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Landau Tidal Damping and Major-Body Clustering in Solar and Extrasolar Subsystems 太阳系和太阳系外子系统中的朗道潮汐阻尼和主要天体集群
Astronomy Pub Date : 2024-06-04 DOI: 10.3390/astronomy3020010
D. Christodoulou, D. Kazanas
{"title":"Landau Tidal Damping and Major-Body Clustering in Solar and Extrasolar Subsystems","authors":"D. Christodoulou, D. Kazanas","doi":"10.3390/astronomy3020010","DOIUrl":"https://doi.org/10.3390/astronomy3020010","url":null,"abstract":"Major (exo)planetary and satellite bodies seem to concentrate at intermediate areas of the radial distributions of all the objects orbiting in each (sub)system. We show that angular-momentum transport during secular evolution of (exo)planets and satellites necessarily results in the observed intermediate accumulation of the massive objects. We quantify the ‘middle’ as the mean of mean motions (orbital angular velocities) when three or more massive objects are involved. Radial evolution of the orbits is expected to be halted when the survivors settle near mean-motion resonances and angular-momentum transfer between them ceases (gravitational Landau damping). This dynamical behavior is opposite in direction to what has been theorized for viscous and magnetized accretion disks, in which gas spreads out and away from either side of any conceivable intermediate area. We present angular momentum transfer calculations in few-body systems, and we also calculate the tidal dissipation timescales and the physical properties of the mean tidal field in planetary and satellite (sub)systems.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"7 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141267832","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Deep Sky Objects Detection with Deep Learning for Electronically Assisted Astronomy 利用深度学习检测深空天体，实现电子辅助天文学
Astronomy Pub Date : 2024-05-13 DOI: 10.3390/astronomy3020009
Olivier Parisot, Mahmoud Jaziri
{"title":"Deep Sky Objects Detection with Deep Learning for Electronically Assisted Astronomy","authors":"Olivier Parisot, Mahmoud Jaziri","doi":"10.3390/astronomy3020009","DOIUrl":"https://doi.org/10.3390/astronomy3020009","url":null,"abstract":"Electronically Assisted Astronomy is a fascinating activity requiring suitable conditions and expertise to be fully appreciated. Complex equipment, light pollution around urban areas and lack of contextual information often prevents newcomers from making the most of their observations, restricting the field to a niche expert audience. With recent smart telescopes, amateur and professional astronomers can capture efficiently a large number of images. However, post-hoc verification is still necessary to check whether deep sky objects are visible in the produced images, depending on their magnitude and observation conditions. If this detection can be performed during data acquisition, it would be possible to configure the capture time more precisely. While state-of-the-art works are focused on detection techniques for large surveys produced by professional ground-based observatories, we propose in this paper several Deep Learning approaches to detect celestial targets in images captured with smart telescopes, with a F1-score between 0.4 and 0.62 on test data, and we experimented them during outreach sessions with public in Luxembourg Greater Region.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"6 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140985298","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Constraining the Inner Galactic DM Density Profile with H.E.S.S. 用 H.E.S.S 制约银河系内部 DM 密度剖面
Astronomy Pub Date : 2024-04-11 DOI: 10.3390/astronomy3020008
J. Zuriaga-Puig
{"title":"Constraining the Inner Galactic DM Density Profile with H.E.S.S.","authors":"J. Zuriaga-Puig","doi":"10.3390/astronomy3020008","DOIUrl":"https://doi.org/10.3390/astronomy3020008","url":null,"abstract":"In this short review, corresponding to a talk given at the conference “Cosmology 2023 in Miramare”, we combine an analysis of five regions observed by H.E.S.S. in the Galactic Center, intending to constrain the Dark Matter (DM) density profile in a WIMP annihilation scenario. For the analysis, we include the state-of-the-art Galactic diffuse emission Gamma-optimized model computed with DRAGON and a wide range of DM density profiles from cored to cuspy profiles, including different kinds of DM spikes. Our results are able to constrain generalized NFW profiles with an inner slope γ≳1.3. When considering DM spikes, the adiabatic spike is completely ruled out. However, smoother spikes given by the interactions with the bulge stars are compatible if γ≲0.8, with an internal slope of γsp-stars=1.5.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"23 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140714844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Cosmography of the Minimally Extended Varying Speed-of-Light Model 最小扩展光速变化模型宇宙学
Astronomy Pub Date : 2024-04-07 DOI: 10.3390/astronomy3020007
Seokcheon Lee
