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
Measuring the Lense–Thirring Precession and the Neutron Star Moment of Inertia with Pulsars
Universe 2024, 10(4), 160; https://doi.org/10.3390/universe10040160 - 28 Mar 2024
Abstract
Neutron stars (NSs) are compact objects that host the densest forms of matter in the observable universe, providing unique opportunities to study the behaviour of matter at extreme densities. While precision measurements of NS masses through pulsar timing have imposed effective constraints on
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Neutron stars (NSs) are compact objects that host the densest forms of matter in the observable universe, providing unique opportunities to study the behaviour of matter at extreme densities. While precision measurements of NS masses through pulsar timing have imposed effective constraints on the equation of state (EoS) of dense matter, accurately determining the radius or moment of inertia (MoI) of an NS remains a major challenge. This article presents a detailed review on measuring the Lense–Thirring (LT) precession effect in the orbit of binary pulsars, which would give access to the MoI of NSs and offer further constraints on the EoS. We discuss the suitability of certain classes of binary pulsars for measuring the LT precession from the perspective of binary star evolution and highlight five pulsars that exhibit properties promising to realise these goals in the near future. Finally, discoveries of compact binaries with shorter orbital periods hold the potential to greatly enhance measurements of the MoI of NSs. The MoI measurements of binary pulsars are pivotal to advancing our understanding of matter at supranuclear densities, as well as improving the precision of gravity tests, such as the orbital decay due to gravitational wave emission, and of tests of alternative gravity theories.
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(This article belongs to the Special Issue Studies in Neutron Stars)
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Boyer–Lindquist Space-Times and Beyond: Metamaterial Analogues for ArbitrarySpace-Times
by
Sebastian Schuster and Matt Visser
Universe 2024, 10(4), 159; https://doi.org/10.3390/universe10040159 - 28 Mar 2024
Abstract
Analogue space-times (and in particular metamaterial analogue space-times) have a long varied and rather complex history. Much of the previous related work to this field has focused on spherically symmetric models; however, axial symmetry is much more relevant for mimicking astrophysically interesting systems
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Analogue space-times (and in particular metamaterial analogue space-times) have a long varied and rather complex history. Much of the previous related work to this field has focused on spherically symmetric models; however, axial symmetry is much more relevant for mimicking astrophysically interesting systems that are typically subject to rotation. Now it is well known that physically reasonable stationary axisymmetric space-times can, under very mild technical conditions, be put into Boyer–Lindquist form. Unfortunately, a metric presented in Boyer–Lindquist form is not well adapted to the “quasi-Cartesian” metamaterial analysis that we developed in our previous articles on “bespoke analogue space-times”. In the current article, we shall first focus specifically on various space-time metrics presented in Boyer–Lindquist form, and subsequently determine a suitable set of equivalent metamaterial susceptibility tensors in a laboratory setting. We shall then turn to analyzing generic space-times, not even necessarily stationary, again determining a suitable set of equivalent metamaterial susceptibility tensors. Perhaps surprisingly, we find that the well-known ADM formalism proves to be not particularly useful, and that it is instead the dual “threaded” (Kaluza–Klein–inspired) formalism that provides much more tractable results. While the background laboratory metric is (for mathematical simplicity and physical plausibility) always taken to be Riemann flat, we will allow for arbitrary curvilinear coordinate systems on the flat background space-time. Finally, for completeness, we shall reconsider spherically symmetric space-times, but now in general spherical polar coordinates rather than quasi-Cartesian coordinates. In summary, this article provides a set of general-purpose calculational tools that can readily be adapted for mimicking various interesting (curved) space-times by using nontrivial susceptibility tensors in general (background-flat) laboratory settings.
