Universe

15 pages, 1888 KiB

Open AccessReview

Direct and Indirect Measurements of the ¹⁹F(p,α)¹⁶O Reaction at Astrophysical Energies Using the LHASA Detector and the Trojan Horse Method

by Giovanni L. Guardo, Giuseppe G. Rapisarda, Dimiter L. Balabanski, Giuseppe D’Agata, Alessia Di Pietro, Pierpaolo Figuera, Marco La Cognata, Marco La Commara, Livio Lamia, Dario Lattuada, Catalin Matei, Marco Mazzocco, Alessandro A. Oliva, Sara Palmerini, Teodora Petruse, Rosario G. Pizzone, Stefano Romano, Maria Letizia Sergi, Roberta Spartá, Xuedou Su, Aurora Tumino and Nikola Vukman Show full author list Hide full author list

Universe 2024, 10(7), 304; https://doi.org/10.3390/universe10070304 - 22 Jul 2024

Cited by 1 | Viewed by 772

Abstract

Fluorine is one of the most interesting elements in nuclear astrophysics. Its abundance can provide important hints to constrain the stellar models since fluorine production and destruction are strictly connected to the physical conditions inside the stars. The

{}^{19}F

(p,α)¹⁶O [...] Read more.

Fluorine is one of the most interesting elements in nuclear astrophysics. Its abundance can provide important hints to constrain the stellar models since fluorine production and destruction are strictly connected to the physical conditions inside the stars. The

{}^{19}F

(p,α)¹⁶O reaction is one of the fluorine burning processes and the correction evaluation of its reaction rate is of pivotal importance to evaluate the fluorine abundance. Moreover, the

{}^{19}F

(p,α)¹⁶O reaction rate can have an impact for the production of calcium in the first-generation of Population III stars. Here, we present the AsFiN collaboration efforts to the study of the

{}^{19}F

(p,

α

)¹⁶O reaction by means of direct and indirect measurements. On the direct measurements side, an experimental campaign aimed to the measurement of the

{}^{19}F

(p,

α_{0, π}

)¹⁶O reaction is ongoing, taking advantage of the new versatile arrays of silicon strip detectors, LHASA and ELISSA. Moreover, the Trojan Horse Method (THM) was used to determine the

{}^{19}F

(p,

α_{0}

)¹⁶O reaction S(E)-factor in the energy range of astrophysical interest (

E_{c m}

≈ 0–1 MeV), showing, for the first time, the presence of resonant structures within the astrophysical energy range. THM has been also applied for the study of the

{}^{19}F

(p,

α_{π}

)¹⁶O reaction; data analysis is ongoing. Full article

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

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16 pages, 600 KiB

Open AccessReview

Dissipative Kinematics in Binary Neutron Star Mergers

by Sreemoyee Sarkar and Souvik Priyam Adhya

Universe 2024, 10(7), 303; https://doi.org/10.3390/universe10070303 - 22 Jul 2024

Viewed by 700

Abstract

We highlight the recent progress in the calculation of transport coefficients pertinent to binary neutron star mergers. Specifically, we analyze the bulk viscosity coefficient driven by both the DURCA and MURCA processes and electron transport coefficients in dense and hot plasma relevant to [...] Read more.

We highlight the recent progress in the calculation of transport coefficients pertinent to binary neutron star mergers. Specifically, we analyze the bulk viscosity coefficient driven by both the DURCA and MURCA processes and electron transport coefficients in dense and hot plasma relevant to the merger scenario. The study considers high temperatures (

T > 6 \times 10^{10}

K) and dense environments (

n_{B} \sim n_{0} - 3 n_{0}

). Bulk viscosity exhibits resonant behavior, with peak values and peak positions dependent on particle interaction rates and thermodynamic susceptibilities. Susceptibilities are calculated by modeling the nuclear matter in the density functional approach. The bulk viscosity coefficient peaks at

T \sim 10^{11}

K, with a compression–rarefaction oscillation dissipation time scale of 20–50 ms. Electrical transports incorporate frequency-dependent dynamical screening in quantized electron–ion scattering rates. Consequently, dynamical screening reduces the maxima of electrical and thermal conductivities, shortening corresponding dissipation time scales. These results highlight the crucial role of dissipation coefficients in understanding binary neutron star mergers. Full article

(This article belongs to the Special Issue Exploring Quark Matter under Extreme Scenarios of Temperature and Density)

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12 pages, 887 KiB

Open AccessArticle

Nonlinear Dynamics in Variable-Vacuum Finsler–Randers Cosmology with Triple Interacting Fluids

by Jianwen Liu, Ruifang Wang and Fabao Gao

Universe 2024, 10(7), 302; https://doi.org/10.3390/universe10070302 - 21 Jul 2024

Viewed by 726

Abstract

Considering the interaction among matter, vacuum, and radiation, this paper investigates the evolution of cosmic dynamics of the varying-vacuum model in a case of Finslerian geometry through dynamic analysis methods. Surprisingly, this model can alleviate the coincidence problem and allows for a stable [...] Read more.

Considering the interaction among matter, vacuum, and radiation, this paper investigates the evolution of cosmic dynamics of the varying-vacuum model in a case of Finslerian geometry through dynamic analysis methods. Surprisingly, this model can alleviate the coincidence problem and allows for a stable later cosmological solution corresponding to the accelerating universe. Full article

(This article belongs to the Section Cosmology)

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10 pages, 267 KiB

Open AccessArticle

Estimate for the Neutrino Magnetic Moment from Pulsar Kick Velocities Induced at the Birth of Strange Quark Matter Neutron Stars

by Alejandro Ayala, Santiago Bernal-Langarica and Daryel Manreza-Paret

Universe 2024, 10(7), 301; https://doi.org/10.3390/universe10070301 - 20 Jul 2024

Viewed by 832

Abstract

We estimate the magnetic moment of electron neutrinos by computing the neutrino chirality flip rate that can occur in the core of a strange quark matter neutron star at birth. We show that this process allows neutrinos to anisotropically escape, thus inducing the [...] Read more.

