Polymer science

AS 314 (V452 Sct) is a poorly studied early-type emission-line star, which exhibits an infrared excess at wavelengths longer than 10 μm. Its earlier studies have been limited to small amounts of observational data and led to controversial conclusions about its fundamental parameters and evolutionary status. Comparison of high-resolution spectra of AS 314 taken over 20 years ago with those of Luminous Blue Variables and other high-luminosity objects suggested its observed properties can be explained by a strong stellar wind from a distant (D∼10 kpc) massive star, possibly in a binary system. However, a recent assessment of its low-resolution spectrum along with a new distance from a Gaia parallax (∼1.6 kpc) resulted in an alternative hypothesis that AS 314 is a low-mass post-asymptotic giant branch (post-AGB) star. The latter hypothesis ignored the high-resolution data, which gave rise to the former explanation. We collected over 30 mostly high-resolution spectra taken in 1997–2023, supplemented them with results of long-term photometric surveys, compared the spectra and the spectral energy distribution with those of post-AGB objects and B/A supergiants, and concluded that the observed properties AS 314 are more consistent with those of the latter.

Gamma-Ray Bursts(GRBs) are the most violent and energetic astrophysical phenomena, which I dare call “the Energy Monsters of the Universe”. Indeed, they show an enormous emitted isotropic energy ranging from ∼3 × 1046 erg (GRB 170817A) to ∼1055 erg (GRB 221009A) and a duration ranging from ≈milliseconds to ∼104 s. In this review—which I agreed to write as a scientist not directly involved in the field of GRBs—I will present the history of GRBs from the time of their discovery by chance until the new era whose beginning was marked by the detection of gravitational waves coming from the merger of two neutron stars. I will discuss the experimental results and their physical interpretation, which is still a source of heated debate within the scientific community. Due to the reasonable length of this review and especially given my limited knowledge, I do not claim to have exhausted the complicated topic of GRBs, but to have contributed in making this subject easy to read for non-experts, providing a critical contribution that is hopefully useful to the whole community.

Gamma-ray bursts (GRBs) are among the most luminous electromagnetic transients in the universe, providing unique insights into extreme astrophysical processes and serving as promising probes for cosmology. Unlike Type Ia supernovae, which have a unified explosion mechanism, GRBs cannot directly act as standard candles for tracing cosmic evolution at high redshifts due to significant uncertainties in their underlying physical origins. Empirical correlations derived from statistical analyses involving various GRB parameters provide valuable information regarding their intrinsic properties. In this brief review, we describe various correlations among GRB parameters involving the prompt and afterglow phases, discussing possible theoretical interpretations behind them. The scarcity of low-redshift GRBs poses a major obstacle to the application of GRB empirical correlations in cosmology, referred to as the circularity problem. We present various efforts aiming at calibrating GRBs to address this challenge and leveraging established empirical correlations to constrain cosmological parameters. The pivotal role of GRB sample quality in advancing cosmological research is underscored. Some correlations that could potentially be utilized as redshift indicators are also introduced.

Observations of Very High Energy (VHE) gamma ray sources using the ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs) play a pivotal role in understanding the non-thermal energetic phenomena and acceleration processes under extreme astrophysical conditions. However, detection of the VHE gamma ray signal from the astrophysical sources is very challenging, as these telescopes detect the photons indirectly by measuring the flash of Cherenkov light from the Extensive Air Showers (EAS) initiated by the cosmic gamma rays in the Earth’s atmosphere. This requires fast detection systems, along with advanced data acquisition and analysis techniques to measure the development of extensive air showers and the subsequent segregation of gamma ray events from the huge cosmic ray background, followed by the physics analysis of the signal. Here, we report the development of a python-based package for analyzing the data from the Major Atmospheric Cherenkov Experiment (MACE), which is operational at Hanle in India. The Python-based MACE data Analysis Package (PyMAP) analyzes data by using advanced methods and machine learning algorithms. Data recorded by the MACE telescope are passed through different utilities developed in the PyMAP to extract the gamma ray signal from a given source direction. We also propose a new image cleaning method called DIOS (Denoising Image of Shower) and compare its performance with the standard image cleaning method. The working performance of DIOS indicates an advantage over the standard method with an improvement of ≈25% in the sensitivity of MACE.

