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Research Article
Revisiting Oxygen Production Pathways: 16O Abundances in 34 Metal-Poor Stars
Issue:
Volume 13, Issue 1, March 2026
Pages:
1-14
Received:
10 December 2025
Accepted:
23 December 2025
Published:
4 February 2026
Abstract: We investigate how the oxygen isotope 16O is produced in metal-poor stars and whether current nuclear reaction models can explain the oxygen abundances observed in such stars. Our study focuses on proton- and α-capture reactions operating within the Carbon–Oxygen–Fluorine (COF) nuclear reaction chain, using updated reaction rates from recent nuclear physics compilations. Oxygen abundances are calculated under representative stellar conditions and compared with observational measurements for a sample of 34 metal-poor halo and thick-disk stars taken from the literature. The results show that there exists a limited range of stellar temperatures for which the calculated oxygen abundances closely match the observed values. At relatively low temperatures, the oxygen abundance remains nearly constant, indicating that oxygen production and destruction are both inefficient. As the temperature increases beyond about 0.15 GK, oxygen production becomes more effective, leading to an increase in the predicted oxygen abundance. At still higher temperatures, competing nuclear reactions reduce the net amount of oxygen produced, causing the abundance to decline. A statistical comparison between the calculated and observed oxygen abundances shows a strong agreement, with a correlation coefficient of r = 0.89. For most stars, the differences between predicted and observed values are small and lie within the uncertainties expected from spectroscopic measurements. The few cases where larger differences are found can be explained by observational uncertainties and stellar mixing processes. Overall, our results indicate that the COF nuclear reaction chain provides a consistent explanation for oxygen production in low-mass, metal-poor stars and plays an important role in shaping the chemical evolution of the early Galaxy.
Abstract: We investigate how the oxygen isotope 16O is produced in metal-poor stars and whether current nuclear reaction models can explain the oxygen abundances observed in such stars. Our study focuses on proton- and α-capture reactions operating within the Carbon–Oxygen–Fluorine (COF) nuclear reaction chain, using updated reaction rates from recent nuclea...
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Review Article
Study of Important Space Missions and Evaluation of Discovering the Astonishing Universe
Khandakar Akhter Hossain*
Issue:
Volume 13, Issue 1, March 2026
Pages:
15-31
Received:
24 December 2025
Accepted:
16 January 2026
Published:
6 February 2026
Abstract: The evaluation of space missions and their influence on the understanding of universe is complicated. They provide both scientific data and insights along with inspire inquisitiveness and fostering a sense of sensation about the cosmos. It has started with the space race of the 20th century, as a result of humans have boarded on a journey through time and space with some of the most groundbreaking and life-changing space missions. NASA’s astrophysics division is dedicated to exploring the universe, pushing the boundaries of what is known of the cosmos, and sharing its discoveries with the world. The division continues growing humanity’s understanding of how the universe began and progressed. NASA researchers are making advancement towards addressing the appealing questions of life in the universe, the early beginnings of the universe, and how it all works with leading-edge technologies and groundbreaking science. The Apollo missions, was a great attempt of courage in human civilization; not only landed humans on the Moon but also brought back samples that helped scientists understand lunar geology and planetary science. The Hubble Space Telescope has revolutionized astronomy, offering fabulous images of distant galaxies and nebulae, and has led to groundbreaking discoveries like the measurement of the universe's expansion rate and the identification of exoplanets. Mars rover missions have advanced our understanding of alien geology and climate, paving the way for future human missions to the red planet. These missions have not only transformed how we see the universe but also describe how we live on earth, contributing to our understanding of the solar system and beyond. Astronomers recently spotted this black hole’s flare-up through XMM-Newton and XRISM’s X-ray technology and noted that it appeared to fade quickly, creating the fast-moving winds. It is a review article to explore and appraise the important space missions on the basis of historical evidence and evaluating the urge of discovering mind set to know the multifaceted cosmology and astonishing Universe.
Abstract: The evaluation of space missions and their influence on the understanding of universe is complicated. They provide both scientific data and insights along with inspire inquisitiveness and fostering a sense of sensation about the cosmos. It has started with the space race of the 20th century, as a result of humans have boarded on a journey through t...
