International Astronomy and Astrophysics Research Journal

Resolving the Hubble Tension with a Late Dark Energy Modification to the ΛCDM Model

Daniel E. Friedmann — Fri, 17 Jan 2025 00:00:00 +0000

The Hubble tension arises from the difference between direct measurements of the Hubble constant and indirect measurements based on a cosmological model. This discrepancy has been confirmed with increasing precision, suggesting a potential issue with the current cosmological model. The simplest Lambda Cold Dark Matter (ΛCDM) model, which incorporates a cosmological constant associated with dark energy, provides a good fit for a wide range of cosmological data. In this paper, we propose a modification to the ΛCDM model, hypothesizing that dark energy within gravitationally bound structures does not significantly affect the expansion of space within them. We test this hypothesis by modifying the ΛCDM model accordingly. We simulate this modified ΛCDM model and compare it against both direct and indirect measurements of the Hubble constant. Our results indicate that this modification resolves the Hubble tension, providing a strong fit to both direct and indirect measurements of the Hubble constant.

Weather Parameters Influence on Radio Wave Transmission Signals in Some Selected South-Western Parts of Nigeria

Olayinka Joshua Oyewole — Wed, 12 Feb 2025 00:00:00 +0000

Meteorological variables such as water vapor, temperature and atmospheric pressure greatly influence radio signal transmission. In this study, the influence of air temperature variations of some selected locations in the South-Western part of Nigeria on specific attenuation, radio refractivity and water vapour were investigated using the weather parameters obtained from Nigerian Meteorological Agency (NiMeT) for two years (2022 and 2023). The result revealed dependence of specific attenuation on temperature as lower attenuation of 0.047 dB/Km was observed at higher temperature of 28.5^oC. The surface radio refractivity in the sampling areas was found to be higher (372 N-units) during the rainy seasons and lower (247 N-units) during the dry seasons. Also, during the periods of high temperature, the water vapour content in the atmosphere was low (0.62 g/m³) signifying water vapour effects on radio propagation during the days of low temperature. In conclusion, the radio wave transmission signals were influenced by the weather parameters in the examined location.

Variable Stars and Their Implications for Stellar Astrophysics

Anik Shrivastava — Fri, 18 Apr 2025 00:00:00 +0000

The paper provides a review on the relationship between the variation of some stars with certain evolutionary features, with particular emphasis on how stellar pulsations and eruptions aid in the understanding of stellar evolution theories. It analyzes and discusses light curves, spectral classifications, and periodicity measurements of different variable stars to gain a better understanding of the processes that transfer energy and the mechanisms that cause pulsation. Results suggest that certain subclasses of variable stars, especially the Cepheid and the RR Lyrae variable stars, obey some certain trends of mass and luminosity which are very stringent bounds for the existing stellar evolution models. Furthermore, the new modes of pulsations described in this paper are capable of overturning the established paradigms of stellar astrophysics and may define new boundaries of astrophysical research. The paper also emphasizes the importance of the dynamics of stellar populations in the refinement of cosmological models related to the evolution of galaxies and the universe in general, which makes these models more realistic. This work makes a point on the strong correlation between the variability of stars and the profound questions in time, state of equilibrium, and change in the system that is being studied: the dynamics of natural systems.

Stochastic Modeling of Compact Binary Coalescences for Gravitational Wave Analysis

Debasri Samanta, Rajib Kumar Dolai — Wed, 11 Jun 2025 00:00:00 +0000

Aims: To develop a stochastic mathematical framework for modeling gravitational wave signals from Compact Binary Coalescences (CBCs), incorporating uncertainties in mass and spin evolution and improving signal detection and parameter estimation.

Study Design: A simulation-based theoretical study using a stochastic approach to enhance the modeling of gravitational wave signals.

Methodology: The model integrates the inspiral-merger-ringdown (IMR) waveform with stochastic differential equations (SDEs) to represent uncertainties in component evolution due to astrophysical and numerical factors. Monte Carlo simulations are used to analyze probabilistic behavior in mass and spin dynamics. Kalman filtering is applied for tracking evolving parameters in noisy data, while matched filtering and Bayesian inference are employed for signal extraction and posterior parameter estimation. All simulations are implemented in MATLAB.

Results: Simulations show that spin parameters are more sensitive to stochastic fluctuations than mass. Kalman filtering accurately tracks hidden parameters under noisy conditions. Matched filtering effectively identifies weak gravitational wave signals, and Bayesian inference provides well-centered Gaussian posterior distributions, supporting reliable parameter estimation.