We estimate the magnetic moment of electron neutrinos by computing the neutrino chirality flip rate that can occur in the core of a strange quark matter neutron star at birth. We show that this process allows neutrinos to anisotropically escape, thus inducing the star kick velocity. Although the flip from left- to right-handed neutrinos is assumed to happen in equilibrium, the no-go theorem does not apply because right-handed neutrinos do not interact with matter and the reverse process does not happen, producing the loss of detailed balance. For simplicity, we model the star core as consisting of strange quark matter. We find that even when the energy released in right-handed neutrinos is a small fraction of the total energy released in left-handed neutrinos, the process describes kick velocities for natal conditions, which are consistent with the observed ones and span the correct range of radii, temperatures and chemical potentials for typical magnetic field intensities. The neutrino magnetic moment is estimated to be

μ_{ν} \sim 3.6 \times 10^{- 18} μ_{B}

, where

μ_{B}

is the Bohr magneton. This value is more stringent than the bound found for massive neutrinos in a minimal extension of the standard model. Full article

(This article belongs to the Special Issue Studies in Neutron Stars)

9 pages, 2120 KiB

Open AccessArticle

Study of Wide-Field-of-View X-ray Observations of the Virgo Cluster Using the Lobster Eye Imager for Astronomy

by Wen-Cheng Feng, Shu-Mei Jia, Hai-Hui Zhao, Heng Yu, Hai-Wu Pan, Cheng-Kui Li, Yu-Lin Cheng, Shan-Shan Weng, Yong Chen, Yuan Liu, Zhi-Xing Ling and Chen Zhang

Universe 2024, 10(7), 300; https://doi.org/10.3390/universe10070300 - 17 Jul 2024

Viewed by 751

Abstract

The Lobster Eye Imager for Astronomy (LEIA) is the pathfinder of the wide-field X-ray telescope used in the Einstein Probe mission. In this study, we present an image of the Virgo Cluster taken by LEIA in the 0.5–4.5 keV band with an exposure [...] Read more.

The Lobster Eye Imager for Astronomy (LEIA) is the pathfinder of the wide-field X-ray telescope used in the Einstein Probe mission. In this study, we present an image of the Virgo Cluster taken by LEIA in the 0.5–4.5 keV band with an exposure time of ∼17.3 ks in the central region. This extended emission is generally consistent with the results obtained by ROSAT. However, the field is affected by bright point sources due to the instrument’s Point Spread Function (PSF) effect. Through fitting of the LEIA spectrum of the Virgo Cluster, we obtained a temperature of

2 . 1_{- 0.1}^{+ 0.3}

keV, which is consistent with the XMM-Newton results (∼2.3 keV). Above 1.6 keV, the spectrum is dominated by the X-ray background. In summary, this study validates LEIA’s extended source imaging and spectral resolution capabilities for the first time. Full article

(This article belongs to the Section Galaxies and Clusters)

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20 pages, 677 KiB

Open AccessArticle

Location Problem in Relativistic Positioning: Relative Formulation

by Ramón Serrano Montesinos, Joan Josep Ferrando and Juan Antonio Morales-Lladosa

Universe 2024, 10(7), 299; https://doi.org/10.3390/universe10070299 - 17 Jul 2024

Viewed by 572

Abstract

A relativistic positioning system is a set of four emitters broadcasting their proper times by means of light signals. The four emitter times received at an event constitute the emission coordinates of the event. The covariant quantities associated with relativistic positioning systems are [...] Read more.

A relativistic positioning system is a set of four emitters broadcasting their proper times by means of light signals. The four emitter times received at an event constitute the emission coordinates of the event. The covariant quantities associated with relativistic positioning systems are analysed relative to an observer in Minkowski space-time by splitting them in their relative space-like and time-like components. The location of a user in inertial coordinates from a standard set of emission data (emitted times and satellite trajectories) is solved in the underlying 3+1 formalism. The analytical location solution obtained by Kleusberg for the GPS system is recovered and interpreted in a Minkowskian context. Full article

(This article belongs to the Section Gravitation)

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21 pages, 784 KiB

Open AccessArticle

Soft X-ray Spectrum Changes over the 35-Day Cycle in Hercules X-1 Observed with AstroSat SXT

by Denis Leahy and Riddhiman Sharma

Universe 2024, 10(7), 298; https://doi.org/10.3390/universe10070298 - 15 Jul 2024

Viewed by 832

Abstract

Observations of the X-ray binary system Her X-1 by the AstroSat Soft X-ray Telescope (SXT) were carried out in 2020 through 2023 with the goals of measuring X-ray spectrum changes with the 35-day disk precession phase and measuring eclipses at different 35-day phases. [...] Read more.

Observations of the X-ray binary system Her X-1 by the AstroSat Soft X-ray Telescope (SXT) were carried out in 2020 through 2023 with the goals of measuring X-ray spectrum changes with the 35-day disk precession phase and measuring eclipses at different 35-day phases. Her X-1 exhibits a regular flux modulation with a period of ≃35 days with different intensity levels at various 35-day phases (called “states”). The four multi-day long observations were scheduled to cover most of these states. Each 35-day phase was determined using monitoring observations with the Swift Burst Alert Telescope (BAT). Nine eclipses were observed in the range of 35-day phases, with at least one eclipse during each observation. Data with dips were separated from data without dips. The variation in X-ray spectral parameters vs. 35-day phase shows the following: eclipse parameters are nearly constant, showing that the scattering corona does not change with 35-day phase; dips show an increase in covering fraction but not column density compared to non-dip data; the1 keV line normalization behaves similarly to the powerlaw normalization, consistent with an origin near the powerlaw emission region, likely the magnetospheric accretion flow from the inner disk onto the neutron star; and the blackbody normalization (area) is large (

\sim 3 \times 10^{5}

km²) during the Main High and Short High states, consistent with the inner edge of the accretion disk. Full article

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

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15 pages, 1096 KiB

Open AccessArticle

Screened Scalar Fields in the Laboratory and the Solar System

by Hauke Fischer, Christian Käding and Mario Pitschmann

Universe 2024, 10(7), 297; https://doi.org/10.3390/universe10070297 - 15 Jul 2024

Cited by 10 | Viewed by 830

Abstract

The last few decades have provided abundant evidence for physics beyond the two standard models of particle physics and cosmology. As is now known, the by far largest part of our universe’s matter/energy content lies in the ‘dark’, and consists of dark energy [...] Read more.

