Astrophysics and Space Science最新文献

Phenomenological relations linking thermodynamics and kinetic theory in condensed matter have been empirically verified in numerous systems, yet their theoretical derivation from first principles remains an open question. One such relation is the so-called “excess-entropy scaling”. Do N-body gravitational systems exhibit a similar relation? We provide an affirmative response to this question, albeit with some limitations. Our analysis relies on a well-established thermodynamical quasi-equilibrium model for the cosmological N-body problem, along with an appropriate diffusion model for gravitational interactions. By identifying a scaling region, we were able to estimate diffusion coefficients directly from observational two-particle correlation functions or counts-in-cells distributions in large-scale structures. Intriguingly, the phenomenon of excess-entropy scaling manifests primarily during the nonlinear, asymptotic clustering phase preceding a potential thermodynamic phase transition.

The hyperfine transition of atomic hydrogen at a wavelength of about 21 cm is an essential tool for studies of interstellar gas. It has been argued that also fine-structure transitions of hydrogen could be detected in astronomical sources. Our aim is to detect the fine-structure transition (2^{2}P_{3/2}-2^{2}S_{1/2}) of hydrogen at ∼10 GHz in the radio spectrum of the Sun, with a spectral resolution which enables a detailed study of the line profile. The Sun was observed with the 13.7 m radio telescope at the Metsähovi Radio Observatory, in Finland. We detect emission from two of the three hyperfine components of the transition. The width of the components is ∼15 MHz, much less than the expected natural line width of ∼100 MHz (broadened solely by the uncertainty principle). At red-shifted Doppler velocities, the lines show enhanced emission and possibly self-absorption. If the absorption happens at the chromosphere, our observations challenge the traditional view that chromospheric temperature increases gradually towards higher altitudes. Our unconventional results have to be confirmed by further observations. This transition would be the only known spectral line in the Sun at radio frequencies.

We report 11 new radio continuum measurements of established planetary nebulae (PNe) in the Small Magellanic Cloud (SMC) that we observed at 5.5 and 9 GHz with the Australia Telescope Compact Array (ATCA). These new radio detections are PNe with catalogued names: SMP SMC 2, SMP SMC 3, SMP SMC 5, SMP SMC 8, SMP SMC 13, SMP SMC 14, SMP SMC 19, MGPN SMC 8, SMP SMC 22, SMP SMC 26 and SMP SMC 27. We supplement our data with available high-resolution radio observations from MeerKAT and construct the spectral energy distribution (SED) in the radio regime for each PN. We determine the angular diameters of four of the eleven PNe from radio flux density alone using SED modelling, which are compared to the corresponding Hubble Space Telescope (HST) optical diameters. Our results are in good agreement with the optically-derived angular diameters from independent HST observations. We plot our new diameter estimates against a larger sample of Galactic PNe and compare diameters obtained via the SED method to those found in the literature. Our sample diameters, when compared to the Galactic PNe, suggest that the angular diameter measurement methods are comparable independent of the distance.

Astronomical observatories require sites with high altitudes, a high number of clear nights, and minimal light pollution. This study utilizes Geographic Information Systems and Multi-Criteria Decision Analysis to evaluate the suitability of Balkan regions for establishing International Dark Sky Parks (IDSP) based on the criteria set by the International Dark Sky Association. Three scenarios (DSPI A, B and C) were formulated to assess suitability under different conditions using satellite data on light pollution, cloud cover, elevation and water bodies. Although no ‘Conservation Area’ or ‘International Dark Sky Park’ sites were found due to the prevalence of light pollution, promising ‘reserve areas’ and astronomical observatory sites were identified, mainly concentrated in the southern Balkans inside the Montenegro-Bulgaria-Greece triangle. The southern part of Macedonia has twice as many clear nights (an average of approximately 240 nights) compared to the north. The southern region of Macedonia exhibited a range of brightness levels, while the Rozhen National Astronomical Observatory in Bulgaria had the darkest recorded sky brightness (20.89 (mathrm{mag}_{textrm{SQM}}) arcsec⁻²) and the highest suitability score (0.69). The Peloponnese offers suitable locations for astronomical sites in all scenarios. Higher altitudes and lower latitudes have more favorable conditions. The Balkans contain a significant proportion of reserve areas (24.8% of the region), with Bulgaria having the largest share, despite the lack of ideal astronomical sites. It is important to note that long-term in-situ observations should be carried out after the site selection process has been completed.

