Astrophysics and Space Science最新文献

{"title":"Hubble IR cutoff in Bianchi (VI_{0}) universe with (f(R, L_{m})) gravity: constraints from OHD and Pantheon+SHOES observational data","authors":"G. U. Khapekar, Mohammad Muzammil Mohammad Mukhtar, Syed Mudassir Syed Iqbal","doi":"10.1007/s10509-026-04556-6","DOIUrl":"10.1007/s10509-026-04556-6","url":null,"abstract":"<div><p>In this paper, we have discussed a spatially homogeneous and anisotropic Bianchi-type <span>(VI_{0})</span> space-time in the presence of holographic dark energy with the Hubble horizon as the infrared cut-off within the frame of the non-linear <span>(f(R, L_{m}))</span> gravity model <span>(f(R, L_{m})=beta R+ L_{m}^{alpha })</span>, where <span>(alpha )</span> and <span>(beta )</span> are the free parameters. Then we have obtained the modified Friedmann equations and solved them by presuming an expansion scalar <span>(theta (t))</span> is proportional to the shear scalar <span>(sigma (t))</span>, which yields the analytical relation between metric potentials as <span>(A=B^{n})</span>, where <span>(n)</span> is constant. Also, we adopted the hyperbolic scale factor <span>(a(t)=sqrt[eta ]{sinh {t}})</span>, where <span>(eta >0)</span> is constant. Then we estimate the best fit values of model parameters by using a Chi-square test coupled with Markov Chain Monte Carlo (MCMC) simulations, based on Observational Hubble Data (OHD) with 31 points and Pantheon+SHOES data with 1701 points. This approach results in the best fit ranges for model parameters as: <span>(eta = 1.3_{-0.09}^{+0.08})</span>, <span>(H_{0}=65.97_{-2.42}^{+2.48})</span> km/s/Mpc for OHD and <span>(eta = 1.2_{-0.04}^{+0.04})</span>, <span>(H_{0}=72.77_{-0.26}^{+0.24})</span> km/s/Mpc for the Pantheon+SHOES dataset. Our analysis yields a value for <span>(H_{0})</span> that closely aligns with the Planck Collaboration’s 2018 estimate of <span>(H_{0} = 67.4 pm 0.5)</span> km/s/Mpc. With these imposed constraints, we derived the deceleration parameter <span>(q)</span>, indicating a shift from a previously decelerating phase to the current phase of accelerating expansion, with <span>(q_{0} = -0.35)</span> (OHD) as well as <span>(q_{0} = -0.4)</span> (Pantheon+SHOES). Then we analyzed the nature of the <span>(Om(z))</span> diagnostic parameter, which shows that our universe shows quintessence-type behavior. Additionally, we examined the behavior of energy density, pressure, and the equation of state (EoS) parameter using the holographic dark energy (HDE) model, incorporating Hubble’s horizon as the infrared (IR) cutoff. The equation of state parameter <span>(omega )</span> in our model demonstrates that the universe is currently in a quintessence phase, where dark energy behaves as a dynamical component rather than a cosmological constant <span>(omega =-1)</span>. Subsequently, the stability of our model was evaluated by analyzing the sound speed squared, denoted as <span>(v_{s}^{2})</span>. Finally, we examined the properties of different energy conditions in the context of stability analysis. The DEC and WEC support the model’s credibility due to their positive nature, whereas the violation of SEC suggests the universe is undergoing accelerated expansion. Our analysis reveals that the HDE cosmological model aligns well with recent observational research and effectively accoun","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 3","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147441350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stability and bifurcations of symmetrical 3D-periodic orbits in the Sitnikov five-body problem","authors":"L. P. Pandey,&nbsp;Binay Kumar Sharma,&nbsp;Rahul Tomar","doi":"10.1007/s10509-026-04557-5","DOIUrl":"10.1007/s10509-026-04557-5","url":null,"abstract":"<div><p>We have studied the variations in stability, bifurcation, critical velocity, Lagrange points, and critical periodic orbits in the context of the transition from the Sitnikov four-body system (as analyzed by Soulis et al. (Celest. Mech. Dyn. Astron. 100:251–266, 2008)) to the Sitnikov five-body system. The incorporation of one primary body results in a reduction in critical velocity and an increase in the number of stability intervals. We applied Floquet’s theory to study the stability/instability of the motion of negligible mass. For this, we assume <span>(z_{in})</span> as family parameter and vary it in the interval <span>([0, 10])</span>. Upon slightly perturbing the negligible mass from the z-axis, we obtained 13 Lagrange points. We have determined three-dimensional families of periodic orbits which bifurcate from the critical points/bifurcation points. We observed that the bifurcation points lie within the interval <span>([1.0709360, 2.7944120])</span>. We have discussed stability/instability of periodic orbits bifurcating from the critical points.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 3","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147441509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Accretion geometry of black hole X-ray binaries: insights from X-ray observations","authors":"Honghui Liu","doi":"10.1007/s10509-026-04562-8","DOIUrl":"10.1007/s10509-026-04562-8","url":null,"abstract":"<div><p>The accretion-ejection activities of black holes play a vital role in shaping the Universe. Bright and recurrent black hole X-ray binaries are ideal objects for studying accretion physics across a wide range of accretion rates, providing insights into the understanding of their supermassive counterparts. This short review summarizes X-ray techniques capable of measuring accretion geometry, our current understanding, and open questions. In particular, X-ray spectroscopic studies indicate that the accretion disk can extend close to the innermost stable circular orbit in the bright hard state. Some hints of disk-corona-jet connections are also discussed.