The last few decades have provided abundant evidence for physics beyond the two standard models of particle physics and cosmology. As is now known, the by far largest part of our universe’s matter/energy content lies in the ‘dark’, and consists of dark energy and dark matter. Despite intensive efforts on the experimental as well as the theoretical side, the origins of both are still completely unknown. Screened scalar fields have been hypothesized as potential candidates for dark energy or dark matter. Among these, some of the most prominent models are the chameleon, symmetron, and environment-dependent dilaton. In this article, we present a summary containing the most recent experimental constraints on the parameters of these three models. For this, experimental results have been employed from the qBounce collaboration, neutron interferometry, and Lunar Laser Ranging (LLR), among others. In addition, constraints are forecast for the Casimir and Non-Newtonian force Experiment (Cannex). Combining these results with previous ones, this article collects the most up-to-date constraints on the three considered screened scalar field models. Full article

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34 pages, 17795 KiB

Open AccessArticle

Lorentzian Quantum Cosmology from Effective Spin Foams

by Bianca Dittrich and José Padua-Argüelles

Universe 2024, 10(7), 296; https://doi.org/10.3390/universe10070296 - 13 Jul 2024

Cited by 13 | Viewed by 840

Abstract

Effective spin foams provide the most computationally efficient spin foam models yet and are therefore ideally suited for applications, e.g., to quantum cosmology. Here, we provide the first effective spin foam computations of a finite time evolution step in a Lorentzian quantum de [...] Read more.

Effective spin foams provide the most computationally efficient spin foam models yet and are therefore ideally suited for applications, e.g., to quantum cosmology. Here, we provide the first effective spin foam computations of a finite time evolution step in a Lorentzian quantum de Sitter universe. We will consider a setup that computes the no-boundary wave function and a setup describing the transition between two finite scale factors. A key property of spin foams is that they implement discrete spectra for the areas. We therefore study the effects that are induced by the discrete spectra. To perform these computations, we had to identify a technique to deal with highly oscillating and slowly converging or even diverging sums. Here, we illustrate that high-order Shanks transformation works very well and is a promising tool for the evaluation of Lorentzian (gravitational) path integrals and spin foam sums. Full article

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

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11 pages, 318 KiB

Open AccessArticle

Thermodynamics of Magnetic Black Holes with Nonlinear Electrodynamics in Extended Phase Space

by Sergey Il’ich Kruglov

Universe 2024, 10(7), 295; https://doi.org/10.3390/universe10070295 - 13 Jul 2024

Viewed by 629

Abstract

We study Einstein’s gravity in AdS space coupled to nonlinear electrodynamics. Thermodynamics in extended phase space of magnetically charged black holes is investigated. We compute the metric and mass functions and their asymptotics, showing that black holes may have one or two horizons. [...] Read more.

We study Einstein’s gravity in AdS space coupled to nonlinear electrodynamics. Thermodynamics in extended phase space of magnetically charged black holes is investigated. We compute the metric and mass functions and their asymptotics, showing that black holes may have one or two horizons. The metric function is regular,

f (0) = 1

, and corrections to the Reissner–Nordström solution are in the order of

O (r^{- 3})

when the Schwarzschild mass is zero. We prove that the first law of black hole thermodynamics and the generalized Smarr relation hold. The magnetic potential and vacuum polarization conjugated to coupling are computed and depicted. We calculate the Gibbs free energy and the heat capacity showing that first-order and second-order phase transitions take place. Full article

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

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12 pages, 249 KiB

Open AccessArticle

On the Choice of Variable for Quantization of Conformal GR

by A. B. Arbuzov and A. A. Nikitenko

Universe 2024, 10(7), 294; https://doi.org/10.3390/universe10070294 - 13 Jul 2024

Viewed by 564

Abstract

The possibility of using spin connection components as basic quantization variables of a conformal version of general relativity is studied. The considered model contains gravitational degrees of freedom and a scalar dilaton field. The standard tetrad formalism is applied. Properties of spin connections [...] Read more.

The possibility of using spin connection components as basic quantization variables of a conformal version of general relativity is studied. The considered model contains gravitational degrees of freedom and a scalar dilaton field. The standard tetrad formalism is applied. Properties of spin connections in this model are analyzed. Secondary quantization of the chosen variables is performed. The gravitational part of the model action turns out to be quadratic with respect to the spin connections. So at the quantum level, the model looks trivial, i.e., without quantum self-interactions. Meanwhile the correspondence to general relativity is preserved at the classical level. Full article

(This article belongs to the Special Issue Quantum Physics including Gravity: Highlights and Novelties)

30 pages, 2160 KiB

Open AccessArticle

Isospin QCD as a Laboratory for Dense QCD

by Toru Kojo, Daiki Suenaga and Ryuji Chiba

Universe 2024, 10(7), 293; https://doi.org/10.3390/universe10070293 - 12 Jul 2024

Cited by 4 | Viewed by 842

Abstract

QCD with the isospin chemical potential

μ_{I}

is a useful laboratory to delineate the microphysics in dense QCD. To study the quark–hadron continuity, we use a quark–meson model that interpolates hadronic and quark matter physics at microscopic level. The equation of state [...] Read more.

QCD with the isospin chemical potential

μ_{I}

is a useful laboratory to delineate the microphysics in dense QCD. To study the quark–hadron continuity, we use a quark–meson model that interpolates hadronic and quark matter physics at microscopic level. The equation of state is dominated by mesons at low density but taken over by quarks at high density. We extend our previous studies with two flavors to the three-flavor case to study the impact of the strangeness, which may be brought by kaons

(K_{+}, K_{0}) = (u \bar{s}, s \bar{d})

and the U_A(1) anomaly. In the normal phase, the excitation energies of kaons are reduced by

μ_{I}

in the same way as hyperons in nuclear matter at the finite baryon chemical potential. Once pions condense, kaon excitation energies increase as

μ_{I}

does. Moreover, strange quarks become more massive through the U_A(1) coupling to the condensed pions. Hence, at zero and low temperature, the strange hadrons and quarks are highly suppressed. The previous findings in two-flavor models, sound speed peak, negative trace anomaly, gaps insensitive to

μ_{I}

, persist in our three-flavor model and remain consistent with the lattice results to

μ_{I} \sim

1 GeV. We discuss the non-perturbative power corrections and quark saturation effects as important ingredients to understand the crossover equations of state measured on the lattice. Full article

(This article belongs to the Special Issue Studies in Neutron Stars)

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34 pages, 1106 KiB

Open AccessArticle

Stochastic Tunneling in de Sitter Spacetime

by Taiga Miyachi, Jiro Soda and Junsei Tokuda

Universe 2024, 10(7), 292; https://doi.org/10.3390/universe10070292 - 11 Jul 2024

Cited by 3 | Viewed by 771

Abstract

Tunneling processes in de Sitter spacetime are studied by using the stochastic approach. We evaluate the Martin–Siggia–Rose–Janssen–de Dominicis (MSRJD) functional integral by using the saddle-point approximation to obtain the tunneling rate. The applicability conditions of this method are clarified using the Schwinger–Keldysh formalism. [...] Read more.

