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        <title>Frontiers in Astronomy and Space Sciences | Cosmology section | New and Recent Articles</title>
        <link>https://www.frontiersin.org/journals/astronomy-and-space-sciences/sections/cosmology</link>
        <description>RSS Feed for Cosmology section in the Frontiers in Astronomy and Space Sciences journal | New and Recent Articles</description>
        <language>en-us</language>
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        <pubDate>2026-05-14T01:15:37.740+00:00</pubDate>
        <ttl>60</ttl>
        <item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2026.1754814</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2026.1754814</link>
        <title><![CDATA[Analytic approximate charged black hole solutions in Einstein–quartic gravity]]></title>
        <pubdate>2026-03-26T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Supakchai Ponglertsakul</author><author>Seyed Naseh Sajadi</author>
        <description><![CDATA[In this work, we employ continued fraction expansions to derive analytical, approximate charged black hole solutions in Einstein–Maxwell–quartic gravity, a theory that introduces quartic curvature corrections to the Einstein–Hilbert action. To construct the full solution, we first obtain the metric function near the event horizon and at asymptotically large distances and then smoothly connect these regions using the continued fraction method. We further compute the associated thermodynamic quantities and verify the validity of the first law of black hole thermodynamics and the Smarr relation within this framework. We find that the thermodynamic analysis reveals van der Waals-type phase transitions between small and large black holes, with critical parameters that exhibit a universal ratio independent of the model parameters. Furthermore, the quasi-normal mode analysis indicates that the resulting spacetime is dynamically stable.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2026.1721816</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2026.1721816</link>
        <title><![CDATA[Studying the detectability of gravitational waves from the post-merger phase in binary neutron star signals]]></title>
        <pubdate>2026-03-02T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Gabriela Conde-Saavedra</author><author>Odylio D. Aguiar</author><author>H. P. de Oliveira</author><author>Maximiliano Ujevic</author>
        <description><![CDATA[We study the detectability of next-generation gravitational wave detectors by analyzing 10 post-merger signals in binary neutron star simulations assuming they are sources located at d=88 Mpc and d=159 Mpc. The simulation characteristics are based on the binary parameters estimated for the GW190425 event. Our results show that the most optimistic result is given by the Cosmic Explorer detector at the highest values of the merger rate (R0=1700 Gpc−3yr−1) and signal-to-noise ratio (SNRhigh=5.34±3.06), providing N=1.44±2.48 detections per year.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1710235</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1710235</link>
        <title><![CDATA[A strictly local solution to the problem of energy in general relativity]]></title>
        <pubdate>2026-02-19T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Werner M. Vieira</author><author>Nadja S. Magalhaes</author>
        <description><![CDATA[The problem of energy and its conservation is more than a century old in general relativity (GR) and is considered by many scholars to be, at least, not sufficiently solved. The problem’s core lies in the abandonment, in GR, of the non-dynamical Minkowski spacetime (within the set of inertial coordinates) in favor of dynamical Riemannian spacetimes (within the set of general coordinates), a choice that, nevertheless, has helped unravel many new phenomena, especially in astrophysics and cosmology. We turn to the subject by briefly revisiting its meaning and describing important approaches to it since the launch of GR: the pseudo-tensor approach and the non-local and global approaches. We detail the mathematical difficulties with them to highlight why they are unable to answer the problem at a fundamental level in Riemannian spacetimes, thus hindering progress in understanding not only cosmology but also quantum gravity. Based on an analysis of these issues on both mathematical and physical grounds, we propose a strictly local approach, based on what we name the principle of local balance, to provide a consistent response to the energy–momentum problem when the geometry becomes Riemannian. Finally, we demonstrate that GR only partially adheres to this principle, thereby supporting the application of the principle to search for a broader gravitational theory that reduces to GR in some appropriate limit.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1731374</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1731374</link>
        <title><![CDATA[Cosmological redshift as a manifestation of nonlinear critical relativistic quantum wave fields ]]></title>
        <pubdate>2026-02-11T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Vitaly L. Galinsky</author><author>Lawrence R. Frank</author>