We obtain universal relations for fluid spheres without rotation made of dark energy assuming the extended Chaplygin gas equation-of-state. After integrating the relevant differential equations, we make a fit to obtain the unknown coefficients of the functions (a) normalized moment of inertia versus dimensionless deformability and (b) normalized moment of inertia versus factor of compactness. We find that the form of the functions does not depend on the details of the underlying equation-of-state.

Cooling down large test masses up to 200 kg, as foreseen for the Einstein Telescope, is a complex challenge combining cutting-edge technological achievements from different disciplines with the experience gained from both room-temperature and cryogenic-temperature detector development communities. We set up an apparatus designed to test cryogenic mechanical suspensions for the payload system. They should have high quality factors and enable sufficient heat extraction greater than 0.3 W. The facility is on a university campus where cryofluid servicing is not feasible. As a result, a system that incorporates conductive cooling technology was developed. The project has two main goals: validating crystalline suspensions in a realistic Einstein Telescope cryogenic payload and testing new solutions for radiative thermal shielding. No particular measures are planned for the vibration isolation system.

Quantum technology is central to the operation of modern gravitational-wave detectors and will play crucial role in the success of next-generation observatories, such as the Einstein Telescope. There, quantum squeezed light will be utilized to suppress quantum noise across the entire detection band, a task that demands advancements in several areas of quantum technology. This review provides an introduction to the quantum technologies employed in gravitational-wave detection and explores in detail their properties, challenges, and the potential they hold for the Einstein Telescope.

The aim of the analysis of data from the Gaia Space Observatory is to obtain kinematic parameters of the collective motion of stars in a part of our galaxy. This research is based on a statistical analysis of the motion of 55,038,539 stars selected in different directions from the Sun up to a distance of 3–6 kpc. We developed statistical methods for the analysis working with input data represented by the full astrometric solution (five parameters). Using the proposed statistical methods, we obtained the local velocity of the Sun U⊙,V⊙,W⊙=(9.58,16.25,7.33)±(0.05,0.04,0.02)stat±(0.7,0.9,0.1)syst km/s and the rotation velocity of the galaxy at different radii. For the Sun’s orbit radius, we obtained the velocity of the galaxy rotationVc≈234±4 km/s. Collective rotation slows down in the region under study linearly with distance from the disk plane: ΔV/ΔZ≅33.5kms−1kpc−1. We showed that the different kinematic characteristics and distributions, which depend on the position in the galaxy, can be well described in the studied 3D region by a simple Monte Carlo simulation model, representing an axisymmetric approximation of the galaxy kinematics. The optimal values of the six free parameters were tuned by comparison with the data.

The Einstein Telescope (ET) will be a third-generation Gravitational Wave (GW) detector that will tackle cutting-edge technological challenges. The ET will be constructed at a depth of 200–300 m to isolate it from vibrations caused by seismic waves and human activities, which are sources of noise for GW detection. To meet the ET’s objectives, it will be necessary to improve low-frequency sensitivity by about two orders of magnitude compared to current interferometers (LIGO, Virgo). Magnetic noise is a limiting noise in the frequency range from a few Hz up to around 100 Hz in future GW detectors. This article will discuss the magnetic noise mitigation strategies under development, based on experiences from Virgo.

The star γ Cas and its analogs are a subset of Be stars that display particularly hard and bright thermal X-ray emission, which has no equivalent among other massive stars. Here, I will review their characteristics and present the latest results of our optical and X-ray monitoring campaigns, including an assessment of the links between the circumstellar environment and the high-energy properties. Possible scenarios to explain this phenomenon will be presented in light of these observational results.