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 3","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147441072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaluating cosmic expansion (f(mathcal{T})) vs (f(R,T)) gravity theories","authors":"Rahul Sharma,&nbsp;R. K. Mishra","doi":"10.1007/s10509-026-04560-w","DOIUrl":"10.1007/s10509-026-04560-w","url":null,"abstract":"<div><p>This study presents a comparative analysis of two modified theories of gravity, <span>(f(R,T))</span> and <span>(f(mathcal{T}))</span>, within the framework of a locally rotationally symmetric Bianchi type-I spacetime. The primary objective is to explore the role of curvature-matter coupling and torsional dynamics in explaining the universe’s late-time acceleration without invoking a cosmological constant. To solve the highly nonlinear field equations, a hyperbolic sine scale factor and a shear-expansion proportionality condition are employed. The resulting models are constrained using observational Hubble parameter data via a <span>(chi ^{2})</span> minimization technique. Key cosmological quantities, including energy density, pressure, and the equation of state (EoS) parameter, are analyzed alongside geometrical diagnostics such as the <span>(operatorname{Om}(z))</span> and statefinder parameters. Statistical tools like the Akaike and Bayesian information criteria (AIC/BIC) are used to assess model performance relative to <span>(Lambda)</span>CDM. Results show that both models capture the transition from decelerated to accelerated expansion, with the <span>(f(mathcal{T}))</span> model exhibiting a more dynamic dark energy behavior and an earlier onset of acceleration. These findings suggest that torsional-based gravity may provide a geometrically motivated and observationally consistent alternative to standard cosmology.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 3","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147441279","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Global ionospheric electron density variations observed by F7/C2 and (Sigma mathrm{O}/mathrm{N}_{2}) ratios measured by GUVI during intense geomagnetic storms in solar cycle 25","authors":"Jahan Zeb Khan,&nbsp;Waqar Younas,&nbsp;Christine Amory-Mazaudier,&nbsp;Majid Khan","doi":"10.1007/s10509-026-04559-3","DOIUrl":"10.1007/s10509-026-04559-3","url":null,"abstract":"<div><p>In this study, we investigate the global ionospheric response to the four most intense geomagnetic storms of Solar Cycle 25 (SC 25) by analyzing hourly averaged <span>(Sigma mathrm{O}/mathrm{N}_{2})</span> ratios from the Global Ultraviolet Imager (GUVI) aboard the TIMED satellite, alongside 3D electron density profiles from the FORMOSAT-7/COSMIC-2 (F7/C2) constellation satellites. The analysis focuses on ionospheric behavior at low and mid-latitudes, with further evaluation across three longitudinal sectors: Asia (60°E–120°E), Africa (30°W–60°E), and the Americas (120°W–30°W). The negative effects at mid-latitudes started during the local nighttime in the main phase, prolonged into daytime in the early recovery phase, and continued into the following nighttime. These negative effects also reached low latitudes during similar local times. The extent, intensity, and equatorward expansion of these prolonged negative responses were strongly dependent on storm severity and duration. Short-term positive effects were observed at low latitudes during the early recovery phases of less intense storms. Moreover, positive ionospheric responses were recorded at low and mid-latitudes during daytime in the main phase, and long-lasting positive effects were evident at mid-latitudes during the late recovery phases. This study would be beneficial in enhancing space weather modeling and forecasting capabilities, particularly in understanding ionospheric variability during geomagnetic disturbances.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 3","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147441208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A comparative analysis of solar and geomagnetic activity during different phases of solar cycles 24 and 25","authors":"S. Abila,&nbsp;R. P. Jebin,&nbsp;A. Iren Sobia,&nbsp;M. S. Dhaiya","doi":"10.1007/s10509-026-04549-5","DOIUrl":"10.1007/s10509-026-04549-5","url":null,"abstract":"<div><p>Using hourly data from the OMNIWeb database, we analyze key indices like F10.7 (solar radio flux), Ap, Kp, Dst, and PC (geomagnetic indices) for a few chosen months that represent the solar cycle’s various phases: solar minimum (October 2009), rising phases (August 2010 and December 2022), solar maximum (May 2012), and declining phase (September 2017). Each phase’s unique geomagnetic activity patterns are revealed by our analysis. Only slight disruptions were seen in the solar and geomagnetic activity during the solar minimum. During the rising phase, we saw a steady rise in solar activity, a significant geomagnetic storm in December 2022, and associated improvements in geomagnetic indices. Geomagnetic disruptions were frequent and severe during the solar maximum phase, which was marked by intense and extremely variable solar activity. Moderate geomagnetic activity was detected throughout the falling phase, most likely due to corotating high-speed solar wind streams. This study indicates the statistical analysis of solar parameters like F10.7 index, PC index, AP index, Dst index, KP index.