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Astronomy, Volume 2, Issue 3 (September 2023) – 6 articles

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20 pages, 711 KiB  
Article
Emergent Strings at an Infinite Distance with Broken Supersymmetry
Astronomy 2023, 2(3), 206-225; https://doi.org/10.3390/astronomy2030015 - 14 Sep 2023
Cited by 1 | Viewed by 596
Abstract
We investigate the infinite-distance properties of families of unstable flux vacua in string theory with broken supersymmetry. To this end, we employ a generalized notion of distance in the moduli space and we build a holographic description for the non-perturbative regime of the [...] Read more.
We investigate the infinite-distance properties of families of unstable flux vacua in string theory with broken supersymmetry. To this end, we employ a generalized notion of distance in the moduli space and we build a holographic description for the non-perturbative regime of the tunneling cascade in terms of a renormalization group flow. In one limit, we recover an exponentially-light tower of Kaluza-Klein states, while in the opposite limit, we find a tower of higher-spin excitations of D1-branes, realizing the emergent string proposal. In particular, the holographic description includes a free sector, whose emergent superconformal symmetry resonates with supersymmetric stability, the CFT distance conjecture and S-duality. We compute the anomalous dimensions of scalar vertex operators and single-trace higher-spin currents, finding an exponential suppression with the distance which is not generic from the renormalization group perspective, but appears specific to our settings. Full article
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13 pages, 976 KiB  
Article
New Strong Constraints on the Central Behaviour of Spherical Galactic Models
Astronomy 2023, 2(3), 193-205; https://doi.org/10.3390/astronomy2030014 - 01 Sep 2023
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Abstract
First of all, we show that any spherically symmetric galactic model with integrated mass profile M(r)0 as r0 is physically correct close to the centre only provided that the circular velocity [...] Read more.
First of all, we show that any spherically symmetric galactic model with integrated mass profile M(r)0 as r0 is physically correct close to the centre only provided that the circular velocity vc(r)0 and the gravitational field g(r)0 as r0. Next, we apply this statement to a broad class of five-parameter spherical galactic models, including most of those used in astrophysics and cosmology. Specifically, we show that the Jaffe and Hernquist models can be trusted only for r0.2Re (Re being the effective radius), while the Navarro–Frank–White (NFW) model cannot describe galaxies in the central region of regular clusters. We also briefly discuss the relevance of our result for the NFW profile of pure dark matter halos. However, we are unable to tell at which central distance the NFW model breaks down in either case, and this is a challenge for future investigations. Full article
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13 pages, 2902 KiB  
Review
Quantum Astronomy at the University and INAF Astronomical Observatory of Padova, Italy
Astronomy 2023, 2(3), 180-192; https://doi.org/10.3390/astronomy2030013 - 23 Aug 2023
Viewed by 1048
Abstract
Twenty years ago, we started to apply quantum optics to the astronomical research carried out inside the Department of Physics and Astronomy and the INAF Astronomical Observatory in Padova, Italy. The initial activities were stimulated by the project of the European Southern Observatory [...] Read more.
Twenty years ago, we started to apply quantum optics to the astronomical research carried out inside the Department of Physics and Astronomy and the INAF Astronomical Observatory in Padova, Italy. The initial activities were stimulated by the project of the European Southern Observatory (ESO) to build a 100 m diameter telescope, the Overwhelmingly Large (OWL) telescope. The enormous photon flux expected from such an aperture suggested that quantum optics concepts be utilized in order to obtain novel astrophysical results. Following initial successful attempts to utilize the orbital angular momentum of the light beam to enhance the visibility of faint companions to bright stars, the Padova team concentrated its efforts on very high time resolution, in order to measure and store the arrival time of celestial photons to better than one nanosecond. To obtain observational results, we built two photon counting photometers (AquEye and IquEye) to be used with our telescopes of the Asiago Observatory and with 4 m class telescopes such as the ESO New Technology Telescope (NTT) in Chile. This paper firstly describes these two instruments and then expounds the results obtained on pulsar light curves, lunar occultations and the first photon counting intensity interferometry measurements of the bright star Vega. Indeed, the correlation of photon arrival times on two or more apertures can lead to extremely high angular resolutions, as shown around 1970 by Hanbury Brown and Twiss. Prospects for quantum intensity interferometry with arrays of Cherenkov light telescopes will also be described. Full article
(This article belongs to the Special Issue Quantum Astronomy)
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15 pages, 545 KiB  
Article
Space Weather Effects on Satellites
Astronomy 2023, 2(3), 165-179; https://doi.org/10.3390/astronomy2030012 - 22 Aug 2023
Cited by 2 | Viewed by 2761
Abstract
The study presents a concise overview on the main effects on satellites due to space weather drivers compared to the well-known interplanetary, magnetospheric and ground-based consequences. The solar-activity-driven influences include specific physics-based effects on the spacecraft surface and on-board electronics due to electromagnetic [...] Read more.