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Research Article
The Effects of the Geomagnetic Storm of October 2024 on the African Ionosphere
Issue:
Volume 13, Issue 1, March 2026
Pages:
32-44
Received:
17 November 2025
Accepted:
1 December 2025
Published:
18 March 2026
DOI:
10.11648/j.ajaa.20261301.13
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Views:
Abstract: This study investigates the ionospheric response over the equatorial and low-latitude regions in African during the geomagnetic storm that occurred on 10–11 October 2024. In order to investigate the ionospheric response to geomagnetic storms of varying intensities, a detailed study of vertical Total Electron Content (TEC) variations resulting from Global Navigation Satellite System (GNSS) and International Reference Ionosphere 2020 (IRI2020) data acquired at the Africa sector has been carried out in this work. The data used include GNSS measurements from International GNSS Service (IGS) African eight stations, IRI2020 model, O/N2 ratio information obtained by the Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI), magnetometer data, and an ionospheric electric fields model. The integrity of GNSS is critically dependent on the state of the Earth’s ionosphere. During space weather events like geomagnetic storms, the ionosphere can become highly disturbed, leading to signal scintillations and severe degradation of navigation reliability. The deviation in TEC was used to observe the ionospheric storm effects. The results show both positive enhancements and negative depletions in TEC across the stations during the events. The findings reveal significant TEC enhancements over the Yamoussoukro (YKRO) and Lusaka (ZAMB) stations, while reductions were observed at the Antananarivo (ABPO), Addis Ababa (ADIS), Djibouti (DJIG), Malindi (MAL2), Mafikeng (MFKG), and N’Koltang (NKLG) stations during the storm’s main phase. During the recovery phase, an increase in TEC was observed at the ADIS and DJIG stations, whereas depletions occurred at the other stations. This study used correlation coefficients (r) and root mean square errors (RMSE) to examine the variation of the IRI-2020 TEC from the Global Positioning System (GPS) TEC during the storm. The results show that the model performs better at some stations (ABPO, MFKG, ZAMB) but underestimates at others (ADIS, DJIG, YKRO). Analysis of the magnetometer data indicates that the H component of the magnetic field experiences a larger disturbance at Keetmanshoop (KMH) than at Hermanus (HER). These results provide crucial insights into storm-time electrodynamics over equatorial and low-latitude regions of Africa and highlight the vulnerability of regional navigation systems.
Abstract: This study investigates the ionospheric response over the equatorial and low-latitude regions in African during the geomagnetic storm that occurred on 10–11 October 2024. In order to investigate the ionospheric response to geomagnetic storms of varying intensities, a detailed study of vertical Total Electron Content (TEC) variations resulting from ...
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Research Article
Stratification and Related Ideas for Understanding the Smoothness of Black Hole Horizons
Issue:
Volume 13, Issue 1, March 2026
Pages:
45-58
Received:
3 February 2026
Accepted:
14 February 2026
Published:
18 March 2026
DOI:
10.11648/j.ajaa.20261301.14
Downloads:
Views:
Abstract: In recent work by the author it was found that there is an absence of diffeomorphism symmetry for black hole horizons constrained by the causal structure of spacetime. This absence puts stringent constraints on the black hole spacetime manifold, topology, and smoothness. In particular, it suggests that such manifolds may have only continuity of data but no differentiability. In mathematics, this is described as a spacetime manifold with a C0 structure, and the assumption of smoothness as a C∞ structure might not hold. Previously, we supposed that the spacetime manifold may have a Finsler structure and might not be a homogeneous manifold, thus requiring new insights to study black hole spacetime. Investigating the spacetime manifold picture, we presume a mathematical concept called stratification of spacetime with smooth gluing of manifold data as an essential criterion for understanding the topology of black hole spacetime. In basic terms, stratification is a way of gluing spacetime into a collection of disjoint regions called strata such that the strata themselves are smooth, but the whole manifold may or may not have a differentiable structure. The topology of the spacetime manifold then depends on the criteria used for the process called stratification of spacetime. We investigate these and relatable ideas further in this paper. For smooth readability, we have referenced relevant literature grouped by topics or subtopics throughout the text.
Abstract: In recent work by the author it was found that there is an absence of diffeomorphism symmetry for black hole horizons constrained by the causal structure of spacetime. This absence puts stringent constraints on the black hole spacetime manifold, topology, and smoothness. In particular, it suggests that such manifolds may have only continuity of dat...
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