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 3","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147363150","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Formation of second-generation stellar populations in globular clusters: the role of binary stars and stellar collisions","authors":"Suparna Sau,&nbsp;Pratap Ray","doi":"10.1007/s10509-026-04555-7","DOIUrl":"10.1007/s10509-026-04555-7","url":null,"abstract":"<div><p>This paper aims to explore the impact of binary stars on the creation of second generation stellar populations using a model based on stellar collisions. This is accomplished by using a simple model of stellar collisions in which two first-generation stars collide and produce a product star belonging to the second-generation stellar population. Clusters are formed with single and binary stars having masses generated from a truncated Pareto distribution using Monte Carlo simulations and the split core pairing algorithm to form binary stars. No triples or further multiple stars are considered. We have considered single-single and single-binary collisions in our model. Then we studied the correlations between the fraction of second-generation stars and the slope of present-day mass function of the after-collision cluster and have compared those with observed data for 49 galactic globular clusters. We find that the fraction of second-generation stars is positively correlated to the slope of mass function for high-mass clusters and low-mass clusters separately. We additionally explore the possible values of the fraction of binary stars, the fraction of colliding single stars, the fraction of colliding binary stars as well as the slopes of the initial mass generating function that led to the formation of the present day observed high mass and low mass clusters.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 3","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147363220","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Variable red giants exploration with MASTER robotic net: main algorithms and study of three Mira-type targets","authors":"Alexander N. Tarasenkov,&nbsp;Vladimir M. Lipunov,&nbsp;Artem S. Kuznetsov,&nbsp;Gleb A. Antipov,&nbsp;Pavel V. Balanutsa,&nbsp;Nataly V. Tyurina,&nbsp;Yakov Y. Kechin","doi":"10.1007/s10509-026-04553-9","DOIUrl":"10.1007/s10509-026-04553-9","url":null,"abstract":"<div><p>We are discussing the capabilities of MASTER network of robotic telescopes to study variable red giant stars. We report the discovery and present archival light curves for three optical transients, connected with long period variable red giants, based on MASTER Robotic Net all-sky survey observations and archival MASTER light curves at Lomonosov database storage. We demonstrate transient detection frames and light curves for three Mira-type variables: MASTER OT <span>({J083717.54-573411.1})</span>, MASTER OT <span>({J190436.33+192828.7})</span> and MASTER OT <span>({J07010810-6818548})</span>. Spectroscopically validated carbon star MASTER OT <span>({J07010810-6818548})</span> shows mean magnitude growth but constant pulsation period which may indicate the presence of a long secondary period. As the result of MASTER wide-field images analysis at Lomonosov supercomputer data storage we present the 8-years historical light curves for all three objects with period calculations for all three Mira-type variables. We estimated fundamental astrophysical parameters for all three Mira-type variables: luminosities, radii, and zero age main sequence (ZAMS) masses.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 3","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147336522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Parametric resonance scenario for peanut bulge formation in rotating galactic stellar disks","authors":"Evgeny Griv,&nbsp;Asher Yahalom","doi":"10.1007/s10509-026-04552-w","DOIUrl":"10.1007/s10509-026-04552-w","url":null,"abstract":"<div><p>The coupling is established analytically between the natural oscillations of stars normal to the mean horizontal plane and periodic changes in the excitation force in a rotationally flattened galactic disk using a linear perturbation framework. The nonaxisymmetric gravitational potential of a density-wave bar may cause these changes in this ‘pumping’ force. The excitation of out-of-plane oscillating motion with an amplitude exponentially increasing with time via parametric resonance interaction between stars and a bar is considered for the formation of the boxy/peanut-shaped bulges (an X-structure of stars crossing at the center of the system) often observed in disk galaxies, even in isolation, as well as in the Galaxy. A scenario involving this resonant interaction accounts for both the vertically short <span>(lesssim 1)</span> kpc boxy/peanut-shaped features and a <span>(sim 1)</span> Gyr time delay between when the bars form and vertically thicken.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 2","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10509-026-04552-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147341863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Precision cosmology with the lightest elements","authors":"Max Pettini,&nbsp;Ryan Cooke","doi":"10.1007/s10509-026-04551-x","DOIUrl":"10.1007/s10509-026-04551-x","url":null,"abstract":"<div><p>In this brief review, we describe the key role played by Big Bang Nucleosynthesis (BBN) in today’s ‘Precision Cosmology’, focusing in particular on the precise determination of the primordial abundance of deuterium. We describe the development of the ideas and methods of BBN research from their beginnings more than 75 years ago to the latest developments, and conclude with a forward look to likely advances expected towards the end of the current decade.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"371 2","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10509-026-04551-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147341479","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}