Conclusion: The proposed stochastic framework enhances the realism and robustness of gravitational wave modeling from CBCs. By combining stochastic dynamics with advanced filtering and inference techniques, the study demonstrates a comprehensive approach for analyzing signals under uncertain conditions, offering valuable insights for future gravitational wave detection and analysis efforts.

JWST/MIRI Observations of PAH Emission and Evolution in H II Regions of NGC 5457

Atul Kumar Singh, Rahul Kumar Anand, Shantanu Rastogi — Fri, 22 Aug 2025 00:00:00 +0000

Background: PAH emission features in a single observation, allowing for a robust and systematic study of their relative variations without the systematic uncertainties inherent in stitching together data from different instruments or observing modes. This provides a powerful and self-consistent lever for untangling their complex excitation mechanisms and environmental dependencies.

Aims: The present study investigates the physical processing of PAHs in high-mass star-forming environments. This study aims to characterize how the PAH ionization fraction varies across different H II regions and to search for spectroscopic evidence of the processing or destruction of PAH molecules in intense radiation fields.

Methodology: We utilized mid-infrared integral field spectroscopic data from the JWST's Mid-Infrared Instrument (MIRI) in its Medium Resolution Spectroscopy (MRS) mode. One-dimensional spectra were extracted for each of the four H II regions. We measured the integrated fluxes of the prominent PAH emission features at 7.7, 8.6, and 11.3 µm and calculated key diagnostic flux ratios to probe the physical state of the PAH population.

Results: The four H II regions in NGC 5457 exhibit significant diversity in their PAH spectral characteristics. The diagnostic F(8.6)/F(11.3) ratio, a tracer of PAH ionization, varies from 0.23 to 0.62 across the sample. The region with the highest ionization (highest F(8.6)/F(11.3)) shows the lowest F(7.7)/F(8.6) ratio (1.13), while the region with the lowest ionization has the highest F(7.7)/F(8.6) ratio (2.38). The inclusion of the 6.2 µm feature would provide an additional probe of the cation population, while the 17 µm feature would trace the largest, most stable PAHs, providing a more robust anchor for size distribution models. This study demonstrates the immense potential of JWST spectroscopy for dissecting the microphysics of the ISM and motivates such future investigations.

Conclusion: The observed spectral diversity is primarily driven by variations in the PAH ionization state, which is governed by the local radiation field intensity. The strong anti-correlation between the F(7.7)/F(8.6) and F(8.6)/F(11.3) ratios provides a new, powerful diagnostic for PAH processing. This trend is interpreted as an evolutionary sequence where increasingly harsh radiation fields not only ionize the PAH population but also alter the surviving cations, consistent with the selective destruction of the carriers of the 7.7 µm feature.

Planetary Ionospheres and Ionospheric Instabilities

S. J. Gogoi — Thu, 27 Feb 2025 00:00:00 +0000

Over the several decades’ degree of theoretical and experimental investigations on the Planetary ionospheres have continued to escalate in different aspects. Studying the mechanics of ionospheric events is essential to comprehending space weather, its effects on planetary atmospheres, and its instabilities. Usually, such physics entails simulating ionosphere dynamics. Ionospheric region has weak particle collision rate and weak magnetic field strength gradient. Primary Solar wind and other secondary cosmic sources are the main sources of energy and momenta to this open plasma system. These regions have many linear and nonlinear properties for the energy exchange among waves and particles. Complex radiation emission phenomena are observed in different altitudes of terrestrial ionospheric regions by ground based and satellite based observatories. In this note, characteristics of ionospheric plasma and various instabilities which are observed in this domain are discussed which are helpful for near Earth space environment.

Exomoons and Exorings: Detection, Formation and Habitability under the Influence of Gamma-Ray Bursts

Himanshu Bansal, Ritika Raj, K Yeshaswini, Himanshi Sharma, Riddhi Dakhole — Fri, 05 Dec 2025 00:00:00 +0000

The study of exomoons and exorings represents a growing frontier in exoplanetary science, illuminating planetary formation, system evolution, and the search for habitable environments beyond Earth. Although no confirmed exomoons have yet been identified, advances in transit timing and duration variations, direct imaging, astrometry, radial velocity, and microlensing have improved detection sensitivity. This review consolidates advances in detection strategies, moon and ring formation theory, and astrophysical habitability contexts, emphasising the vulnerability and resilience of exomoons and exorings to GRB exposure. By linking detection feasibility to GRB-conditioned habitability priors, it presents a unified framework bridging planetary science, astrophysics, and astrobiology. Theoretical models predict diverse and stable moon systems with typical satellite-to-planet mass ratios of ∼ 10−4, many capable of sustaining habitable conditions through tidal heating, magnetic shielding, and subsurface oceans. Exorings, inferred from asymmetric transit light curves and forward-scattering signals, offer diagnostic insight into circumplanetary disk evolution and angular momentum processes. Their survivability, however, remains uncertain under the influence of stellar radiation, collisions, and magnetic drag. Gamma-ray bursts (GRBs), delivering fluences of ∼ 10–100 kJm⁻², can erode atmospheres, deplete ozone layers, and perturb climates, imposing episodic but severe constraints on long-term habitability.