Full article
(This article belongs to the Special Issue Analogue Gravity)
Open AccessReview
A Needle in a Cosmic Haystack: A Review of FRB Search Techniques
by
Kaustubh M. Rajwade and Joeri van Leeuwen
Universe 2024, 10(4), 158; https://doi.org/10.3390/universe10040158 - 28 Mar 2024
Abstract
Ephemeral Fast Radio Bursts (FRBs) must be powered by some of the most energetic processes in the Universe. That makes them highly interesting in their own right, and as precise probes for estimating cosmological parameters. This field thus poses a unique challenge: FRBs
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Ephemeral Fast Radio Bursts (FRBs) must be powered by some of the most energetic processes in the Universe. That makes them highly interesting in their own right, and as precise probes for estimating cosmological parameters. This field thus poses a unique challenge: FRBs must be detected promptly and immediately localised and studied based only on that single millisecond-duration flash. The problem is that the burst occurrence is highly unpredictable and that their distance strongly suppresses their brightness. Since the discovery of FRBs in single-dish archival data in 2007, detection software has evolved tremendously. Pipelines now detect bursts in real time within a matter of seconds, operate on interferometers, buffer high-time and frequency resolution data, and issue real-time alerts to other observatories for rapid multi-wavelength follow-up. In this paper, we review the components that comprise a FRB search software pipeline, we discuss the proven techniques that were adopted from pulsar searches, we highlight newer, more efficient techniques for detecting FRBs, and we conclude by discussing the proposed novel future methodologies that may power the search for FRBs in the era of big data astronomy.
Full article
(This article belongs to the Special Issue New Insights in Fast Radio Bursts)
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Asteroseismology of Compact Stars
by
Hong-Bo Li, Yong Gao, Lijing Shao and Ren-Xin Xu
Universe 2024, 10(4), 157; https://doi.org/10.3390/universe10040157 - 27 Mar 2024
Abstract
Compact stars have been perceived as natural laboratories of matter at an extremely high density. The uncertainties of the equation of state (EOS) of matter can be constrained by observing compact stars. In this review, we investigate the EOSs, global structure, and elastic
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Compact stars have been perceived as natural laboratories of matter at an extremely high density. The uncertainties of the equation of state (EOS) of matter can be constrained by observing compact stars. In this review, we investigate the EOSs, global structure, and elastic properties of compact stars. We focus in detail on how to constrain the above properties of compact stars via asteroseismology. Observations that include studies of quasi-periodic oscillations from giant flares of soft gamma-ray repeaters and gravitational waves provide information about the elastic properties and internal compositions of compact stars.
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(This article belongs to the Special Issue Pulsar Astronomy)
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The Power of Relativistic Jets: A Comparative Study
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Luigi Foschini, Benedetta Dalla Barba, Merja Tornikoski, Heinz Andernach, Paola Marziani, Alan P. Marscher, Svetlana G. Jorstad, Emilia Järvelä, Sonia Antón and Elena Dalla Bontà
Universe 2024, 10(4), 156; https://doi.org/10.3390/universe10040156 (registering DOI) - 27 Mar 2024
Abstract
We present the results of a comparison between different methods to estimate the power of relativistic jets from active galactic nuclei (AGN). We selected a sample of 32 objects (21 flat-spectrum radio quasars, 7 BL Lacertae objects, 2 misaligned AGN, and 2 changing-look
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We present the results of a comparison between different methods to estimate the power of relativistic jets from active galactic nuclei (AGN). We selected a sample of 32 objects (21 flat-spectrum radio quasars, 7 BL Lacertae objects, 2 misaligned AGN, and 2 changing-look AGN) from the very large baseline array (VLBA) observations at 43 GHz of the Boston University blazar program. We then calculated the total, radiative, and kinetic jet power from both radio and high-energy gamma-ray observations, and compared the values. We found an excellent agreement between the radiative power calculated by using the Blandford and Königl model with 37 or 43 GHz data and the values derived from the high-energy -ray luminosity. The agreement is still acceptable if 15 GHz data are used, although with a larger dispersion, but it improves if we use a constant fraction of the -ray luminosity. We found a good agreement also for the kinetic power calculated with the Blandford and Königl model with 15 GHz data and the value from the extended radio emission. We also propose some easy-to-use equations to estimate the jet power.