Tunneling processes in de Sitter spacetime are studied by using the stochastic approach. We evaluate the Martin–Siggia–Rose–Janssen–de Dominicis (MSRJD) functional integral by using the saddle-point approximation to obtain the tunneling rate. The applicability conditions of this method are clarified using the Schwinger–Keldysh formalism. In the case of a shallow potential barrier, we reproduce the Hawking–Moss (HM) tunneling rate. Remarkably, in contrast to the HM picture, the configuration derived from the MSRJD functional integral satisfies physically natural boundary conditions. We also discuss the case of a steep potential barrier and find an interesting Coleman–de Luccia (CDL) bubblelike configuration. Since the starting point of our analysis is the Schwinger–Keldysh path integral, which can be formulated in a more generic setup and incorporates quantum effects, our formalism sheds light on further studies of tunneling phenomena from a real-time perspective. Full article

(This article belongs to the Special Issue Cosmological Models of the Universe)

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28 pages, 617 KiB

Open AccessArticle

Wormhole Restrictions from Quantum Energy Inequalities

by Eleni-Alexandra Kontou

Universe 2024, 10(7), 291; https://doi.org/10.3390/universe10070291 - 6 Jul 2024

Viewed by 669

Abstract

Wormhole solutions, bridges that connect different parts of spacetime, were proposed early in the history of General Relativity. Soon after, it was shown that all wormholes violate classical energy conditions, which are non-negativity constraints on contractions of the stress–energy tensor. Since these conditions [...] Read more.

Wormhole solutions, bridges that connect different parts of spacetime, were proposed early in the history of General Relativity. Soon after, it was shown that all wormholes violate classical energy conditions, which are non-negativity constraints on contractions of the stress–energy tensor. Since these conditions are violated by quantum fields, it was believed that wormholes can be constructed in the context of semiclassical gravity. But negative energies in quantum field theory are not without restriction: quantum energy inequalities (QEIs) control renormalized negative energies averaged over a geodesic. Thus, QEIs provide restrictions on the construction of wormholes. This work is a review of the relevant literature, thus focusing on results where QEIs restrict traversable wormholes. Both ‘short’ and ‘long’ (without causality violations) wormhole solutions in the context of semiclassical gravity are examined. A new result is presented on constraints on the Maldacena, Milekhin, and Popov ‘long’ wormhole from the recently derived doubled smeared null energy condition. Full article

(This article belongs to the Special Issue The Physics of Time Travel)

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15 pages, 1242 KiB

Open AccessArticle

Molecular Formation in Low-Metallicity Hot Cores

by Yara Sobhy, Hideko Nomura, Tetsuo Yamamoto and Osama Shalabeia

Universe 2024, 10(7), 290; https://doi.org/10.3390/universe10070290 - 4 Jul 2024

Viewed by 780

Abstract

The chemical complexity in low-metallicity hot cores has been confirmed by observations. We investigate the effect of varying physical parameters, such as temperature, density and the cosmic ray ionisation rate (CRIR), on the molecular abundance evolution in low-metallicity hot cores using the UMIST [...] Read more.

The chemical complexity in low-metallicity hot cores has been confirmed by observations. We investigate the effect of varying physical parameters, such as temperature, density and the cosmic ray ionisation rate (CRIR), on the molecular abundance evolution in low-metallicity hot cores using the UMIST gas phase chemical model. CRIR had the strongest effect on molecular abundance. The resultant molecular abundances were divided into three categories with different trends in time evolution. We compared our results with the observations of hot cores in the Large Magellanic Cloud (LMC). Our model fits best with the observations at a time of around

10^{5}

years after the evaporation of ice and at the CRIR of

1.36 \times 10^{- 16}

s^{- 1}

. The resultant abundances of the oxygen-bearing complex organic molecules (COMs), such as CH₃OH, HCOOCH₃ and CH₃OCH₃, do not fit with observations in the same physical condition and may be located in a different physical environment. Our results suggest that investigating the CRIR value is crucial to predict the molecular evolution in LMC hot cores. Full article

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20 pages, 487 KiB

Open AccessArticle

On the Nature of the Radio Calibrator and Gamma-Ray Emitting NLS1 Galaxy 3C 286 and Its Multiwavelength Variability

by S. Komossa, S. Yao, D. Grupe and A. Kraus

Universe 2024, 10(7), 289; https://doi.org/10.3390/universe10070289 - 2 Jul 2024

Cited by 1 | Viewed by 1134

Abstract

The quasar 3C 286, a well-known calibrator source in radio astronomy, was found to exhibit exceptional multiwavelength properties. Its rich and complex optical emission-line spectrum revealed its narrow-line Seyfert 1 (NLS1) nature. Given its strong radio emission, this makes 3C 286 one of [...] Read more.

