Astronomy 

Abstract: A simple phenomenological fit for the power spectrum of scalar (curvature) perturbations during inflation is proposed to analytically describe slow roll of inflaton and formation of primordial black holes (PBH) in the early universe, in the framework of single-field models. The fit is given by a sum of the power spectrum of slow-roll inflation, needed for a viable description of the cosmic microwave background (CMB) radiation in agreement with Planck/BICEP/Keck measurements, and the log-normal (Gaussian) fit for the power spectrum enhancement (peak) needed for efficient PBH production, in the leading (model-independent) approximation. The T-type α-attractor models are used to get the simple CMB power spectrum depending upon the e-folds as the running variable. The location and height of the peak are chosen to yield the PBH masses in the asteroid-size window allowed for the whole (current) dark matter. We find the restrictions on the peak width.

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 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.

Abstract: We elucidate the physical origin of the dark spot in the image of supermassive black hole SgrA* presented very recently by the EHT collaboration. It is argued that this dark spot, which is noticeably smaller than the classical black hole shadow, is the northern hemisphere of the event horizon globe. The classical black hole shadow is unseen in the image of SgrA*. The dark spot in the image of SgrA* is projected within the position of the classical black hole shadow on the celestial sphere. The outer boundary of this dark spot is an equator on the event horizon globe.

Abstract: We parameterize the core of compact spherical star configurations by a mass (mx) and a radius (rx) and study the resulting admissible areas in the total-mass–total-radius plane. The employed fiducial equation-of-state models of the corona at radii r>rx and pressures p≤px with p(r=rx)=px are that of constant sound velocity and a proxy of DYΔ DD-ME2 provided by Buchdahl’s exactly solvable ansatz. The core (r