Determining Latent Anisotropy Inherent in the Two-way Propagation of Light in Vacuum: A Conceptual Approach

Mark A. Tarbell — Tue, 02 Sep 2025 00:00:00 +0000

Aims: The propagation of light in vacuo has generally been assumed to be isotropic; i.e., its recessional velocity is assumed to be identical with its return speed back to the observer. This article presents a novel conceptual approach to this fundamental yet unresolved issue in physics: Is light propagation isotropic? The synchronization of mutually-distant time clocks has long been the bane of speed of light measurements. If such synchronization can be achieved at arbitrarily large or even astronomical scales, it can lay the foundation for methods to directly measure the one-way speed of light. Building upon this basis, any potential latent anisotropy which may be inherent in the propagation of light can then be investigated, both terrestrially and between the Earth and Moon or other planetary bodies.

Methodology: We propose methods whereby mutually distant (unsynchronized) atomic clocks are positioned on the Earth and the Moon. The clocks are devised to receive a set of signals transmitted from a man-made satellite or probe positioned at great mutual distance to the clocks and outside the ecliptic plane. The satellite emits electromagnetic timing signals (RF/laser); these signals serve as remote common external events to the atomic clocks. The clocks set themselves simultaneously to these signals, and are thereby synchronized by the same distantly-sourced external event(s).

Conclusion: Many novel and technically intricate speed of light measurement methodologies have been devised to measure, directly or indirectly, the speed of light between two points, with varying degrees of accuracy and reliability. However, none has yet shown promise to scale to astronomical distances. Practical experimental schemes are put forth herein for synchronizing mutually-distant atomic clocks. This allows for the direct measurement of the one-way speed of light, a feat which has never been accomplished definitively. Measurements of this nature could provide direct evidence to support or undermine the cosmological principle, with far-reaching ramifications.

A Topographic Perspective on Jupiter’s Great Red Spot: Insights from Ocean Circulation Models

John A. T. Bye — Tue, 28 Jan 2025 00:00:00 +0000

In a recent study using an Ocean General Circulation Model (OGCM) it was shown that the forcing by the surface vertical velocity generated a significant vorticity to that generated by the curl of the wind stress forcing. On Jupiter the surface vertical velocity is the only source of vorticity, and the Coriolis force is very similar to that in the sub-tropics on Earth. This leads to a plausible mechanism for the existence of the Great Red Spot (GRS) which is investigated in this paper. The properties which are modelled include the topography of the GRS, which is predicted to be a tabletop mountain of probable height about 1 km, situated on a surrounding gently sloping plain extending outwards over approximately 2000 km. On this plain, the upward vertical velocity brings fluid to the surface, where we propose it is trapped in a fluidic mixed layer probably of a few meters thickness beneath the intensely cold icy cap. This is analogous to the formation of a mixed layer in the oceans on Earth The time scale for heat exchange with the atmosphere is probably about 10 hrs, similar to the rotation period of Jupiter.

Supermassive Black Holes and Galactic Evolution: Insights from Observations and Simulations

Anik Shrivastava — Mon, 21 Apr 2025 00:00:00 +0000

Black holes are regions of spacetime characterized by exceptionally strong gravitational forces that inhibit the escape of matter or radiation, rendering them among the most enigmatic phenomena in astronomy. This work offers an in-depth analysis of the role of black holes in galaxy evolution, with specific emphasis on the interaction between supermassive black holes (SMBHs) and their host galaxies. An essential element of this interaction is the function of active galactic nuclei (AGN), wherein accreting supermassive black holes (SMBHs) emit substantial energy, affecting star formation, gas dynamics, and extensive galactic structures. AGN-driven feedback, via powerful jets, radiation pressure, and outflows, can either initiate or inhibit star formation, significantly influencing galaxy growth regulation. Comprehending the coevolution of galaxies and their central black holes, especially regarding AGN activity, offers profound insights into the evolutionary forces that mould the universe.