The quasar 3C 286, a well-known calibrator source in radio astronomy, was found to exhibit exceptional multiwavelength properties. Its rich and complex optical emission-line spectrum revealed its narrow-line Seyfert 1 (NLS1) nature. Given its strong radio emission, this makes 3C 286 one of the radio-loudest NLS1 galaxies known to date. 3C 286 is also one of very few known compact steep-spectrum (CSS) sources detected in the gamma-ray regime. Observations in the X-ray regime, rarely carried out so far, revealed evidence for variability, raising the question whether it is driven by the accretion disk or jet. 3C 286 is also well known for its damped Lyman alpha system from an intervening absorber at z = 0.692, triggering a search for the corresponding X-ray absorption along the line-of-sight. Here, we present new observations in the radio, X-ray, optical, and UV bands. The nature of the X-ray variability is addressed. Spectral evidence suggests that it is primarily driven by the accretion disk (not the jet), and the X-ray spectrum is well fit by a powerlaw plus soft excess model. The radio flux density and polarization remain constant at the Effelsberg telescope resolution, reconfirming the use of 3C 286 as radio calibrator. The amount of reddening/absorption along the line-of-sight intrinsic to 3C 286 is rigorously assessed. None is found, validating the derivation of a high Eddington ratio (

L / L_{Edd}

∼ 1) and of the very high radio-loudness index of 3C 286. Based on the first deep Chandra image of 3C 286, tentative evidence for hard X-ray emission from the SW radio lobe is reported. A large variety of models for the gamma-ray emission of 3C 286 are briefly discussed. Full article

(This article belongs to the Special Issue A Multimessenger View of Supermassive Black Holes and the Quasar Main Sequence)

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13 pages, 9643 KiB

Open AccessArticle

Mono-Higgs and Mono-Z Production in the Minimal Vector Dark Matter Model

by Gonzalo Benítez-Irarrázabal and Alfonso Zerwekh

Universe 2024, 10(7), 288; https://doi.org/10.3390/universe10070288 - 2 Jul 2024

Cited by 1 | Viewed by 675

Abstract

The minimal vector dark matter is a viable realization of the minimal dark matter paradigm. It extends the standard model by the inclusion of a vector matter field in the adjoint representation of

SU {(2)}_{L}

. The dark matter candidate [...] Read more.

The minimal vector dark matter is a viable realization of the minimal dark matter paradigm. It extends the standard model by the inclusion of a vector matter field in the adjoint representation of

SU {(2)}_{L}

. The dark matter candidate corresponds to the neutral component of the new vector field (

V^{0}

). Previous studies have shown that the model can explain the observed dark matter abundance while evading direct and indirect searches. At colliders, the attention has been put on the production of the charged companions of the dark matter candidate. In this work, we focus on the mono-Higgs and mono-Z signals at Hadron colliders. The new charged vectors (

V^{\pm}

) are invisible unless a dedicated search is performed. Consequently, we assume that the mono-Higgs and mono-Z processes correspond to the

p p \to h V^{+, 0} V^{-, 0}

and

p p \to Z V^{+, 0} V^{-, 0}

reactions, respectively. We show that, while the

p p \to h V^{+, 0} V^{-, 0}

is more important, both channels may produce significant signals at the HL-LHC and colliders running at

\sqrt{s} = 27

TeV and 100 TeV, probing almost the complete parameter space. Full article

(This article belongs to the Special Issue Search for New Physics at the LHC and Future Colliders)

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31 pages, 1771 KiB

Open AccessArticle

Energetic Particles and High-Energy Processes in Cosmological Filaments and Their Astronomical Implications

by Kinwah Wu, Ellis R. Owen, Qin Han, Yoshiyuki Inoue and Lilian Luo

Universe 2024, 10(7), 287; https://doi.org/10.3390/universe10070287 - 1 Jul 2024

Viewed by 1003

Abstract

Large-scale cosmic filaments connect galaxies, clusters, and voids. They are permeated by magnetic fields with a variety of topologies. Cosmic rays with energies up to

10^{20} eV

can be produced in astrophysical environments associated with star-formation and AGN activities. The fate of [...] Read more.

Large-scale cosmic filaments connect galaxies, clusters, and voids. They are permeated by magnetic fields with a variety of topologies. Cosmic rays with energies up to

10^{20} eV

can be produced in astrophysical environments associated with star-formation and AGN activities. The fate of these cosmic rays in filaments, which cannot be directly observed on Earth, are rarely studied. We investigate the high-energy processes associated with energetic particles (cosmic rays) in filaments, adopting an ecological approach that includes galaxies, clusters/superclusters, and voids as key cosmological structures in the filament ecosystem. We derive the phenomenology for modelling interfaces between filaments and these structures, and investigate how the transfer and fate of energetic cosmic ray protons are affected by the magnetism of the interfaces. We consider different magnetic field configurations in filaments and assess the implications for cosmic ray confinement and survival against hadronic pion-producing and photo-pair interactions. Our analysis shows that the fate of the particles depends on the location of their origin within a filament ecosystem, and that filaments act as ‘highways’, channelling cosmic rays between galaxies, galaxy clusters, and superclusters. Filaments can also operate as cosmic ‘fly paper’, capturing cosmic ray protons with energies up to

10^{18} eV

from cosmic voids. Our analysis predicts the presence of a population of ∼

10^{12}

–

10^{16} eV

cosmic ray protons in filaments and voids accumulated continually over cosmic time. These protons do not suffer significant energy losses through photo-pair or pion production, nor can they be cooled efficiently. Instead, they form a cosmic ray fossil record of the power generation history of the Universe. 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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8 pages, 420 KiB

Open AccessArticle

Galaxy Group Ellipticity Confirms a Younger Cosmos

by Yu Rong

Universe 2024, 10(7), 286; https://doi.org/10.3390/universe10070286 - 29 Jun 2024

Viewed by 642

Abstract

We present an analysis of the ellipticities of galaxy groups, derived from the spatial distribution of member galaxies, revealing a notable incongruity between the observed local galaxy groups and their counterparts in the Lambda cold dark matter cosmology. Specifically, our investigation reveals a [...] Read more.

We present an analysis of the ellipticities of galaxy groups, derived from the spatial distribution of member galaxies, revealing a notable incongruity between the observed local galaxy groups and their counterparts in the Lambda cold dark matter cosmology. Specifically, our investigation reveals a substantial disparity in the ellipticities of observed groups with masses

10^{13.0} < M_{h} < 10^{14.5} M_{⊙} h^{- 1}

exhibiting significantly higher ellipticities (at a confidence level of approximately

4 σ

) compared to their simulated counterparts. Notably, the consistent use of the same group finder for identifying galaxy groups in both observational and simulated datasets underscores the robustness of this result. This observation may imply a potential incongruence between the inferred age of the Universe from observations and the predictions of the model, which aligns with the younger Universe hypothesis suggested by the elevated fraction of observed satellite pairs with correlated line-of-sight relative velocities compared to simulations. Our findings significantly strengthen the plausibility of a younger age for our Universe. Full article

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11 pages, 5168 KiB

Open AccessReview

X17: Status and Perspectives

by Carlo Gustavino

Universe 2024, 10(7), 285; https://doi.org/10.3390/universe10070285 - 29 Jun 2024

Cited by 1 | Viewed by 772

Abstract

Recently, a group directed by A. J. Krasznahorkay observed an anomaly in the emission of electron–positron pairs in three different nuclear reactions, namely, the

^{3}

H(p,e

^{-}

e

^{+}

)

^{4}

He,

^{7}

Li(p,e

^{-}

e [...] Read more.