        <description><![CDATA[We explore the hypothesis that both Newtonian and relativistic gravitational phenomena may emerge from critical dynamics in nonlinear relativistic wave fields, in analogy with wave–particle duality in quantum systems. Using a general nonlinear self-adjoint wave Hamiltonian, we construct a set of illustrative toy models in which increasing interaction strength drives a transition from extended, oscillatory waves to localized particle-like excitations. In this framework, gravitational and cosmological effects—including redshift—arise as collective, near-critical wave phenomena rather than as properties of a predefined spacetime geometry. The constancy of the speed of light emerges from nonlinear terms in the dispersion relation, and wave localization provides a common origin for inertial and gravitational mass without requiring a separate equivalence principle. These models also exhibit the absence of singularities (e.g., at the Schwarzschild radius or at r=0) and suggest potential connections between local gravitational behavior and large-scale structure. As a proof of concept, we show how critical-wave effects may alleviate the observed tension between Planck CMB inferences and supernova/Cepheid distance measurements without assuming FLRW metrics or ΛCDM dynamics; the same mechanism provides an alternative simple explanation for the BAO peak in the galaxy distribution function. We emphasize that these results are not proposed as a replacement for general relativity or standard cosmology, but as a conceptual demonstration that nonlinear wave dynamics can reproduce qualitative gravitational and cosmological features, motivating further investigation into emergent-gravity scenarios.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1698879</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1698879</link>
        <title><![CDATA[The importance of GR’s principle of equivalence for kinematically determined universes and consequences for ΛCDM]]></title>
        <pubdate>2026-02-09T00:00:00Z</pubdate>
        <category>Hypothesis and Theory</category>
        <author>Horst Foidl</author><author>Tanja Rindler-Daller</author>
        <description><![CDATA[The measurements of the cosmic microwave background (CMB) have determined the cosmological parameters with high accuracy, and the observation of the flatness of space has contributed to the status of the concordance Λ cold dark matter (CDM) model. However, the cosmological constant Λ, necessary to close the model to critical density, remains an open conundrum. The Einstein equations and the Friedmann–Lemaître–Robertson–Walker (FLRW) metric are the foundation of modern cosmology. While the geometric interpretation of the Einstein equations describes the action of gravity as the dynamical curvature of space by matter, the FLRW metric is built on Milne’s concept of a kinematically determined Universe. In a preceding companion article, we considered that the Friedmann equation describes the expansion history of FLRW universes in the local reference frame of freely falling comoving observers, who perceive flat, homogeneous, and isotropic space in their local inertial frame. The observed late-time accelerated expansion is then attributed to a kinematic effect akin to a dark energy component. Our approach displayed an expansion history very similar to that of ΛCDM. Now we extend our approach to nonlinear structure formation. We include the impact on the expansion history caused by the cosmic web of the late Universe, once voids dominate its volume, and find that the initially constant wde becomes time-dependent, evolving to a value of wde≃−0.9 at the present. While this impact of voids is minor, it could provide a possible explanation for the Hubble tension. We use the Cosmic Linear Anisotropy Solving System (CLASS) to calculate the expansion history and power spectra of our extension and compare our results to concordance ΛCDM and to observations. We find that our model agrees well with current data, in particular with the final data release PR4 of the Planck mission.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1675093</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1675093</link>
        <title><![CDATA[Regular Bardeen-like black holes in higher-dimensional pure Lovelock gravity with nonlinear Yang–Mills fields]]></title>
        <pubdate>2025-10-15T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>S. Habib Mazharimousavi</author>
        <description><![CDATA[IntroductionWe construct spherically symmetric, static, and regular Bardeen-like black hole solutions in the framework of higher-dimensional pure Lovelock gravity coupled to nonlinear Yang–Mills (YM) fields. The aim is to generalize the notion of regular black holes to higher-curvature gravity theories while preserving regularity and asymptotic flatness.MethodsThe gauge fields are modeled using a higher-dimensional Wu–Yang ansatz, and the nonlinear YM Lagrangian is designed to reproduce Bardeen-type configurations known from Einstein gravity. The field equations are solved analytically to obtain exact metric functions, and curvature invariants are computed to verify the regularity of the spacetime.ResultsThe resulting solutions are asymptotically flat and regular at the origin, with all curvature invariants remaining finite throughout the spacetime. In dimensions N=2p+1, the configurations describe particle-like solutions without horizons. For N>2p+1, depending on the model parameters, the solutions can represent either regular black holes or particle-like spacetimes. Analytic conditions determining the existence and number of horizons are derived, allowing for a full classification of the spacetime structure.DiscussionA detailed thermodynamic analysis is performed by computing the Hawking temperature and heat capacity. The phase structure reveals regions of thermal stability and the occurrence of first- and second-order phase transitions. These findings extend the concept of regular black holes to pure Lovelock gravity and emphasize the rich interplay between nonlinearity, dimensionality, and gauge dynamics.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1647284</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1647284</link>
