Universe最新文献_第5页

Hot Stars, Young Stellar Populations and Dust with Swift/UVOT 热恒星、年轻恒星群和尘埃与 Swift/UVOT

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-16 DOI: 10.3390/universe10080330

Michael H. Siegel, Caryl Gronwall

{"title":"Hot Stars, Young Stellar Populations and Dust with Swift/UVOT","authors":"Michael H. Siegel, Caryl Gronwall","doi":"10.3390/universe10080330","DOIUrl":"https://doi.org/10.3390/universe10080330","url":null,"abstract":"In this review, we highlight the contributions made by the Swift/UVOT instrument to the understanding of the ultraviolet (UV) attenuation and extinction properties of interstellar dust and provide insight into hot stars and young stellar populations. The study of these two fields is interconnected: UV-bright objects can only be understood if the effects of foreground dust are accounted for, but foreground dust can only be accounted for by studying the properties of UV-bright objects. Decades worth of work have established that the effects of dust on background starlight vary in the ultraviolet, with proposed extinction laws having a wide variety of slopes and a strong “bump” spectroscopic feature at 2175 Å. We show that UVOT is uniquely suited to probe variations in the UV extinction law, specifically because of the uvm2 filter that is centered on the bump and the telescope’s ability to resolve nearby stellar populations. When used in combination with optical and infrared imaging, UVOT can provide strong constraints on variations in the extinction law, both from galaxy to galaxy and within individual galaxies, as well as the properties of young stellar populations. Surveys of UVOT have included the Milky Way, the galaxies of the Local Group, the Local Volume Legacy Survey (LVLS) and two deep fields. All of these are being utilized to provide the most detailed information yet about the UV dust attenuation law and the connection of its variation to underlying physical processes as well as the UV properties of hot stars and young stellar populations.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"44 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210918","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}

引用次数: 0

Weak Deflection Angle by the Einstein–Cartan Traversable Wormhole Using Gauss–Bonnet Theorem with Time Delay 利用高斯-波内特定理和时间延迟计算爱因斯坦-卡尔坦可穿越虫洞的弱偏转角

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-16 DOI: 10.3390/universe10080331

Susmita Sarkar, Nayan Sarkar, Abhisek Dutta, Farook Rahaman

{"title":"Weak Deflection Angle by the Einstein–Cartan Traversable Wormhole Using Gauss–Bonnet Theorem with Time Delay","authors":"Susmita Sarkar, Nayan Sarkar, Abhisek Dutta, Farook Rahaman","doi":"10.3390/universe10080331","DOIUrl":"https://doi.org/10.3390/universe10080331","url":null,"abstract":"In this article, we estimate the gravitational deflection angles of light in the spacetime of Einstein–Cartan wormholes supported by normal matter or phantom energy utilizing the Gauss–Bonnet theorem. The obtained deflection angles are examined in relation to the wormhole throat radius r0 and the equation of state parameter ω across four scenarios, and it has been seen that the larger throat radii r0 result in higher deflection angles. Moreover, the wormholes filled with phantom energy exhibit greater deflection angles compared to those filled with normal matter. The reported deflection angles are influenced by dark matter and Maxwell’s fish eye matter: Dark matter, as well as Maxwell’s fish eye matter, increases the deflection angles. The deflection angle is also estimated using the Keeton and Petters method, which is proportional to wormhole throat r0 and inversely proportional to the impact parameter b. Additionally, a comparative study is performed on the deflection angles obtained from four different scenarios. Finally, analytical results for time delay due to Einstein–Cartan wormholes are estimated for the four ω cases which are decreasing for increasing values of rc.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"67 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210917","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}

引用次数: 0

Convolutional Neural Network Processing of Radio Emission for Nuclear Composition Classification of Ultra-High-Energy Cosmic Rays 卷积神经网络处理超高能量宇宙射线核成分分类中的无线电辐射

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-15 DOI: 10.3390/universe10080327