Recently, a group directed by A. J. Krasznahorkay observed an anomaly in the emission of electron–positron pairs in three different nuclear reactions, namely, the

^{3}

H(p,e

^{-}

e

^{+}

)

^{4}

He,

^{7}

Li(p,e

^{-}

e

^{+}

)

^{8}

Be, and

^{11}

B(p,e

^{-}

e

^{+}

)

^{12}

C processes. Kinematics indicate that this anomaly might be due to the de-excitation of

^{4}

He,

^{8}

Be, and

^{12}

C nuclei with the emission of a boson with a mass of about 17 MeV, rapidly decaying into e

^{-}

e

^{+}

pairs. The result of the experiments performed with the singletron accelerator of ATOMKI is reviewed, and the consequences of the so-called X17 boson in particle physics and in cosmology are discussed. Forthcoming experiments designed to shed light on the possible existence of the X17 boson are also reported. Full article

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

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26 pages, 388 KiB

Open AccessReview

Introduction to the Number of e-Folds in Slow-Roll Inflation

by Alessandro Di Marco, Emanuele Orazi and Gianfranco Pradisi

Universe 2024, 10(7), 284; https://doi.org/10.3390/universe10070284 - 29 Jun 2024

Cited by 1 | Viewed by 815

Abstract

In this review, a pedagogical introduction to the concepts of slow-roll inflationary universe and number of e-folds is provided. In particular, the differences between the basic notion of number of e-folds (

N_{e}

), total number of e-folds ( [...] Read more.

In this review, a pedagogical introduction to the concepts of slow-roll inflationary universe and number of e-folds is provided. In particular, the differences between the basic notion of number of e-folds (

N_{e}

), total number of e-folds (

N_{T}

) and number of e-folds before the end of inflation (N) are outlined. The proper application of the number of e-folds before the end of inflation is discussed both as a time-like variable for the scalar field evolution and as a key parameter for computing inflationary predictions. Full article

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

16 pages, 413 KiB

Open AccessArticle

Further Study of the Relationship between Transient Effects in Energetic Proton and Cosmic Ray Fluxes Induced by Coronal Mass Ejections

by Mihailo Savić, Nikola Veselinović, Darije Maričić, Filip Šterc, Radomir Banjanac, Miloš Travar and Aleksandar Dragić

Universe 2024, 10(7), 283; https://doi.org/10.3390/universe10070283 - 29 Jun 2024

Viewed by 783

Abstract

The study and better understanding of energetic transient phenomena caused by disturbances occurring on our Sun are of great importance, primarily due to the potential negative effects those events can have on Earth’s environment. Here, we present the continuation of our previous work [...] Read more.

The study and better understanding of energetic transient phenomena caused by disturbances occurring on our Sun are of great importance, primarily due to the potential negative effects those events can have on Earth’s environment. Here, we present the continuation of our previous work on understanding the connection between disturbances in the flux of energetic particles induced in the near-Earth environment by the passage of interplanetary coronal mass ejections and related Forbush decrease events. The relationship between the shape of fluence spectra of energetic protons measured by the instruments on the SOHO/ERNE probe at Lagrange point L1, Forbush decrease parameters measured by the worldwide network of neutron monitors, and coronal mass ejection parameters measured in situ is investigated. Various parameters used to characterize transient phenomena and their impact on the heliosphere, provided by the WIND spacecraft, were utilized to improve the accuracy of the calculation of the associated energetic proton fluence. The single and double power laws with exponential rollover were used to model the fluence spectra, and their effectiveness was compared. Correlation analysis between exponents used to characterize the shape of fluence spectra and Forbush decrease parameters is presented, and the results obtained by the two models are discussed. Full article

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

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13 pages, 586 KiB

Open AccessArticle

The Host Galaxy Fluxes of Active Galaxy Nuclei Are Generally Overestimated by the Flux Variation Gradient Method

by Minxuan Cai, Zhen Wan, Zhenyi Cai, Lulu Fan and Junxian Wang

Universe 2024, 10(7), 282; https://doi.org/10.3390/universe10070282 - 28 Jun 2024

Cited by 1 | Viewed by 755

Abstract

In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but [...] Read more.

In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but this assumption has been questioned by the intrinsic color variation of quasars and local Seyfert galaxies. Here, using an up-to-date thermal fluctuation model to simulate multi-wavelength AGN variability, we theoretically demonstrate that the FVG method generally overestimates the host galaxy flux; that is, it is more significant for brighter AGN/quasars. Furthermore, we observationally confirm that the FVG method indeed overestimates the host galaxy flux by comparing it to that estimated through other independent methods. We thus caution that applying the FVG method should be performed carefully in the era of time-domain astronomy. Full article

(This article belongs to the Special Issue Focus on Active Galactic Nuclei)

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9 pages, 253 KiB

Open AccessCommunication

Quantized p-Form Gauge Field in D-Dimensional de Sitter Spacetime

by Emanuel W. D. Dantas, Geová Alencar, Ilde Guedes and Milko Estrada

Universe 2024, 10(7), 281; https://doi.org/10.3390/universe10070281 - 28 Jun 2024

Viewed by 748

Abstract

In this work, we utilize the dynamic invariant method to obtain a solution for the time-dependent Schrödinger equation, aiming to explore the quantum theory of a p-form gauge field propagating in D-dimensional de Sitter spacetimes. Thus, we present a generalization, through [...] Read more.