Morphological evolution of expanding shells of fast-mode magnetohydrodynamic (MHD) waves through an inhomogeneous ISM is investigated in order to qualitatively understand the complicated morphology of shell-type supernova remnants (SNR). Interstellar clouds with high Alfvén velocity act as concave lenses to diverge the MHD waves, while those with slow Alfvén velocity act as convex lenses to converge the waves to the focal points. By combination of various types of clouds and fluctuations with different Alfvén velocities, sizes, or wavelengths, the MHD-wave shells attain various morphological structures, exhibiting filaments, arcs, loops, holes, and focal strings, mimicking old and deformed SNRs.

Stellar activity cycles on magnetically active stars can be estimated by molecular absorption bands. We have previously introduced a molecular index which compares absorptional line strength of the (TiOlambda 567nm) with its nearby continuum has previously been introduced. In this work we use this indicator to evaluation long-term activity variations for Proxima Centauri star, using spectroscopic data from HARPS. The results indicate periodicity with an activity period of (2873_{-53.9}^{+47.4}) days, which is similar to the previous measurements from other indicators.

Neutron stars (NSs) are observed with high space velocities and elliptical orbits in binaries. The magnitude of these effects points to natal kicks that originate from asymmetries during the supernova (SN) explosions. Using a growing set of long-time 3D SN simulations with the Prometheus-Vertex code, we explore the interplay of NS kicks that are induced by asymmetric neutrino emission and by asymmetric mass ejection. Anisotropic neutrino emission can arise from a large-amplitude dipolar convection asymmetry inside the proto-NS (PNS) termed LESA (Lepton-number Emission Self-sustained Asymmetry) and from aspherical accretion downflows around the PNS, which can lead to anisotropic neutrino emission (absorption/scattering) with a neutrino-induced NS kick roughly opposite to (aligned with) the kick by asymmetric mass ejection. In massive progenitors, hydrodynamic kicks can reach up to more than 1300 km s⁻¹, whereas our calculated neutrino kicks reach (55–140) km s⁻¹ (estimated upper bounds of (170–265) km s⁻¹) and only ∼(10–50) km s⁻¹, if LESA is the main cause of asymmetric neutrino emission. Therefore, hydrodynamic NS kicks dominate in explosions of high-mass progenitors, whereas LESA-induced neutrino kicks dominate for NSs born in low-energy SNe of the lowest-mass progenitors, when these explode nearly spherically. Our models suggest that the Crab pulsar with its velocity of ∼160 km s⁻¹, if born in the low-energy explosion of a low-mass, single-star progenitor, should have received a hydrodynamic kick in a considerably asymmetric explosion. Black holes, if formed by the collapse of short-lived PNSs and solely kicked by anisotropic neutrino emission, obtain velocities of only some km s⁻¹.

In this paper, we performed solar synodic period (∼27 days) and heliospheric effect for selected solar activity parameters: sunspot number (SSN), sunspot area (SSA), modified coronal index (MCI), solar radio flux (F10.7), chromospheric composite Mg II index and Galactic cosmic rays (GCRs), during the ascending phase of solar cycles 24 and 25 (2009–2012 and 2020 to 2023). The Wavelet analyses of daily data of SSN, SSA, MCI, Mg II, and F10.7, reveal a solar rotational period of ∼27 days. The R Robper method is used to validate the observed periods; near one solar rotational period during the ascending phase of solar cycles 24 and 25. We observed cross-correlation and time lag for solar activity parameters (SSN, SSA, MCI, Mg II, and F10.7) with GCRs during the ascending phase of solar cycles 24 and 25 (2009–2012 and 2020 to 2023). We found the highest time lag for SSA is ∼300 days, and for SSN is ∼270 days during the ascending phase of solar cycle 25. We also found the highest cross-correlation values are 0.998 and 0.996 for chromospheric composite Mg II index with Galactic cosmic rays (GCRs) during the ascending phase of solar cycle 24 and 25 respectively. We found the chromospheric composite Mg II index is a good indicator of solar activity indices and it is strongly correlated to SSN.