Universe

28 pages, 621 KiB

Open AccessArticle

Wormhole Restrictions from Quantum Energy Inequalities

by Eleni-Alexandra Kontou

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

Viewed by 126

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)

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 237

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, 484 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 (registering DOI) - 2 Jul 2024

Viewed by 254

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

Viewed by 231

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 296

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, 407 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 199

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

11 pages, 5163 KiB

Open AccessReview

X17: Status and Perspectives

by Carlo Gustavino

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

Viewed by 209

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

^{+}

)

^{8}

Be, and

^{11}

B(p,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)

26 pages, 403 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

Viewed by 180

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 difference between the basic notion of e-folds (

N_{e}

) the 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 difference between the basic notion of e-folds (

N_{e}

) the total number of e-folds (

N_{T}

) and the number of e-folds before the end of inflation (N) is 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, 406 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 235

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 System)

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

Viewed by 305

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 268

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 **aoyu Wang

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

Viewed by 260

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, 2258 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 328

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)

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 481

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, 8494 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 **n Wu

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

Viewed by 692

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 ≥ 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)

20 pages, 2185 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

Viewed by 654

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 deg

^{2}

in approximately 7 million seconds (7 Ms). Furthermore, we planned an intermediate depth survey covering approximately 2 deg

^{2}

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 10

^{42}

erg s

^{- 1}

up to z ∼ 10. These observations will enable AXIS to detect SMBHs with masses smaller than 10

^{5}

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)

10 pages, 580 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 642

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 Stellar Astronomy)

15 pages, 844 KiB

Open AccessArticle

Serendipitous Discovery of a 431 ms Pulsar in the Background of Westerlund 1

by Viviana Piga, Marta Burgay, Andrea Possenti, Alessandro Ridolfi, Maura Pilia, Nanda Rea, Rosalba Perna, Monica Colpi and Gianluca Israel

Universe 2024, 10(7), 274; https://doi.org/10.3390/universe10070274 - 25 Jun 2024

Viewed by 650

Abstract

We report the discovery of PSR J1646−4545, a 431 ms isolated pulsar, in the direction of the young massive cluster Westerlund 1. The pulsar was found in data taken between the years 2005 and 2010 with the “Murriyang” Parkes radio telescope in Australia. [...] Read more.

We report the discovery of PSR J1646−4545, a 431 ms isolated pulsar, in the direction of the young massive cluster Westerlund 1. The pulsar was found in data taken between the years 2005 and 2010 with the “Murriyang” Parkes radio telescope in Australia. Thanks to the numerous detections of the pulsar, we were able to derive a phase-connected timing solution spanning the whole data set. This allowed us to precisely locate the pulsar at the border of the cluster and to measure its spin-down rate. The latter implies a characteristic age of ∼25 Myr, about twice as large as the estimated age of Westerlund 1. The age of PSR J1646−4545, together with its dispersion measure of ∼1029 pc cm

^{- 3}

, more than twice the value predicted by the two main galactic electron density models for Westerlund 1, makes the association of the pulsar with the cluster highly unlikely. We also report on ramifications from the presence of a magnetar in Westerlund 1 and the apparent lack of ordinary radio pulsars. Full article

(This article belongs to the Special Issue New Insights in Fast Radio Bursts)

27 pages, 2374 KiB

Open AccessArticle

The Evolution of Galaxies and Clusters at High Spatial Resolution with Advanced X-ray Imaging Satellite (AXIS)

by Helen R. Russell, Laura A. Lopez, Steven W. Allen, George Chartas, Prakriti Pal Choudhury, Renato A. Dupke, Andrew C. Fabian, Anthony M. Flores, Kristen Garofali, Edmund Hodges-Kluck, Michael J. Koss, Lauranne Lanz, Bret D. Lehmer, Jiang-Tao Li, W. Peter Maksym, Adam B. Mantz, Michael McDonald, Eric D. Miller, Richard F. Mushotzky, Yu Qiu, Christopher S. Reynolds, Francesco Tombesi, Paolo Tozzi, Anna Trindade-Falcão, Stephen A. Walker, Ka-Wah Wong, Mihoko Yukita and Congyao Zhang Show full author list Hide full author list

Universe 2024, 10(7), 273; https://doi.org/10.3390/universe10070273 - 25 Jun 2024

Viewed by 354

Abstract

Stellar and black hole feedback heat and disperse surrounding cold gas clouds, launching gas flows off circumnuclear and galactic disks, producing a dynamic interstellar medium. On large scales bordering the cosmic web, feedback drives enriched gas out of galaxies and groups, seeding the [...] Read more.