In this work, we utilize the dynamic invariant method to obtain a solution for the time-dependent Schrödinger equation, aiming to explore the quantum theory of a p-form gauge field propagating in D-dimensional de Sitter spacetimes. Thus, we present a generalization, through the use of p-form gauge fields, of the quantization procedure for the scalar, electromagnetic, and Kalb–Ramond fields, all of which have been previously studied in the literature. We present an exact solution for the p-form gauge field when

D = 2 (p + 1)

, and we highlight the connection of the

p = 4

case with the chiral

N = 2

,

D = 10

superstring model. We could observe particle production for

D \neq 2 (p + 1)

because the solutions are time-dependent. Additionally, observers in an accelerated co-moving reference frame will also experience a thermal bath. This could have significance in the realm of extra-dimensional physics, and presents the intriguing prospect that precise observations of the Cosmic Microwave Background might confirm the presence of additional dimensions. Full article

(This article belongs to the Special Issue Quantum Physics including Gravity: Highlights and Novelties)

16 pages, 545 KiB

Open AccessArticle

The cos 2ϕ_h Asymmetry in K^± Mesons and the Λ-Hyperon-Produced SIDIS Process at Electron Ion Colliders

by Jianxi Song, Yanli Li, Shi-Chen Xue, Hui Li and Xiaoyu Wang

Universe 2024, 10(7), 280; https://doi.org/10.3390/universe10070280 - 28 Jun 2024

Viewed by 712

Abstract

We investigate the

\cos 2 ϕ_{h}

azimuthal asymmetry contributed by the coupling of the Boer–Mulders function and the Collins function in

K^{\pm}

- and

Λ

-hyperon-produced SIDIS process. The asymmetry is studied under the transverse-momentum-dependent (TMD) factorization framework at the leading [...] Read more.

We investigate the

\cos 2 ϕ_{h}

azimuthal asymmetry contributed by the coupling of the Boer–Mulders function and the Collins function in

K^{\pm}

- and

Λ

-hyperon-produced SIDIS process. The asymmetry is studied under the transverse-momentum-dependent (TMD) factorization framework at the leading order by considering the TMD evolution effects that utilize the parametrization for non-perturbative Sudakov form factors. The DGLAP evolution effects of the collinear counterpart of the Collins function of the final-state hadrons are considered by introducing the approximated evolution kernels. We utilize the available parametrization for the proton Boer–Mulders function and the Collins function of

K^{\pm}

. For the Collins function of the

Λ

hyperon, the result of the diquark spectator model is adopted due to the absence of parametrization. The numerical results of the

\cos 2 ϕ_{h}

azimuthal asymmetry are obtained in the kinematic regions of EIC and EicC. It can be shown that the asymmetry is much smaller than the Sivers asymmetry, which means that the convolution of the Boer–Mulders function and the Collins function may not be the main contributor to the

\cos 2 ϕ_{h}

asymmetry. We emphasize the importance of future measurement of the

\cos 2 ϕ_{h}

asymmetry to unravel different contributors. Full article

(This article belongs to the Special Issue The Quantum Chromodynamics: 50th Anniversary of the Discovery)

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26 pages, 2267 KiB

Open AccessArticle

Reconstruction of Fermi and eROSITA Bubbles from Magnetized Jet Eruption with Simulations

by Che-Jui Chang and Jean-Fu Kiang

Universe 2024, 10(7), 279; https://doi.org/10.3390/universe10070279 - 27 Jun 2024

Viewed by 996

Abstract

The Fermi bubbles and the eROSITA bubbles around the Milky Way Galaxy are speculated to be the aftermaths of past jet eruptions from a supermassive black hole in the galactic center. In this work, a 2.5D axisymmetric relativistic magnetohydrodynamic (RMHD) model is applied [...] Read more.

The Fermi bubbles and the eROSITA bubbles around the Milky Way Galaxy are speculated to be the aftermaths of past jet eruptions from a supermassive black hole in the galactic center. In this work, a 2.5D axisymmetric relativistic magnetohydrodynamic (RMHD) model is applied to simulate a jet eruption from our galactic center and to reconstruct the observed Fermi bubbles and eROSITA bubbles. High-energy non-thermal electrons are excited around forward shock and discontinuity transition regions in the simulated plasma distributions. The

γ

-ray and X-ray emissions from these electrons manifest patterns on the skymap that match the observed Fermi bubbles and eROSITA bubbles, respectively, in shape, size and radiation intensity. The influence of the background magnetic field, initial mass distribution in the Galaxy, and the jet parameters on the plasma distributions and hence these bubbles is analyzed. Subtle effects on the evolution of plasma distributions attributed to the adoption of a galactic disk model versus a spiral-arm model are also studied. Full article

(This article belongs to the Special Issue Black Holes and Relativistic Jets)

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9 pages, 4215 KiB

Open AccessCommunication

Prospects for AGN Studies with AXIS: AGN Fueling—Resolving Hot Gas inside Bondi Radius of SMBHs

by Ka-Wah Wong, Helen R. Russell, Jimmy A. Irwin, Nico Cappelluti and Adi Foord

Universe 2024, 10(7), 278; https://doi.org/10.3390/universe10070278 - 27 Jun 2024

Viewed by 1339

Abstract

Hot gas around a supermassive black hole (SMBH) should be captured within the gravitational “sphere of influence”, characterized by the Bondi radius. Deep Chandra observations have spatially resolved the Bondi radii of five nearby SMBHs that are believed to be accreting in hot [...] Read more.

Hot gas around a supermassive black hole (SMBH) should be captured within the gravitational “sphere of influence”, characterized by the Bondi radius. Deep Chandra observations have spatially resolved the Bondi radii of five nearby SMBHs that are believed to be accreting in hot accretion mode. Contrary to earlier hot accretion models that predicted a steep temperature increase within the Bondi radius, none of the resolved temperature profiles exhibit such an increase. The temperature inside the Bondi radius appears to be complex, indicative of a multi-temperature phase of hot gas with a cooler component at about 0.2–0.3 keV. The density profiles within the Bondi regions are shallow, suggesting the presence of strong outflows. These findings might be explained by recent realistic numerical simulations that suggest that large-scale accretion inside the Bondi radius can be chaotic, with cooler gas raining down in some directions and hotter gas outflowing in others. With an angular resolution similar to Chandra and a significantly larger collecting area, AXIS will collect enough photons to map the emerging accretion flow within and around the “sphere of influence” of a large sample of active galactic nuclei (AGNs). AXIS will reveal transitions in the inflow that ultimately fuels the AGN, as well as outflows that provide feedback to the environment. This White Paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS White Papers can be found at the AXIS website. Full article

(This article belongs to the Section Galaxies and Clusters)

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18 pages, 8503 KiB

Open AccessArticle

Effects of Two Quantum Correction Parameters on Chaotic Dynamics of Particles near Renormalized Group Improved Schwarzschild Black Holes

by Junjie Lu and Xin Wu

Universe 2024, 10(7), 277; https://doi.org/10.3390/universe10070277 - 26 Jun 2024

Viewed by 1241

Abstract

A renormalized group improved Schwarzschild black hole spacetime contains two quantum correction parameters. One parameter

γ

represents the identification of cutoff of the distance scale, and another parameter

Ω

stems from nonperturbative renormalization group theory. The two parameters are constrained by the data [...] Read more.