Full article
(This article belongs to the Special Issue Recent Advances in Gamma Ray Astrophysics and Future Perspectives)
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Open AccessArticle
Tracking Dusty Cloud Crushed by a Hot Flow
by
Svyatoslav Dedikov and Evgenii Vasiliev
Universe 2024, 10(4), 155; https://doi.org/10.3390/universe10040155 (registering DOI) - 26 Mar 2024
Abstract
The destructionof clouds by strong shocks and hot winds is the key process responsible for the transporting of metals and dust from the ISM to the ICM/IGM, and establishing the multiphase structure in and around galaxies. In this work, we perform a detailed
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The destructionof clouds by strong shocks and hot winds is the key process responsible for the transporting of metals and dust from the ISM to the ICM/IGM, and establishing the multiphase structure in and around galaxies. In this work, we perform a detailed analysis of this process using two different approaches for tracking the cloud material (gas and dust): the so-called ‘colored’ fluid, and the Lagrangian (trace) particles. We find that for the clouds in the hot phase ( K), the two methods produce significantly different mass fractions and velocities of the cloud material. In contrast, the two methods produce similar results for the clouds that are in the warm/cold phases ( K). We find that the Kelvin–Helmholtz instability is suppressed in the warm clouds of size ∼100 pc and metallicity Z> 0.1Z
Full article
(This article belongs to the Special Issue High Energy Emission from Clusters, Groups, and Filaments: Current Observations and Future Prospects)
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Open AccessArticle
Jets Studies in Central and Forward Regions at Current and Expected Large Hadron Collider Future Energies
by
M. A. Mahmoud, Somaia Hamdi, A. Radi, M. A. El-Borie and E. A. Tayel
Universe 2024, 10(4), 154; https://doi.org/10.3390/universe10040154 - 25 Mar 2024
Abstract
The present work presents a study of jet production in the central region ( < 2.5) and the forward region (3 < < 5) in proton–proton collisions at different energies: = 13.6 TeV, = 20
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The present work presents a study of jet production in the central region ( < 2.5) and the forward region (3 < < 5) in proton–proton collisions at different energies: = 13.6 TeV, = 20 TeV, and = 27 TeV. These energies are the present and expected future energies of the Large Hadron Collider. In addition, the measurement of dijets—where the dijet selected is the one leading the jet in the central region and the second jet is the one with the sub-leading role in the forward region—was investigated with the same collision energies. Jets are reconstructed with the anti-kT (R = 0.5) algorithm in the transverse momentum range pT = 15–1000 GeV/c. Different Monte Carlo event generators were used: PYTHIA, HERWIG, and EPOS-LHC. The momentum, multiplicity, energy, pseudorapidity, and azimuthal angle of the jets were measured. In addition, the dijet multiplicity and the difference in the azimuthal angle were measured. The generation of events was carried out using the Rivet analysis framework. It is observed that, when the energy of the collision increases, the production of the jets in the central and forward regions and the dijets multiplicity increase; overall an agreement is observed between the three event generators. The disagreement between the different generators points to potential areas for development or additional study.
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(This article belongs to the Section High Energy Nuclear and Particle Physics)
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Open AccessReview
Scientific Highlights of the AGILE Gamma-ray Mission
by
Stefano Vercellone, Carlotta Pittori and Marco Tavani
Universe 2024, 10(4), 153; https://doi.org/10.3390/universe10040153 - 25 Mar 2024
Abstract
The -ray sky above a few tens of megaelectronvolts (MeV) reveals some of the most powerful and energetic phenomena of our Universe. The Astrorivelatore Gamma ad Immagini LEggero (AGILE) Gamma-ray Mission was launched in 2007 with the aim of observing celestial sources
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The -ray sky above a few tens of megaelectronvolts (MeV) reveals some of the most powerful and energetic phenomena of our Universe. The Astrorivelatore Gamma ad Immagini LEggero (AGILE) Gamma-ray Mission was launched in 2007 with the aim of observing celestial sources by means of three instruments covering a wide range of energies, from hard X-rays up to 30 GeV. Thanks to its wide field of view, AGILE set to observe and detect emission from pulsars, pulsar wind nebulae, gamma-ray bursts, active galactic nuclei, fast radio bursts, terrestrial gamma-ray flashes, and the electromagnetic counterparts of neutrinos and gravitational waves. In particular, the fast on-ground processing and analysis chain allowed the AGILE team to promptly respond to transient events, and activate or participate in multiwavelength observing campaigns. Eventually, after 17 years of operations, the AGILE Italian scientific satellite re-entered the atmosphere on 14 February 2024, ending its intense activity as a hunter of some of the most energetic cosmic sources in the Universe that emit X and -rays. We will review the most relevant AGILE results to date and their impact on the advancements of theoretical models.