        <title><![CDATA[Gravitational interactions with information dynamics]]></title>
        <pubdate>2025-09-22T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Mahgoub A. Salih</author>
        <description><![CDATA[IntroductionUnifying gravity with quantum mechanics remains a cornerstone challenge in physics, with information theory providing a transformative perspective through concepts like the holographic principle and entropic gravity.MethodsWe derive an observer-independent information density field from coarse-grained Shannon entropy of classical matter configurations at nuclear scales, establish thermodynamically motivated coupling constants using hadronic physics, prove gauge invariance including novel information symmetries, and enhance experimental designs with detailed error budgets and theory differentiation.ResultsThe framework predicts modified gravitational lensing corrections (δ∼10−8) and quantum phase shifts (Δϕ∼10−12 rad), verifiable within 1–5 years using precision astrometry and matter-wave interferometry, supported by comprehensive derivations, Python verification code, and professional diagrams.DiscussionThis work positions information-theoretic gravity as a rigorous, testable paradigm that bridges classical relativity and quantum information, with potential extensions to broader unification while maintaining focus on gravitational interactions.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1627777</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1627777</link>
        <title><![CDATA[The importance of GR’s principle of equivalence for kinematically determined Friedmann–Lemaître–Robertson–Walker universes]]></title>
        <pubdate>2025-09-04T00:00:00Z</pubdate>
        <category>Hypothesis and Theory</category>
        <author>Horst Foidl</author><author>Tanja Rindler-Daller</author>
        <description><![CDATA[The Einstein equations and the Friedmann–Lemaître–Robertson–Walker (FLRW) metric are the foundation of modern cosmology. Whereas the geometric interpretation of the Einstein equations describes the action of gravity as the curvature of space by matter, the FLRW metric is built on Milne’s concept of a kinematically determined universe. Applying the FLRW metric to the Einstein equations yields the Friedmann equation which describes the expansion history of the universe in the reference frame of observers co-moving with the expansion, who, as a consequence of the equivalence principle, are free-falling, co-moving observers and perceive flat space in their local inertial frame. We use this fact to propose an extension to ΛCDM, incorporating the initial conditions of the background universe, comprising the initial energy densities and the initial post-big bang expansion rate. The observed late-time accelerated expansion is then attributed to a kinematic effect akin to a dark energy (DE) component. Choosing the same Ωm,0≃0.3 as ΛCDM, its equation of state parameter is wde≃−0.8. The expansion history of this model displays the typical s-shape in the evolution of the scale factor, which is known from the ΛCDM concordance model.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1538434</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1538434</link>
        <title><![CDATA[A review of basic results on the Bose–Einstein condensate dark matter model]]></title>
        <pubdate>2025-08-20T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Pierre-Henri Chavanis</author>
        <description><![CDATA[We review basic results on the Bose–Einstein condensate dark matter (BECDM) model. Self-gravitating BECs experience a collisionless process of gravitational cooling and violent relaxation, leading to BECDM halos with a “core-envelope” structure. The quantum core (soliton), which is the ground state of the Gross–Pitaevskii–Poisson (GPP) equations, may solve the core–cusp problem of the cold dark matter (CDM) model. The approximately isothermal envelope, resulting from the quantum interferences of the excited states, is similar to the Navarro–Frenk–White (NFW) profile of CDM halos and accounts for the flat rotation curves of the galaxies. We derive the core mass–radius relation, the halo mass–radius relation, and the core mass–halo mass relation of BECDM halos. We show that the core mass increases with the halo mass and we discuss the possibility that it collapses above a maximum mass arising from general relativity or from the attractive self-interaction of the bosons. We discuss the secular evolution of BECDM halos induced by the formation of granules (or quasiparticles) in the envelope, and we mention the analogy with the evolution of globular clusters. We also discuss the basic elements of BECDM cosmology. Throughout this review, we emphasize the importance of the maximum mass of dilute axion stars with an attractive self-interaction [P.H. Chavanis, Phys. Rev. D 84, 043531 (2011)] and its consequences.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1613180</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1613180</link>