Tudor Alexandru Calafeteanu, Paula Gina Isar, Emil Ioan Sluşanschi

{"title":"Convolutional Neural Network Processing of Radio Emission for Nuclear Composition Classification of Ultra-High-Energy Cosmic Rays","authors":"Tudor Alexandru Calafeteanu, Paula Gina Isar, Emil Ioan Sluşanschi","doi":"10.3390/universe10080327","DOIUrl":"https://doi.org/10.3390/universe10080327","url":null,"abstract":"Ultra-high-energy cosmic rays (UHECRs) are extremely rare energetic particles of ordinary matter in the Universe, traveling astronomical distances before reaching the Earth’s atmosphere. When primary cosmic rays interact with atmospheric nuclei, cascading extensive air showers (EASs) of secondary elementary particles are developed. Radio detectors have proven to be a reliable method for reconstructing the properties of EASs, such as the shower’s axis, its energy, and its maximum (Xmax). This aids in understanding fundamental astrophysical phenomena, like active galactic nuclei and gamma-ray bursts. Concurrently, data science has become indispensable in UHECR research. By applying statistical, computational, and deep learning methods to both real-world and simulated radio data, researchers can extract insights and make predictions. We introduce a convolutional neural network (CNN) architecture designed to classify simulated air shower events as either being generated by protons or by iron nuclei. The classification achieved a stable test error of 10%, with Accuracy and F1 scores of 0.9 and an MCC of 0.8. These metrics indicate strong prediction capability for UHECR’s nuclear composition, based on data that can be gathered by detectors at the world’s largest cosmic rays experiment on Earth, the Pierre Auger Observatory, which includes radio antennas, water Cherenkov detectors, and fluorescence telescopes.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"6 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227850","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}

引用次数: 0

From the Janis–Newman–Winicour Naked Singularities to the Einstein–Maxwell Phantom Wormholes 从杰尼斯-纽曼-维尼库尔裸奇点到爱因斯坦-麦克斯韦尔幽灵虫洞

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-15 DOI: 10.3390/universe10080328

Changjun Gao, Jianhui Qiu

{"title":"From the Janis–Newman–Winicour Naked Singularities to the Einstein–Maxwell Phantom Wormholes","authors":"Changjun Gao, Jianhui Qiu","doi":"10.3390/universe10080328","DOIUrl":"https://doi.org/10.3390/universe10080328","url":null,"abstract":"The Janis–Newman–Winicour spacetime corresponds to a static spherically symmetric solution of Einstein equations with the energy momentum tensor of a massless quintessence field. It is understood that the spacetime describes a naked singularity. The solution has two parameters, b and s. To our knowledge, the exact physical meaning of the two parameters is still unclear. In this paper, starting from the Janis–Newman–Winicour naked singularity solution, we first obtain a wormhole solution by a complex transformation. Then, letting the parameter s approach infinity, we obtain the well-known exponential wormhole solution. After that, we embed both the Janis–Newman–Winicour naked singularity and its wormhole counterpart in the background of a de Sitter or anti-de Sitter universe with the energy momentum tensor of massive quintessence and massive phantom fields, respectively. To our surprise, the resulting quintessence potential is actually the dilaton potential found by one of us. It indicates that, by modulating the parameters in the charged dilaton black hole solutions, we can obtain the Janis–Newman–Winicour solution. Furthermore, a charged wormhole solution is obtained by performing a complex transformation on the charged dilaton black hole solutions in the background of a de Sitter or anti-de Sitter universe. We eventually find that s is actually related to the coupling constant of the dilaton field to the Maxwell field and b is related to a negative mass for the dilaton black holes. A negative black hole mass is physically forbidden. Therefore, we conclude that the Janis–Newman–Winicour naked singularity solution is not physically allowed.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"58 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210919","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}

引用次数: 0

Multi-Messenger Connection in High-Energy Neutrino Astronomy 高能中微子天文学中的多信使联系

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-13 DOI: 10.3390/universe10080326

Ankur Sharma

引用次数: 0

Constraint on the Cosmic Curvature in a Model with the Schwarzschild–de Sitter Metric from Supernovae and Gamma-Ray Burst Observational Data 从超新星和伽马射线暴观测数据看施瓦兹希尔德-德-西特公设模型中的宇宙曲率约束

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-11 DOI: 10.3390/universe10080325