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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 Shock Cone Instabilities and Quasi-Periodic Oscillations around the Hartle–Thorne Black Hole
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Orhan Donmez and Fatih Dogan
Universe 2024, 10(4), 152; https://doi.org/10.3390/universe10040152 - 24 Mar 2024
Abstract
To explain the observed X-ray data in a black hole–accreting matter system and understand the physical mechanisms behind QPOs, we have numerically modeled the dynamical and oscillation properties of the shock cone formed around both slowly and rapidly rotating Hartle–Thorne black holes, resulting
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To explain the observed X-ray data in a black hole–accreting matter system and understand the physical mechanisms behind QPOs, we have numerically modeled the dynamical and oscillation properties of the shock cone formed around both slowly and rapidly rotating Hartle–Thorne black holes, resulting from the mechanism of Bondi–Hoyle–Lyttleton (BHL). According to the numerical simulations, an increase in the quadrupole parameter leads to a decrease in the shock cone opening angle around the black hole. A larger quadrupole parameter results in more matter falling into the black hole within the cone. The combination of the quadrupole parameter and black hole rotation causes the matter inside the cone to exhibit chaotic motion. These dynamical changes and chaotic behavior of the shock cones excite the fundamental oscillation modes. Moreover, new frequencies have been formed due to the nonlinear coupling of the fundamental modes. Conversely, we have numerically studied the behavior of cones formed around rapidly rotating Hartle–Thorne black holes and found differences and similarities to those obtained from slowly rotating cases. Finally, comparing the outcomes obtained fromHartle–Thorne gravity with the results fromKerr and Einstein–Gauss–Bonnet (EGB) gravities reveals the impact of the quadrupole parameter on the shock cone and QPOs.
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(This article belongs to the Section Compact Objects)
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The κ-Model under the Test of the SPARC Database
by
Gianni Pascoli
Universe 2024, 10(3), 151; https://doi.org/10.3390/universe10030151 - 21 Mar 2024
Abstract
Our main goal here is to conduct a comparative analysis between the well-known MOND theory and a more recent model called the -model. An additional connection, between the -model and two other novel MOND-type theories, Newtonian Fractional-Dimension Gravity (NFDG) and Refracted
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Our main goal here is to conduct a comparative analysis between the well-known MOND theory and a more recent model called the -model. An additional connection, between the -model and two other novel MOND-type theories, Newtonian Fractional-Dimension Gravity (NFDG) and Refracted Gravity (RG), is likewise presented. All these models are built to overtake the DM paradigm, or at least to strongly reduce the dark matter content. Whereas they rely on different formalisms, however, all four seem to suggest that the universal parameter, , appearing in MOND theory could intrinsically be correlated to either the sole baryonic mean mass density (RG and -model) and/or to the dimension of the object under consideration (NFDG and -model). We then confer to parameter a more flexible status of multiscale parameter, as required to explain the dynamics together in galaxies and in galaxy clusters. Eventually, the conformal gravity theory (CFT) also seems to have some remote link with the -model, even though the first one is an extension of general relativity, and the second one is Newtonian in essence. The -model has been tested on a small sample of spiral galaxies and in galaxy clusters. Now, we test this model on a large sample of galaxies issued from the SPARC database.
Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")
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Emergent Spacetime and Cosmic Inflation
by
Hyun Seok Yang
Universe 2024, 10(3), 150; https://doi.org/10.3390/universe10030150 - 21 Mar 2024
Abstract
We present a novel background-independent framework for cosmic inflation, starting with a matrix model. In this framework, inflation is portrayed as a dynamic process responsible for the generation of both space and time. This stands in contrast to conventional inflation, which is characterized
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We present a novel background-independent framework for cosmic inflation, starting with a matrix model. In this framework, inflation is portrayed as a dynamic process responsible for the generation of both space and time. This stands in contrast to conventional inflation, which is characterized as a mere (exponential) expansion of an already existing spacetime, driven by the vacuum energy associated with an inflaton field. We observe that the cosmic inflation is triggered by the condensate of Planck energy into a vacuum and responsible for the dynamical emergence of spacetime. The emergent spacetime picture admits a background-independent formulation so that the inflation is described by a conformal Hamiltonian system which requires neither an inflaton field nor an ad hoc inflation potential. This implies that the emergent spacetime may incapacitate all the rationales to introduce the multiverse hypothesis.