Stellar and black hole feedback heat and disperse surrounding cold gas clouds, launching gas flows off circumnuclear and galactic disks, producing a dynamic interstellar medium. On large scales bordering the cosmic web, feedback drives enriched gas out of galaxies and groups, seeding the intergalactic medium with heavy elements. In this way, feedback shapes galaxy evolution by shutting down star formation and ultimately curtailing the growth of structure after the peak at redshift 2–3. To understand the complex interplay between gravity and feedback, we must resolve both the key physics within galaxies and map the impact of these processes over large scales, out into the cosmic web. The Advanced X-ray Imaging Satellite (AXIS) is a proposed X-ray probe mission for the 2030s with arcsecond spatial resolution, large effective area, and low background. AXIS will untangle the interactions of winds, radiation, jets, and supernovae with the surrounding interstellar medium across the wide range of mass scales and large volumes driving galaxy evolution and trace the establishment of feedback back to the main event at cosmic noon. This white paper is part of a series commissioned for the AXIS Probe mission concept; additional AXIS white papers can be found at the AXIS website. Full article

(This article belongs to the Section Galaxies and Clusters)

17 pages, 570 KiB

Open AccessArticle

FLRW Transit Cosmological Model in f(R,T) Gravity

by Vijay Singh, Siwaphiwe Jokweni and Aroonkumar Beesham

Universe 2024, 10(7), 272; https://doi.org/10.3390/universe10070272 - 24 Jun 2024

Viewed by 354

Abstract

A Friedmann–Lemaitre–Robertson–Walker space–time model with all curvatures

k = 0, \pm 1

is explored in

f (R, T)

gravity, where R is the Ricci scalar, and T is the trace of the energy–momentum tensor. The solutions are obtained via [...] Read more.

A Friedmann–Lemaitre–Robertson–Walker space–time model with all curvatures

k = 0, \pm 1

is explored in

f (R, T)

gravity, where R is the Ricci scalar, and T is the trace of the energy–momentum tensor. The solutions are obtained via the parametrization of the scale factor that leads to a model transiting from a decelerated universe to an accelerating one. The physical features of the model are discussed and analyzed in detail. The study shows that

f (R, T)

gravity can be a good alternative to the hypothetical candidates of dark energy to describe the present accelerating expansion of the universe. Full article

(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)

6 pages, 220 KiB

Open AccessCommunication

The de Sitter Swampland Conjectures in the Context of Chaplygin-Inspired Inflation

by Orfeu Bertolami, Robertus Potting and Paulo M. Sá

Universe 2024, 10(7), 271; https://doi.org/10.3390/universe10070271 - 23 Jun 2024

Viewed by 290

Abstract

In this work, we discuss the de Sitter swampland conjectures in the context of the generalized Chaplygin-inspired inflationary model. We demonstrate that these conjectures can be satisfied, but only in the region of the parameter space far away from the General Relativity limit. [...] Read more.

In this work, we discuss the de Sitter swampland conjectures in the context of the generalized Chaplygin-inspired inflationary model. We demonstrate that these conjectures can be satisfied, but only in the region of the parameter space far away from the General Relativity limit. The cosmic microwave background data had already been found to restrict the allowed inflationary potentials of this model. Our results impose a further limitation on the possible potentials. Full article

(This article belongs to the Special Issue Origins and Natures of Inflation, Dark Matter and Dark Energy, 2nd Edition)

25 pages, 518 KiB

Open AccessArticle

Non-Minimally Coupled Electromagnetic Fields and Observable Implications for Primordial Black Holes

by Susmita Jana and S. Shankaranarayanan

Universe 2024, 10(7), 270; https://doi.org/10.3390/universe10070270 - 22 Jun 2024

Viewed by 280

Abstract

General relativity (GR) postulates have been verified with high precision, yet our understanding of how gravity interacts with matter fields remains incomplete. Various modifications to GR have been proposed in both classical and quantum realms to address these interactions within the strong gravity [...] Read more.

General relativity (GR) postulates have been verified with high precision, yet our understanding of how gravity interacts with matter fields remains incomplete. Various modifications to GR have been proposed in both classical and quantum realms to address these interactions within the strong gravity regime. One such approach is non-minimal coupling (NMC), where the space-time curvature (scalar and tensor) interacts with matter fields, resulting in matter fields not following the geodesics. To probe the astrophysical implications of NMC, in this work, we investigate non-minimally coupled electromagnetic (EM) fields in the presence of black holes. Specifically, we show that primordial black holes (PBHs) provide a possible tool to constrain the NMC parameter. PBHs represent an intriguing cosmological black hole class that does not conform to the no-hair theorem. We model the PBH as a Sultana–Dyer black hole and compare it with Schwarzschild. We examine observables such as the radius of the photon sphere, critical impact parameter, and total deflection angles for non-minimally coupled photons for Schwarzschild and Sultana–Dyer black holes. Both the black hole space-times lead to similar constraints on the NMC parameter. For a PBH of mass

M = 10^{- 5} M_{⊙}

, the photon sphere will not be formed for one mode. Hence, the photons forming the photon sphere will be highly polarized, potentially leading to observable implications. Full article

(This article belongs to the Collection Open Questions in Black Hole Physics)

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Universe, Volume 10, Issue 7 (July 2024) – 22 articles

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