{"title":"Cosmography of the Minimally Extended Varying Speed-of-Light Model","authors":"Seokcheon Lee","doi":"10.3390/astronomy3020007","DOIUrl":"https://doi.org/10.3390/astronomy3020007","url":null,"abstract":"Cosmography, as an integral branch of cosmology, strives to characterize the Universe without relying on pre-determined cosmological models. This model-independent approach utilizes Taylor series expansions around the current epoch, providing a direct correlation with cosmological observations and the potential to constrain theoretical models. Various observable quantities in cosmology can be described as different combinations of cosmographic parameters. Furthermore, one can apply cosmography to models with a varying speed of light. In this case, the Hubble parameter can be expressed by the same combination of cosmographic parameters for both the standard model and varying speed-of-light models. However, for the luminosity distance, the two models are represented by different combinations of cosmographic parameters. Hence, luminosity distance might provide a method to constrain the parameters in varying speed-of-light models.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"6 17","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140732641","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Refracted Gravity Solutions from Small to Large Scales 从小尺度到大尺度的折射重力解决方案
Astronomy Pub Date : 2024-04-05 DOI: 10.3390/astronomy3020006
V. Cesare
{"title":"Refracted Gravity Solutions from Small to Large Scales","authors":"V. Cesare","doi":"10.3390/astronomy3020006","DOIUrl":"https://doi.org/10.3390/astronomy3020006","url":null,"abstract":"If visible matter alone is present in the Universe, general relativity (GR) and its Newtonian weak field limit (WFL) cannot explain several pieces of evidence, from the largest to the smallest scales. The most investigated solution is the cosmological model Λ cold dark matter (ΛCDM), where GR is valid and two dark components are introduced, dark energy (DE) and dark matter (DM), to explain the ∼70% and ∼25% of the mass–energy budget of the Universe, respectively. An alternative approach is provided by modified gravity theories, where a departure of the gravity law from ΛCDM is assumed, and no dark components are included. This work presents refracted gravity (RG), a modified theory of gravity formulated in a classical way where the presence of DM is mimicked by a gravitational permittivity ϵ(ρ) monotonically increasing with the local mass density ρ, which causes the field lines to be refracted in small density environments. Specifically, the flatter the system the stronger the refraction effect and thus, the larger the mass discrepancy if interpreted in Newtonian gravity. RG presented several encouraging results in modelling the dynamics of disk and elliptical galaxies and the temperature profiles of the hot X-ray emitting gas in galaxy clusters and a covariant extension of the theory seems to be promising.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"41 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140737453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
A Critical Examination of the Standard Cosmological Model: Toward a Modified Framework for Explaining Cosmic Structure Formation and Evolution 对标准宇宙学模型的批判性审视：建立一个解释宇宙结构形成和演化的修正框架
Astronomy Pub Date : 2024-03-12 DOI: 10.3390/astronomy3010005
Robert Nyakundi Nyagisera, Dismas Wamalwa, Bernard Rapando, Celline Awino, M. Mageto
{"title":"A Critical Examination of the Standard Cosmological Model: Toward a Modified Framework for Explaining Cosmic Structure Formation and Evolution","authors":"Robert Nyakundi Nyagisera, Dismas Wamalwa, Bernard Rapando, Celline Awino, M. Mageto","doi":"10.3390/astronomy3010005","DOIUrl":"https://doi.org/10.3390/astronomy3010005","url":null,"abstract":"This paper explores the fundamental cosmological principle, with a specific focus on the homogeneity and isotropy assumptions inherent in the Friedmann model that underpins the standard model. We propose a modified redshift model that is based on the spatial distribution of luminous matter, examining three key astronomical quantities: light intensity, number density, and the redshift of galaxies. Our analysis suggests that the model can account for cosmic accelerated expansion without the need for dark energy in the equations. Both simulations and analytical solutions reveal a unique pattern in the formation and evolution of cosmic structures, particularly in galaxy formation. This pattern shows a significant burst of activity between redshifts 0 < z < 0.4, which then progresses rapidly until approximately z ≈ 0.9, indicating that the majority of cosmic structures were formed during this period. Subsequently, the process slows down considerably, reaching a nearly constant rate until around z ≈ 1.6, after which a gradual decline begins. We also observe a distinctive redshift transition around z ≈ 0.9 before the onset of dark-matter-induced accelerated expansion. This transition is directly related to the matter density and is dependent on the geometry of the universe. The model’s ability to explain cosmic acceleration without requiring fine tuning of the cosmological constant highlights its novelty, providing a fresh perspective on the dynamic evolution of the universe.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"22 9","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140248919","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Gravity on a Large Scale—Does It Necessarily Look like It Does on a Small Scale? 大尺度的万有引力--是否一定像小尺度的万有引力一样？
Astronomy Pub Date : 2024-03-01 DOI: 10.3390/astronomy3010004
Jerzy Kijowski
{"title":"Gravity on a Large Scale—Does It Necessarily Look like It Does on a Small Scale?","authors":"Jerzy Kijowski","doi":"10.3390/astronomy3010004","DOIUrl":"https://doi.org/10.3390/astronomy3010004","url":null,"abstract":"The notion of a local inertial reference frame is thoroughly analyzed. Dynamics of a field of such frames is derived from the variational principle. It is shown that the resulting theory splits naturally into three sectors, one of which is purely gravitational. Field dynamics in this sector, equivalent to Einstein’s vacuum equations, is obtained unambiguously and admits no ad hoc corrections. The cosmological constant is an essential element of this construction and cannot be removed. It has been shown that the second sector of this theory corresponds to electrodynamics, while the last sector could possibly describe dark matter.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"29 18","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140084211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Possible Tests of Fundamental Physics with GINGER 用 GINGER 对基础物理学进行可能的测试