Full article
(This article belongs to the Special Issue Mathematical Cosmology)
Open AccessReview
High-Energy and Ultra-High-Energy Neutrino Astrophysics
by
Damiano F. G. Fiorillo
Universe 2024, 10(3), 149; https://doi.org/10.3390/universe10030149 - 20 Mar 2024
Abstract
The origin of high-energy cosmic rays, and their behavior in astrophysical sources, remains an open question. Recently, new ways to address this question have been made possible by the observation of a new astrophysical messenger, namely neutrinos. The IceCube telescope has detected a
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The origin of high-energy cosmic rays, and their behavior in astrophysical sources, remains an open question. Recently, new ways to address this question have been made possible by the observation of a new astrophysical messenger, namely neutrinos. The IceCube telescope has detected a diffuse flux of astrophysical neutrinos in the TeV-PeV energy range, likely produced in astrophysical sources accelerating cosmic rays, and more recently it has reported on a few candidate individual neutrino sources. Future experiments will be able to improve on these measurements quantitatively, by the detection of more events, and qualitatively, by extending the measurement into the EeV energy range. In this paper, we review the main features of the neutrino emission and sources observed by IceCube, as well as the main candidate sources that could contribute to the diffuse neutrino flux. As a parallel question, we review the status of high-energy neutrinos as a probe of Beyond the Standard Model physics coupling to the neutrino sector.
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(This article belongs to the Special Issue Neutrinos across Different Energy Scales)
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Open AccessReview
The Physics of Core-Collapse Supernovae: Explosion Mechanism and Explosive Nucleosynthesis
by
Luca Boccioli and Lorenzo Roberti
Universe 2024, 10(3), 148; https://doi.org/10.3390/universe10030148 - 19 Mar 2024
Abstract
Recent developments in multi-dimensional simulations of core-collapse supernovae have considerably improved our understanding of this complex phenomenon. In addition to that, one-dimensional (1D) studies have been employed to study the explosion mechanism and its causal connection to the pre-collapse structure of the star,
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Recent developments in multi-dimensional simulations of core-collapse supernovae have considerably improved our understanding of this complex phenomenon. In addition to that, one-dimensional (1D) studies have been employed to study the explosion mechanism and its causal connection to the pre-collapse structure of the star, as well as to explore the vast parameter space of supernovae. Nonetheless, many uncertainties still affect the late stages of the evolution of massive stars, their collapse, and the subsequent shock propagation. In this review, we will briefly summarize the state-of-the-art of both 1D and 3D simulations and how they can be employed to study the evolution of massive stars, supernova explosions, and shock propagation, focusing on the uncertainties that affect each of these phases. Finally, we will illustrate the typical nucleosynthesis products that emerge from the explosion.
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(This article belongs to the Special Issue Recent Outcomes and Future Challenges in Nuclear Astrophysics)
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Open AccessArticle
Conformally Invariant Gravity and Gravitating Mirages
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Victor Berezin and Inna Ivanova
Universe 2024, 10(3), 147; https://doi.org/10.3390/universe10030147 - 17 Mar 2024
Abstract
The action of an ideal fluid in Euler variables with a variable number of particles is used for the phenomenological description of the processes of particle creation in strong external fields. It has been demonstrated that the conformal invariance of the creation law
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The action of an ideal fluid in Euler variables with a variable number of particles is used for the phenomenological description of the processes of particle creation in strong external fields. It has been demonstrated that the conformal invariance of the creation law imposes quite strict restrictions on the possible types of sources. It is shown that combinations with the particle number density in the creation law can be interpreted as dark matter within the framework of this model.