        <title><![CDATA[Editorial: Neutron stars and quark stars inside out]]></title>
        <pubdate>2025-05-13T00:00:00Z</pubdate>
        <category>Editorial</category>
        <author>Chen Zhang</author><author>Yongfeng Huang</author><author>Renxin Xu</author><author>Hajime Togashi</author><author>Chengjun Xia</author><author>Alexander Rodin</author>
        <description></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1589644</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1589644</link>
        <title><![CDATA[Editorial: Scalar fields and the dark universe]]></title>
        <pubdate>2025-03-27T00:00:00Z</pubdate>
        <category>Editorial</category>
        <author>Tonatiuh Matos</author><author>Luis Urena-Lopez</author>
        <description></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2025.1563337</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2025.1563337</link>
        <title><![CDATA[Editorial: Experimental predictions in general relativity: what now?]]></title>
        <pubdate>2025-02-28T00:00:00Z</pubdate>
        <category>Editorial</category>
        <author>Fabiano Feleppa</author><author>Elmo Benedetto</author><author>Gerardo Iovane</author><author>Fabrizio Tamburini</author><author>Ignazio Licata</author>
        <description></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2024.1386305</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2024.1386305</link>
        <title><![CDATA[Cosmic ray contributions from rapidly rotating stellar mass black holes: cosmic Ray GeV to EeV proton and anti-proton sources]]></title>
        <pubdate>2024-12-20T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>M. Allen</author><author>P. L. Biermann</author><author>A. Chieffi</author><author>R. Chini</author><author>D. Frekers</author><author>L. Gergely</author><author> Gopal-Krishna</author><author>B. Harms</author><author>I. Jaroschewski</author><author>P. S. Joshi</author><author>P. P. Kronberg</author><author>E. Kun</author><author>A. Meli</author><author>E.-S. Seo</author><author>T. Stanev</author>
        <description><![CDATA[In Radio Super Novae (RSNe) a magnetic field of (B × r) = 1016.0±0.12 Gauss × cm is observed; these are the same numbers for Blue Super Giant (BSG) star explosions as for Red Super Giant (RSG) star explosions, despite their very different wind properties. The EHT data for M87 as well for low power radio galaxies all show consistency with just this value of the quantity (B × r), key for angular momentum and energy transport, and can be derived from the radio jet data. We interpret this as a property of the near surroundings of a black hole (BH) at near maximal rotation, independent of BH mass. In the commonly used green onion model, in which a 2 π flow changes over to a jet flow we interpret this as a wind emanating from the BH/accretion disk system and its surroundings. Near the BH collisions in the wind can produce a large fraction of anti-protons. In this scenario the cosmic Ray (CR) population from the wind/jet is proposed to be visible as EeV protons and anti-protons in the CR data to EeV energy, with a E−7/3 spectrum. This can be connected to a concept of inner and outer Penrose zones in the ergo-region. The observed numbers for the magnetic field imply the Planck time as the governing time scale: A BH rotating near maximum can accept a proton per log bin of energy in an extended spectrum with the associated pions every Planck time.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2024.1401785</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2024.1401785</link>
        <title><![CDATA[NASA’s astrophysics cross-observatory science support (ACROSS) initiative: enabling time-domain and multimessenger astrophysics]]></title>
        <pubdate>2024-11-15T00:00:00Z</pubdate>
        <category>Methods</category>
        <author>T. B. Humensky</author><author>C. J. Roberts</author><author>T. Barclay</author><author>R. Caputo</author><author>S. B. Cenko</author><author>F. Civano</author><author>J. Derleth</author><author>C. Hedges</author><author>M. C. Hui</author><author>J. A. Kennea</author><author>D. Kocevski</author><author>J. Racusin</author><author>B. Rani</author><author>R. M. Sambruna</author><author>J. Slutsky</author>
        <description><![CDATA[The Astro2020 Decadal Survey recommended an investment in Time-Domain and Multimessenger Astrophysics (TDAMM) as the top-priority sustaining activity in space for the coming decade. One aspect of NASA’s response to this recommendation is a pilot project, the Astrophysics Cross-Observatory Science Support (ACROSS) initiative, designed to provide support to both missions and observers as they pursue TDAMM science. Here, we present our observations of needs in the community and initial plans for ACROSS activities, including services to facilitate and improve cross-mission follow-up planning and execution; a multimessenger web portal with links to existing mission resources, community tools, and information targeted for TDAMM general observers; development of “Smart target-of-opportunity submission page” proof-of-concepts; and ongoing development of a potential TDAMM general observing competitive grant solicitation. As the ACROSS pilot phase begins, we invite discussion of our plans with both missions and observers to better understand their needs and concerns.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2024.1477677</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2024.1477677</link>