The study presents a concise overview on the main effects on satellites due to space weather drivers compared to the well-known interplanetary, magnetospheric and ground-based consequences. The solar-activity-driven influences include specific physics-based effects on the spacecraft surface and on-board electronics due to electromagnetic emission and energetic particles as well as complex effects due to geomagnetic storms which may endanger the mission performance and spacecraft longevity. We select as test examples the Starlink satellites in the period 2019–2022 and present the temporal correspondence between their launches and the space weather phenomena. Based on comparative analysis, we discuss whether the occurrence vs. the intensity of solar and interplanetary drivers of space weather can be considered as a cause for orbital stability problems and satellite loss. The results suggest that a sequence of geomagnetic disturbances together with multiple weak space weather events could lead to severe levels of atmospheric drag ending in a service or satellite loss. Full article
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12 pages, 2986 KiB  
Article
Simulation of Dynamic Evolution of Ring Current Ion Flux by a Lunar Base Energetic Neutral Atom (ENA) Imaging
Astronomy 2023, 2(3), 153-164; https://doi.org/10.3390/astronomy2030011 - 22 Aug 2023
Cited by 1 | Viewed by 534
Abstract
The distribution of energetic ion flux in the ring current region, such as a meteorological cumulonimbus cloud, stores up the particle energy for a geomagnetic substorm. It is helpful to study the geomagnetic substorm mechanism by using a lunar base ENA imaging simulation [...] Read more.
The distribution of energetic ion flux in the ring current region, such as a meteorological cumulonimbus cloud, stores up the particle energy for a geomagnetic substorm. It is helpful to study the geomagnetic substorm mechanism by using a lunar base ENA imaging simulation of the dynamic evolution of the ring current, and establishing the corresponding relationship between key node events of the substorm. Based on the previous observation experience and our simulation results of the dynamic evolution of the ring current, we propose a macroscopic model of substorms related to the dynamic evolution of ring currents and present the possibility of confirming the causal sequence of some of those critical node events of substorms with the lunar base ENA imaging measurement. IBEX, operating in the ecliptic plane, may even give examples of the telemetry of ring current ion fluxes through ENA measurements during substorms/quiets. Full article
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12 pages, 2389 KiB  
Communication
Spins of Supermassive Black Holes M87* and SgrA* Revealed from the Size of Dark Spots in Event Horizon Telescope Images
Astronomy 2023, 2(3), 141-152; https://doi.org/10.3390/astronomy2030010 - 19 Jul 2023
Cited by 1 | Viewed by 908
Abstract
We reconstructed dark spots in the images of supermassive black holes SgrA* and M87* provided by the Event Horizon Telescope (EHT) collaboration by using the geometrically thin accretion disk model. In this model, the black hole is highlighted by the hot accretion matter [...] Read more.
We reconstructed dark spots in the images of supermassive black holes SgrA* and M87* provided by the Event Horizon Telescope (EHT) collaboration by using the geometrically thin accretion disk model. In this model, the black hole is highlighted by the hot accretion matter up to the very vicinity of the black hole event horizon. The existence of hot accretion matter in the vicinity of black hole event horizons is predicted by the Blandford–Znajek mechanism, which is confirmed by recent general relativistic MHD simulations in supercomputers. A dark spot in the black hole image in the described model is a gravitationally lensed image of an event horizon globe. The lensed images of event horizons are always projected at the celestial sphere inside the awaited positions of the classical black hole shadows, which are invisible in both cases of M87* and SgrA*. We used the sizes of dark spots in the images of SgrA* and M87* for inferring their spins, 0.65<a<0.9 and a>0.75, accordingly. Full article
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