A renormalized group improved Schwarzschild black hole spacetime contains two quantum correction parameters. One parameter

γ

represents the identification of cutoff of the distance scale, and another parameter

Ω

stems from nonperturbative renormalization group theory. The two parameters are constrained by the data from the shadow of M87* central black hole. The dynamics of electrically charged test particles around the black hole are integrable. However, when the black hole is immersed in an external asymptotically uniform magnetic field, the dynamics are not integrable and may allow for the occurrence of chaos. Employing an explicit symplectic integrator, we survey the contributions of the two parameters to the chaotic dynamical behavior. It is found that a small change of the parameter

γ

constrained by the shadow of M87* black hole has an almost negligible effect on the dynamical transition of particles from order to chaos. However, a small decrease in the parameter

Ω

leads to an enhancement in the strength of chaos from the global phase space structure. A theoretical interpretation is given to the different contributions. The term with the parameter

Ω

dominates the term with the parameter

γ

, even if the two parameters have same values. In particular, the parameter

Ω

acts as a repulsive force, and its decrease means a weakening of the repulsive force or equivalently enhancing the attractive force from the black hole. On the other hand, there is a positive Lyapunov exponent that is universally given by the surface gravity of the black hole when

Ω \geq 0

is small and the external magnetic field vanishes. In this case, the horizon would influence chaotic behavior in the motion of charged particles around the black hole surrounded by the external magnetic field. This point can explain why a smaller value of the renormalization group parameter would much easily induce chaos than a larger value. Full article

(This article belongs to the Special Issue Testing General Relativity from the Solar System, Black Holes to Cosmology)

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20 pages, 2176 KiB

Open AccessArticle

Surveying the Onset and Evolution of Supermassive Black Holes at High-z with AXIS

by Nico Cappelluti, Adi Foord, Stefano Marchesi, Fabio Pacucci, Angelo Ricarte, Melanie Habouzit, Fabio Vito, Meredith Powell, Michael Koss and Richard Mushotzky

Universe 2024, 10(7), 276; https://doi.org/10.3390/universe10070276 - 25 Jun 2024

Cited by 4 | Viewed by 1340

Abstract

The nature and origin of supermassive black holes (SMBHs) remain an open matter of debate within the scientific community. While various theoretical scenarios have been proposed, each with specific observational signatures, the lack of sufficiently sensitive X-ray observations hinders the progress of observational [...] Read more.

The nature and origin of supermassive black holes (SMBHs) remain an open matter of debate within the scientific community. While various theoretical scenarios have been proposed, each with specific observational signatures, the lack of sufficiently sensitive X-ray observations hinders the progress of observational tests. In this white paper, we present how AXIS will contribute to solving this issue. With an angular resolution of 1.5″ on-axis and minimal off-axis degradation, we designed a deep survey capable of reaching flux limits in the [0.5–2] keV range of approximately 2 × 10⁻¹⁸ erg s⁻¹ cm⁻² over an area of 0.13 deg² in approximately 7 million seconds (7 Ms). Furthermore, we planned an intermediate depth survey covering approximately 2 deg² and reaching flux limits of about 2 × 10⁻¹⁷ erg s⁻¹ cm⁻² in order to detect a significant number of SMBHs with X-ray luminosities (L_X) of approximately 10⁴² erg s⁻¹ up to z∼10. These observations will enable AXIS to detect SMBHs with masses smaller than 10⁵ M_⊙, assuming Eddington-limited accretion and a typical bolometric correction for Type II AGN. AXIS will provide valuable information on the seeding and population synthesis models of SMBHs, allowing for more accurate constraints on their initial mass function (IMF) and accretion history from z∼0–10. To accomplish this, AXIS will leverage the unique synergy of survey telescopes such as the JWST, Roman, Euclid, Vera Rubin Telescope, and the new generation of 30 m class telescopes. These instruments will provide optical identification and redshift measurements, while AXIS will discover the smoking gun of nuclear activity, particularly in the case of highly obscured AGN or peculiar UV spectra as predicted and recently observed by the JWST in the early Universe. Full article

(This article belongs to the Section Galaxies and Clusters)

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10 pages, 1350 KiB

Open AccessArticle

Fitting the Crab Supernova with a Gamma-Ray Burst

by Remo Ruffini and Costantino Sigismondi

Universe 2024, 10(7), 275; https://doi.org/10.3390/universe10070275 - 25 Jun 2024

Viewed by 1359

Abstract

Here, we reconsider the historical data, assuming a gamma-ray burst (GRB) as its source. A Supernova correlated with the GRB explains well the fading time observed by the ancient Chinese astronomers in the daytime and the nighttime, while the GRB power law explains [...] Read more.

Here, we reconsider the historical data, assuming a gamma-ray burst (GRB) as its source. A Supernova correlated with the GRB explains well the fading time observed by the ancient Chinese astronomers in the daytime and the nighttime, while the GRB power law explains the present X-rays and GeV emission of the Crab. On the grounds of a recent understanding of the first episode of binary-driven hypernova GRB (BDHN GRB) in terms of the collapse of a ten solar masses core, we propose the possible identification of the real Supernova event at an earlier time than Chinese chronicles. This work allows a new understanding of the significance of historical astronomical observations, including a fireball due to gamma-ray air shower observation and a plague of acute radiation syndrome, documented with several thousands of victims in the Eurasian area (Egypt, Iraq, and Syria). Full article

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

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