        <title><![CDATA[Search for thermonuclear burst oscillations in the Swift/BAT data set]]></title>
        <pubdate>2024-10-08T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Qing-Xin Li</author><author>Zhaosheng Li</author><author>Yuan-Yue Pan</author><author>Maurizio Falanga</author>
        <description><![CDATA[This study comprehensively analyzes type I X-ray bursts observed by Swift/BAT from 2005 to April 2024 to search for X-ray burst oscillations (XBOs) in neutron star low-mass X-ray binaries. XBOs, periodic signals detected within type I X-ray bursts, typically range from 11 to 620 Hz and are often observed in the soft X-ray data of these bursts. Using the high-sensitivity and precise timing capabilities of the Swift/BAT, we found 50 type I X-ray bursts from 37 neutron star low-mass X-ray binaries. We conducted a detailed timing analysis of these bursts. For sources with known burst oscillation frequencies, our findings largely corroborate previous studies. However, many sources displayed low confidence levels in the oscillation signals, with Z12 values between 10 and 20. For sources without known oscillation/spin frequencies, we utilized FFT analysis to search for signals across a broad frequency range. This approach revealed potential oscillation signals, with several bursts showing significance levels exceeding 3σ, including those from MAXI J1421–613, XTE J1701–407, XMM J174457–2850.3, Swift J1734.5–3027, IGR J17473–2721, Swift J174805.3–244637, Swift J181723.1–164300, and X 1832–330.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2024.1401891</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2024.1401891</link>
        <title><![CDATA[Multi-messenger emission characteristics of blazars]]></title>
        <pubdate>2024-09-05T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Ronald Gamble</author><author>Jordan Forman</author><author>Amethyst Barnes</author><author>Gokul Srinivasaragavan</author><author>Isiah Holt</author><author>Marvin Jones</author>
        <description><![CDATA[Multi-messenger observations and theories of astrophysical objects are rapidly becoming a critical research area in the astrophysics scientific community. In particular, point-like objects such as BL Lacertae (BL Lac) objects, flat-spectrum radio quasars (FSRQs), and blazar candidates of uncertain type (BCUs) are of distinct interest to researchers studying the synchrotron, Compton, neutrino, and cosmic ray emissions sourced from compact objects. Notably, there is also much interest in the correlation between multi-frequency observations of blazars and neutrino surveys on source demographics. In this review, we look at such multi-frequency and multi-physics correlations of the radio, X-ray, and γ-ray fluxes of different classes of blazars from a collection of survey catalogs. This multi-physics survey of blazars shows that there are characteristic cross-correlations in the spectra of blazars when considering their multi-frequency and multi-messenger emission. In addition, a review of cosmic ray and neutrino emissions from blazars and their characteristics is presented.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2024.1409463</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2024.1409463</link>
        <title><![CDATA[Recent progresses in strange quark stars]]></title>
        <pubdate>2024-08-21T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Xiao-Li Zhang</author><author>Yong-Feng Huang</author><author>Ze-Cheng Zou</author>
        <description><![CDATA[According to the hypothesis that strange quark matter may be the true ground state of matter at extremely high densities, strange quark stars should be stable and could exist in the Universe. It is possible that pulsars may actually be strange stars, but not neutron stars. Here we present a short review on recent progresses in the field of strange quark stars. First, three popular phenomenological models widely used to describe strange quark matter are introduced, with special attention being paid on the corresponding equation of state in each model. Combining the equation of state with the Tolman-Oppenheimer-Volkov equations, the inner structure and mass-radius relation can be obtained for the whole sequence of strange stars. Tidal deformability and oscillations (both radial and non-radial oscillations), which are sensitive to the composition and the equations of state, are then described. Hybrid stars as a special kind of quark stars are discussed. Several other interesting aspects of strange stars are also included. For example, strong gravitational wave emissions may be generated by strange stars through various mechanisms, which may help identify strange stars via observations. Especially, close-in strange quark planets with respect to their hosts may provide a unique test for the existence of strange quark objects. Fierce electromagnetic bursts could also be generated by strange stars. The energy may come from the phase transition of neutron stars to strange stars, or from the merger of binary strange stars. The collapse of the strange star crust can also release a huge amount of energy. It is shown that strange quark stars may be involved in short gamma-ray bursts and fast radio bursts.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2024.1426406</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2024.1426406</link>
