Earth Observation and Planetary Exploration)
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Causal Structure in Spin Foams
by
Eugenio Bianchi and Pierre Martin-Dussaud
Universe 2024, 10(4), 181; https://doi.org/10.3390/universe10040181 - 14 Apr 2024
Abstract
The metric field of general relativity is almost fully determined by its causal structure. Yet, in spin foam models of quantum gravity, the role played by the causal structure is still largely unexplored. The goal of this paper is to clarify how causality
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The metric field of general relativity is almost fully determined by its causal structure. Yet, in spin foam models of quantum gravity, the role played by the causal structure is still largely unexplored. The goal of this paper is to clarify how causality is encoded in such models. The quest unveils the physical meaning of the orientation of the two-complex and its role as a dynamical variable. We propose a causal version of the EPRL spin foam model and discuss the role of the causal structure in the reconstruction of a semiclassical space–time geometry.
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(This article belongs to the Special Issue Loop Quantum Gravity: A Themed Issue in Honor of Prof. Abhay Ashtekar)
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Small-Scale Cosmology Independent of the Standard Model
by
Georgy I. Burde
Universe 2024, 10(4), 180; https://doi.org/10.3390/universe10040180 - 13 Apr 2024
Abstract
‘Small-scale cosmology’ is a theory designed to incorporate the linear redshift versus distance relation, which is inferred from observations, into the theoretical framework independent of the global Robertson–Walker–Friedman (RWF)-type models. The motivation behind this is that the RWF cosmological models, based on the
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‘Small-scale cosmology’ is a theory designed to incorporate the linear redshift versus distance relation, which is inferred from observations, into the theoretical framework independent of the global Robertson–Walker–Friedman (RWF)-type models. The motivation behind this is that the RWF cosmological models, based on the assumptions of homogeneity and a constant matter density, as well as the concept of expanding space inherent to them are not applicable on the scales of observations from which the linear Hubble law is inferred. Therefore, explaining the Hubble law as the small redshift limit of the RWF model or as an effect of expanding space is inconsistent. Thus, the Hubble linear relation between the redshift of an extragalactic object and its distance should be considered an independent law of nature valid in the range of the distances where the RWF cosmology is not valid. In general, the theory, based on that concept, can be developed in different ways. In the present paper, ‘small-scale cosmology’ is formulated as a theory operating in the (redshift–object coordinates) space, which allows developing a conceptual and computational basis of the theory along the lines of that of special relativity. In such a theory, the condition of invariance of the Hubble law with respect to a change in the observer acceleration plays a central role. In pursuing this approach, the effectiveness of group theoretical methods is exploited. Applying the Lie group method yields transformations of the variables (the redshift and space coordinates of a cosmological object) between the reference frames of the accelerated observers. In this paper, the transformations are applied to studying the effects of the solar system observer acceleration on the observed shape, distribution and rotation curves of galaxy clusters.
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(This article belongs to the Special Issue Probing the Standard Model of Cosmology with Model-Independent Methods)
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Minkowskian Approach to the Pseudorange Navigation Equations
by
Ramón Serrano Montesinos and Juan Antonio Morales-Lladosa
Universe 2024, 10(4), 179; https://doi.org/10.3390/universe10040179 - 12 Apr 2024
Abstract
Our starting point is the covariant coordinate transformation equation of a relativistic positioning system in Minkowski space–time that maps the receiver’s emission coordinates (proper times broadcast by the emitters) to its coordinates in some inertial reference frame. Bancroft’s analytical (closed-form) solution to the
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Our starting point is the covariant coordinate transformation equation of a relativistic positioning system in Minkowski space–time that maps the receiver’s emission coordinates (proper times broadcast by the emitters) to its coordinates in some inertial reference frame. Bancroft’s analytical (closed-form) solution to the basic pseudorange navigation equations with four emitters is recovered, and the subjacent elements are geometrically interpreted. The case of four static beacons is analysed as a clarifying situation.
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(This article belongs to the Section Gravitation)
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A New Solution of the Pulsar Equation
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Ioannis Contopoulos, Ioannis Dimitropoulos, Dimitris Ntotsikas and Konstantinos N. Gourgouliatos
Universe 2024, 10(4), 178; https://doi.org/10.3390/universe10040178 - 12 Apr 2024
Abstract
We present the first new type of solution of the pulsar equation since 1999. In it, the whole magnetosphere is confined inside the light cylinder and an electrically charged layer wraps around it and holds it together. The reason this new solution has
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We present the first new type of solution of the pulsar equation since 1999. In it, the whole magnetosphere is confined inside the light cylinder and an electrically charged layer wraps around it and holds it together. The reason this new solution has never been obtained before is that all current time-dependent simulations are initialized with a vacuum dipole configuration that extends to infinity; thus, their final steady-state solution also extends to infinity. Under special conditions, such a confined configuration may be attained when the neutron star first forms in the interior of a collapsing star during a supernova explosion, or when it accretes from an external wind or disk from a donor star. It is shown that this new maximally closed non-decelerating solution is the limit of a continuous sequence of standard magnetospheres with open and closed field lines when the amount of open field lines gradually drops to zero. The minimum energy solution in this sequence is a standard magnetosphere in which the closed field line region extends up to about of the light cylinder. We estimate that the released energy when the new solution transitions to the minimum energy one is enough to power a fast radio burst.
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(This article belongs to the Special Issue A New Horizon of Pulsar and Neutron Star: The 55-Year Anniversary)
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Open AccessCommunication
Upper Bound of Barrow Entropy Index from Black Hole Fragmentation
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Jiayi Xia and Yen Chin Ong
Universe 2024, 10(4), 177; https://doi.org/10.3390/universe10040177 - 11 Apr 2024
Abstract
Both classical and quantum arguments suggest that if Barrow entropy is correct, its index must be energy-dependent, which would affect the very early universe. Based on thermodynamic stability that sufficiently large black holes should not fragment, we argue that Barrow entropy correction
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Both classical and quantum arguments suggest that if Barrow entropy is correct, its index must be energy-dependent, which would affect the very early universe. Based on thermodynamic stability that sufficiently large black holes should not fragment, we argue that Barrow entropy correction must be small, except possibly at the Planckian regime. Furthermore, the fact that a solar mass black hole does not fragment implies an upper bound , which surprisingly lies in the same range as the bound obtained from some cosmological considerations assuming fixed . This indicates that allowing to run does not raise its allowed value. We briefly comment on the case of Kaniadakis entropy.
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(This article belongs to the Special Issue Recent Advances in Quantum Cosmology)
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