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(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)
Open AccessReview
The ASTRI Mini-Array: A New Pathfinder for Imaging Cherenkov Telescope Arrays
by
Salvatore Scuderi
Universe 2024, 10(3), 146; https://doi.org/10.3390/universe10030146 - 16 Mar 2024
Abstract
The ASTRI Mini-Array is an Istituto Nazionale di Astrofisica (INAF) project to build and operate an array of nine Imaging Atmospheric Cherenkov Telescopes (IACTs) at the Teide Astronomical Observatory of the Instituto de Astrofisica de Canarias in Tenerife (Spain) based on a host
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The ASTRI Mini-Array is an Istituto Nazionale di Astrofisica (INAF) project to build and operate an array of nine Imaging Atmospheric Cherenkov Telescopes (IACTs) at the Teide Astronomical Observatory of the Instituto de Astrofisica de Canarias in Tenerife (Spain) based on a host agreement with INAF and, as such, it will be the largest IACT array until the Cherenkov Telescope Array Observatory starts operations. Implementing the ASTRI Mini-Array poses several challenges from technical, logistic, and management points of view. Starting from the description of the innovative technologies adopted to build the telescopes, we will discuss the solutions adopted to overcome these challenges, making the ASTRI Mini-Array a great instrument to perform deep observations of the galactic and extra-galactic sky at very high energies.
Full article
(This article belongs to the Special Issue Recent Advances in Gamma Ray Astrophysics and Future Perspectives)
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Multiple SSO Space Debris Flyby Trajectory Design Based on Cislunar Orbit
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Siyang Zhang and Shuquan Wang
Universe 2024, 10(3), 145; https://doi.org/10.3390/universe10030145 - 16 Mar 2024
Abstract
This paper investigates the trajectory design problem in the scenario of a multiple Sun-synchronous Orbit (SSO) space debris flyby mission from a DRO space station. At first, the characteristics of non-planar transfer from DRO to SSO in the Earth–Moon system are analyzed. The
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This paper investigates the trajectory design problem in the scenario of a multiple Sun-synchronous Orbit (SSO) space debris flyby mission from a DRO space station. At first, the characteristics of non-planar transfer from DRO to SSO in the Earth–Moon system are analyzed. The methods of large-scale ergodicity and pruning are utilized to investigate single-impulse and two-impulse DRO–Earth transfers. Using a powered lunar flyby, the two-impulse DRO–Earth transfer is able to fly by SSO debris while satisfying the requirements of the mission. After the local optimization, the optimal result of two-impulse DRO–Earth transfer and flyby is obtained. A multi-objective evolutionary algorithm is used to design the Pareto-optimal trajectories of multiple flybys. The semi-analytical optimization method is developed to provide the estimations of the transfer parameters in order to reduce the computations caused by the evolutionary algorithm. Simulations show that transferring from the 3:2 resonant DRO to a near-coplanar flyby of a SSO target debris using a powered lunar gravity assist needs a 0.47 km/s velocity increment. The mission’s total velocity increment is 1.39 km/s, and the total transfer time is 2.23 years.
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(This article belongs to the Topic Techniques and Science Exploitations for Earth Observation and Planetary Exploration)
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Open AccessEditorial
Origins and Natures of Inflation, Dark Matter and Dark Energy
by
Kazuharu Bamba
Universe 2024, 10(3), 144; https://doi.org/10.3390/universe10030144 - 15 Mar 2024
Abstract
Various precise cosmological observations, e [...]
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(This article belongs to the Special Issue Origins and Natures of Inflation, Dark Matter and Dark Energy)
Open AccessArticle
The Relevance of Dynamical Friction for the MW/LMC/SMC Triple System
by
Wolfgang Oehm and Pavel Kroupa
Universe 2024, 10(3), 143; https://doi.org/10.3390/universe10030143 - 14 Mar 2024
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Simulations of structure formation in the standard cold dark matter cosmological model quantify the dark matter halos of galaxies. Taking into account dynamical friction between dark matter halos, we investigate the past orbital dynamical evolution of the Magellanic Clouds in the presence of
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Simulations of structure formation in the standard cold dark matter cosmological model quantify the dark matter halos of galaxies. Taking into account dynamical friction between dark matter halos, we investigate the past orbital dynamical evolution of the Magellanic Clouds in the presence of the Galaxy. Our calculations are based on a three-body model of rigid Navarro–Frenk–White profiles for dark matter halos but were verified in a previous publication by comparison to high-resolution N-body simulations of live self-consistent systems. Under the requirement that the LMC and SMC had an encounter within 20 kpc between 1 and 4 Gyr ago in order to allow the development of the Magellanic Stream, using the latest astrometric data, the dynamical evolution of the MW/LMC/SMC system is calculated backwards in time. With the employment of the genetic algorithm and a Markov-Chain Monte-Carlo method, the present state of this system is unlikely, with a probability of ( complement), because the solutions found do not fit into the error bars for the observed plane-of-sky velocity components of the Magellanic Clouds. This implies that orbital solutions that assume dark matter halos, according to cosmological structure formation theory, to exist around the Magellanic Clouds and the Milky Way are not possible with a confidence of more than 6 sigma.