Astronomy Pub Date : 2024-02-29 DOI: 10.3390/astronomy3010003
G. Di Somma, C. Altucci, F. Bajardi, Andrea Basti, N. Beverini, Salvatore Capozziello, G. Carelli, Simone Castellano, D. Ciampini, Gaetano De Luca, A. D. Di Virgilio, F. Fuso, Francesco Giovinetti, E. Maccioni, Paolo Marsili, A. Ortolan, A. Porzio, Matteo Luca Ruggiero, R. Velotta
{"title":"Possible Tests of Fundamental Physics with GINGER","authors":"G. Di Somma, C. Altucci, F. Bajardi, Andrea Basti, N. Beverini, Salvatore Capozziello, G. Carelli, Simone Castellano, D. Ciampini, Gaetano De Luca, A. D. Di Virgilio, F. Fuso, Francesco Giovinetti, E. Maccioni, Paolo Marsili, A. Ortolan, A. Porzio, Matteo Luca Ruggiero, R. Velotta","doi":"10.3390/astronomy3010003","DOIUrl":"https://doi.org/10.3390/astronomy3010003","url":null,"abstract":"The GINGER (gyroscopes in general relativity) project foresees the construction of an array of large frame ring laser gyroscopes, rigidly connected to the Earth. Large frame ring laser gyroscopes are high-sensitivity instruments used to measure angular velocity with respect to the local inertial frame. In particular, they can provide sub-daily variations in the Earth rotation rate, a measurement relevant for geodesy and for fundamental physics at the same time. Sensitivity is the key point in determining the relevance of this instrument for fundamental science. The most recent progress in sensitivity evaluation, obtained on a ring laser prototype, indicates that GINGER should reach the level of 1 part in 1011 of the Earth’s rotation rate. The impact on fundamental physics of this kind of apparatus is reviewed.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"7 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140413749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Generating Stellar Spectra Using Neural Networks 利用神经网络生成恒星光谱
Astronomy Pub Date : 2024-01-24 DOI: 10.3390/astronomy3010001
Marwan Gebran
{"title":"Generating Stellar Spectra Using Neural Networks","authors":"Marwan Gebran","doi":"10.3390/astronomy3010001","DOIUrl":"https://doi.org/10.3390/astronomy3010001","url":null,"abstract":"A new generative technique is presented in this paper that uses Deep Learning to reconstruct stellar spectra based on a set of stellar parameters. Two different Neural Networks were trained allowing the generation of new spectra. First, an autoencoder is trained on a set of BAFGK synthetic data calculated using ATLAS9 model atmospheres and SYNSPEC radiative transfer code. These spectra are calculated in the wavelength range of Gaia RVS between 8400 and 8800 Å. Second, we trained a Fully Dense Neural Network to relate the stellar parameters to the Latent Space of the autoencoder. Finally, we linked the Fully Dense Neural Network to the decoder part of the autoencoder and we built a model that uses as input any combination of Teff, logg, vesini, [M/H], and ξt and output a normalized spectrum. The generated spectra are shown to represent all the line profiles and flux values as the ones calculated using the classical radiative transfer code. The accuracy of our technique is tested using a stellar parameter determination procedure and the results show that the generated spectra have the same characteristics as the synthetic ones.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"4 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140497143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Testing Cosmic Acceleration from the Late-Time Universe 从晚期宇宙测试宇宙加速度
Astronomy Pub Date : 2023-12-14 DOI: 10.3390/astronomy2040020
Jose Agustin Lozano Torres
{"title":"Testing Cosmic Acceleration from the Late-Time Universe","authors":"Jose Agustin Lozano Torres","doi":"10.3390/astronomy2040020","DOIUrl":"https://doi.org/10.3390/astronomy2040020","url":null,"abstract":"We investigate the accelerated cosmic expansion in the late universe and derive constraints on the values of the cosmic key parameters according to different cosmologies such as ΛCDM, wCDM, and w0waCDM. We select 24 baryon acoustic oscillation (BAO) uncorrelated measurements from the latest galaxy surveys measurements in the range of redshift z∈[0.106,2.33] combined with the Pantheon SNeIa dataset, the latest 33 H(z) measurements using the cosmic chronometers (CCs) method, and the recent Hubble constant value measurement measured by Riess 2022 (R22) as an additional prior. In the ΛCDM framework, the model fit yields Ωm=0.268±0.037 and ΩΛ=0.726±0.023. Combining BAO with Pantheon plus the cosmic chronometers datasets we obtain H0=69.76±1.71 km s−1 Mpc−1 and the sound horizon result is rd=145.88±3.32 Mpc. For the flat wCDM model, we obtain w=−1.001±0.040. For the dynamical evolution of the dark energy equation of state, w0waCDM cosmology, we obtain wa=−0.848±0.180. We apply the Akaike information criterion approach to compare the three models, and see that all cannot be ruled out from the latest observational measurements.","PeriodicalId":80577,"journal":{"name":"Astronomy","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138973005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
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