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Astronomy, Volume 3, Issue 2 (June 2024) – 3 articles

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8 pages, 588 KiB  
Brief Report
Constraining the Inner Galactic DM Density Profile with H.E.S.S.
by Jaume Zuriaga-Puig
Astronomy 2024, 3(2), 114-121; https://doi.org/10.3390/astronomy3020008 - 11 Apr 2024
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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 [...] Read more.
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 γ1.3. 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 γ0.8, with an internal slope of γsp-stars=1.5. Full article
(This article belongs to the Special Issue Current Trends in Cosmology)
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14 pages, 320 KiB  
Article
Cosmography of the Minimally Extended Varying Speed-of-Light Model
by Seokcheon Lee
Astronomy 2024, 3(2), 100-113; https://doi.org/10.3390/astronomy3020007 - 07 Apr 2024
Cited by 1 | Viewed by 332
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. [...] Read more.
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. Full article
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33 pages, 7491 KiB  
Review
Refracted Gravity Solutions from Small to Large Scales
by Valentina Cesare
Astronomy 2024, 3(2), 68-99; https://doi.org/10.3390/astronomy3020006 - 05 Apr 2024
Viewed by 451
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Current Trends in Cosmology)
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