Vladimir N. Yershov

{"title":"Constraint on the Cosmic Curvature in a Model with the Schwarzschild–de Sitter Metric from Supernovae and Gamma-Ray Burst Observational Data","authors":"Vladimir N. Yershov","doi":"10.3390/universe10080325","DOIUrl":"https://doi.org/10.3390/universe10080325","url":null,"abstract":"In developing his cosmological model of 1917, de Sitter theoretically predicted the phenomenon of cosmological redshift (the de Sitter effect), which he did long before the discovery of this phenomenon in observations. The de Sitter effect is gravitational by its nature, as it is due to differences between the coordinate systems of the observer and the distant source. However, the relationship between the redshift and distance derived from the de Sitter metric is at odds with observations, since this relationship is nonlinear (quadratic) for small redshifts, while the observed relationship between the same quantities is strictly linear. This paper discusses the possibility that cosmological redshift is gravitational by its nature, as in de Sitter’s 1917 model. At the same time, here, as in de Sitter’s model, an elliptical space is used, the main characteristic of which is the identification of its antipodal points. But, unlike de Sitter’s model, here, in order to ensure strict linear dependence of the redshift on distance, the origin of the reference system is transferred to the observer’s antipodal point. The Schwarzschild–de Sitter metric used in this model allows you to estimate the curvature of space from observational data. To achieve this, a theoretical Hubble diagram is built within the framework of the model with the Schwarzschild–de Sitter metric, which is compared with observations from the Pantheon+ catalogue of type Ia supernovae and the Amati catalogue of gamma-ray bursts in the redshift range of 0<z<8. As a result of this comparison, we found that the lower estimate of the radius of curvature of space was quite large: 2.4×1015 Mpc. This means that the observational data indicate a negligible curvature of space.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"5 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940634","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}

引用次数: 0

Coupled Quintessence Inspired by Warm Inflation 受暖膨胀启发的耦合昆体

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-10 DOI: 10.3390/universe10080324

Paulo M. Sá

引用次数: 0

Strange Dwarfs: A Review on the (in)Stability 奇怪的矮人关于（不）稳定性的评论

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-09 DOI: 10.3390/universe10080322

Francesco Di Clemente, Alessandro Drago, Giuseppe Pagliara

引用次数: 0

Revisiting Quantum Field Theory in Rindler Spacetime with Superselection Rules 用超选规则重温林德勒时空中的量子场论

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-08 DOI: 10.3390/universe10080320

K. Sravan Kumar, João Marto

{"title":"Revisiting Quantum Field Theory in Rindler Spacetime with Superselection Rules","authors":"K. Sravan Kumar, João Marto","doi":"10.3390/universe10080320","DOIUrl":"https://doi.org/10.3390/universe10080320","url":null,"abstract":"Quantum field theory (QFT) in Rindler spacetime is a gateway to understanding unitarity and information loss paradoxes in curved spacetime. Rindler coordinates map Minkowski spacetime onto regions with horizons, effectively dividing accelerated observers into causally disconnected sectors. Employing standard quantum field theory techniques and Bogoliubov transformations between Minkowski and Rindler coordinates yields entanglement between states across these causally separated regions of spacetime. This results in a breakdown of unitarity, implying that information regarding the entangled partner may be irretrievably lost beyond the Rindler horizon. As a consequence, one has a situation of pure states evolving into mixed states. In this paper, we introduce a novel framework for comprehending this phenomenon using a recently proposed formulation of direct-sum quantum field theory (DQFT), which is grounded in superselection rules formulated by the parity and time reversal (PT) symmetry of Minkowski spacetime. In the context of DQFT applied to Rindler spacetime, we demonstrate that each Rindler observer can, in principle, access pure states within the horizon, thereby restoring unitarity. However, our analysis also reveals the emergence of a thermal spectrum of Unruh radiation. This prompts a reevaluation of entanglement in Rindler spacetime, where we propose a novel perspective on how Rindler observers may reconstruct complementary information beyond the horizon. Furthermore, we revisit the implications of the Reeh-Schlieder theorem within the framework of DQFT. Lastly, we underscore how our findings contribute to ongoing efforts aimed at elucidating the role of unitarity in quantum field theory within the context of de Sitter and black hole spacetimes.","PeriodicalId":48646,"journal":{"name":"Universe","volume":"372 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940748","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}

引用次数: 0

Lifetime of Long-Lived Sunspot Groups 长寿命太阳黑子群的寿命

IF 2.9 4区物理与天体物理

Universe Pub Date : 2024-08-05 DOI: 10.3390/universe10080318

Judit Muraközy

引用次数: 0