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Open AccessArticle
On the Apparent Discretization of Spacetime and Its Connection with the Cosmological Constant
by
Jaume Giné and Giuseppe Gaetano Luciano
Universe 2024, 10(3), 142; https://doi.org/10.3390/universe10030142 - 14 Mar 2024
Abstract
The emergence of a minimal observable length of order of the Planck scale is a prediction of many quantum theories of gravity. However, the question arises as to whether this is a real fundamental length affecting nature in all of its facets, including
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The emergence of a minimal observable length of order of the Planck scale is a prediction of many quantum theories of gravity. However, the question arises as to whether this is a real fundamental length affecting nature in all of its facets, including spacetime. In this work, we show that the quantum measurement process implies the existence of a minimal measurable length and consequently the apparent discretization of spacetime. The obtained result is used to infer the value of zero-point energy in the universe, which is found to be in good agreement with the observed cosmological constant. This potentially offers some hints towards the resolution of the cosmological constant problem.
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(This article belongs to the Section Foundations of Quantum Mechanics and Quantum Gravity)
Open AccessArticle
Constraining the Initial Mass Function in the Epoch of Reionization from Astrophysical and Cosmological Data
by
Andrea Lapi, Giovanni Gandolfi, Lumen Boco, Francesco Gabrielli, Marcella Massardi, Balakrishna S. Haridasu, Carlo Baccigalupi, Alessandro Bressan and Luigi Danese
Universe 2024, 10(3), 141; https://doi.org/10.3390/universe10030141 - 13 Mar 2024
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We aim to constrain the stellar initial mass function (IMF) during the epoch of reionization. To this purpose, we build up a semi-empirical model for the reionization history of the Universe based on various ingredients: the latest determination of the UV galaxy luminosity
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We aim to constrain the stellar initial mass function (IMF) during the epoch of reionization. To this purpose, we build up a semi-empirical model for the reionization history of the Universe based on various ingredients: the latest determination of the UV galaxy luminosity function from JWST out to redshift ; data-inferred and simulation-driven assumptions on the redshift-dependent escape fraction of ionizing photons from primordial galaxies; a simple yet flexible parameterization of the IMF ∼ in terms of a high-mass end slope and a characteristic mass , below which a flattening or a bending sets in (allowing description of a variety of IMF shapes from the classic Salpeter to top-heavy ones); the PARSEC stellar evolution code to compute the UV and ionizing emission from different stars’ masses as a function of age and metallicity; and a few physical constraints related to stellar and galaxy formation in faint galaxies at the reionization redshifts. We then compare our model outcomes with the reionization observables from different astrophysical and cosmological probes and perform Bayesian inference on the IMF parameters via a standard MCMC technique. We find that the IMF slope is within the range from to , consistent with direct determination from star counts in the Milky Way, while appreciably flatter slopes are excluded at great significance. However, the bestfit value of the IMF characteristic mass ∼a few implies a suppression in the formation of small stellar masses at variance with the IMF in the local Universe. This may be induced by the thermal background of ∼20–30 K provided by CMB photons at the reionization redshifts. We check that our results are robust against different parameterizations for the redshift evolution of the escape fraction. Finally, we investigate the implications of our reconstructed IMF for the recent JWST detections of massive galaxies at and beyond the reionization epoch, showing that any putative tension with the standard cosmological framework is substantially alleviated.
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