        <title><![CDATA[Scalar field solutions and energy bounds for modeling spatial oscillations in Schwarzschild black holes based on the Regge–Wheeler equation]]></title>
        <pubdate>2024-08-20T00:00:00Z</pubdate>
        <category>Brief Research Report</category>
        <author>José Luis Díaz Palencia</author>
        <description><![CDATA[This text discusses the behavior of solutions and the energy stability within Schwarzschild spacetimes, with a particular emphasis on the behavior of massless scalar fields under the influence of a non-rotating and spherically symmetric black hole. The stability of solutions in the proximity of the event horizon of black holes in general relativity remains an open question, especially given the difficulties introduced by minor perturbations that may resemble Kerr solutions. To address this, this work explores a simplified model, including massless scalar fields, to better understand perturbation behaviors around black holes under the Schwarzschild approach. We depart from Richard Price’s work in connection with how scalar, electromagnetic, and gravitational fields behave. The tortoise coordinate transformation is considered to set the stage for numerical solutions to the wave equations. Afterward, we explore energy estimates, which are used to gauge stability and wave behavior over time. Our analysis reveals that the time evolution of the energy does not exceed twice its initial value. Further and under the assumption of initial conditions in L2−spaces, we obtain an exponential decreasing behavior in the energy time evolution. A question to continue exploring is how perturbations in L2 in the initial conditions that introduce Kerr solutions as a second-order effect in the linearized equations perturb this obtained exponential decay.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2024.1453806</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2024.1453806</link>
        <title><![CDATA[Constraining the minimally extended varying speed of light model using time dilations]]></title>
        <pubdate>2024-08-02T00:00:00Z</pubdate>
        <category>Mini Review</category>
        <author>Seokcheon Lee</author>
        <description><![CDATA[The Robertson–Walker (RW) metric, derived from the cosmological principle and Weyl’s postulate, characterizes the ΛCDM cosmological model. Traditionally, in this framework, the assumption of a constant speed of light leads to specific cosmological time dilation (TD). However, because the Robertson–Walker metric lacks a way to define time dilation, the speed of light, like wavelength and temperature, may vary with cosmic time. The minimally extended varying speed of light (meVSL) model fits standard cosmological observations while considering the evolution of physical constants. One model-independent test for the meVSL model is cosmological time dilation. However, current data cannot distinguish between the meVSL model and the standard model.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fspas.2024.1429235</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fspas.2024.1429235</link>
        <title><![CDATA[A machian model as potential alternative to dark matter halo thesis in galactic rotational velocity prediction]]></title>
        <pubdate>2024-08-01T00:00:00Z</pubdate>
        <category>Hypothesis and Theory</category>
        <author>Stephan Walrand</author>
        <description><![CDATA[A novel axially symmetric metric is proposed to solve the Einstein field equations. This provides an analytical solution within the matter in the equatorial plane for any galaxy density profile. The solution predicts the observed increase in rotational velocity up to the edge of the galaxy’s bulge. However, beyond the bulge, the rotational velocity remains constant, which contradicts the observed peak curves. The existence of the Universe is then considered by approximating the gravitational fields within the galaxy as the sum of those generated by the galaxy and the Universe. The resulting solution explicitly includes a Universe frame-dragging term, aligning with the sixth version of Mach’s principle proposed by Bondi and Samuel: “inertial mass is affected by the global distribution of matter”. Neglecting the presence of the Universe, stars only have a relative rotation to the bulge, and their rotational velocities monotonically increase with the radial distance r to balance the increasing mass contained in distances < r. At larger distances, the bulge’s attraction and its frame-dragging effect decrease, resulting in a constant rotational velocity. When the Universe is considered, stars also have a relative rotation to the non-rotating Universe and experience an additional centrifugal force at any distance from the bulge. This component induces a decrease in rotational velocity as the gravitational influence of the bulge diminishes with r. This model predicts the observed rotational velocity curves for the galaxies M31, M101, and M81 without requiring any dark matter halo or adjustable parameters. This success substantiates Mach’s idea as an alternative to the dark matter halo theory.]]></description>
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