Gamma-ray bursts are known to display various features on top of their canonical behavior. In this short review, we will describe and discuss two of them: the ultra-long gamma-ray bursts, which are defined by an extreme duration of their prompt phase, and the plateau phase, which is defined by a steady phase of large duration at the start of the afterglow. We will review the main properties of those two phenomena, and will discuss their possible origin, in light of the standard fireball model of gamma-ray bursts. A final section will discuss the future missions, which could bring new evidence to the study of those objects.

It has long been known that the observed mass surface density of cored dark matter (DM) halos is approximately constant, independently of the galaxy mass (i.e., ρcrc≃constant, with ρc and rc being the central volume density and the radius of the core, respectively). Here, we review the evidence supporting this empirical fact as well as its theoretical interpretation. It seems to be an emergent law resulting from the concentration–halo mass relation predicted by the current cosmological model, where the DM is made of collisionless cold DM particles (CDM). We argue that the prediction ρcrc≃constant is not specific to this particular model of DM but holds for any other DM model (e.g., self-interacting) or process (e.g., stellar or AGN feedback) that redistributes the DM within halos conserving its CDM mass. In addition, the fact that ρcrc≃constant is shown to allow the estimate of the core DM mass and baryon fraction from stellar photometry alone is particularly useful when the observationally expensive conventional spectroscopic techniques are unfeasible.

The results of observations of the object Th4-4 in 1970–2024 showed that during this period the object went through several stages, when its characteristics corresponded to different classes of objects: Be star, symbiotic star and planetary nebula. Currently, the object appears to be a low-excitation planetary nebula.

We propose that modifications to the Higgs potential within a narrow atmospheric layer near the event horizon of an astrophysical black hole could significantly enhance the rate of sphaleron transitions, as well as transform the Chern–Simons number into a dynamic variable. As a result, sphaleron transitions in this region occur without suppression, in contrast to low-temperature conditions, and each transition may generate a substantially greater baryon number than would be produced by winding around the Higgs potential in Minkowski spacetime. This effect amplifies baryon number violation near the black hole horizon, potentially leading to a considerable generation of matter. Given the possibility of a departure from equilibrium during the absorption of matter and the formation of relativistic jets in supermassive black holes, we conjecture that this process could contribute to the creation of a significant amount of matter around such black holes. This phenomenon may offer an alternative explanation for the rapid growth of supermassive black holes and their surrounding galaxies in the early Universe, as suggested by recent observations from the James Webb Space Telescope. Furthermore, this mechanism may provide insights into the low-mass gap puzzle, addressing the observed scarcity of black holes with masses near the Oppenheimer–Volkoff limit.

So far, most of the about 5700 exoplanets have been discovered mainly with radial velocity and transit methods. These techniques are sensitive to planets in close orbits, not being able to probearge star–planet separations. μ-lensing is the indirect method that allows us to probe the planetary systems at the snow-line and beyond, but it is not a repeatable observation. On the contrary, direct imaging (DI) allows for the detection and characterization ofow mass companions at wide separation (≤5–6 au). The main challenge of DI is that a typical planet–star contrast ranges from 10−6, for a young Jupiter in emittedight, to 10−9 for Earth in reflectedight. In theast two decades, aot of efforts have been dedicated to combiningarge (D ≥ 5 m) telescopes (to reduce the impact of diffraction) with coronagraphs and high-order adaptive optics (to correct phase errors induced by atmospheric turbulence), with sophisticated image post-processing, to reach such a contrast between the star and the planet in order to detect and characterize cooler and closer companions to nearby stars. Building on the first pioneering instrumentation, the second generation of high-contrast imagers, SPHERE, GPI, and SCExAO, allowed us to probe hundreds of stars (e.g., 500–600 stars using SHINE and GPIES), contributing to a better understanding of the demography and the occurrence of planetary systems. The DI offers a possible clear vision for studying the formation and physical properties of gas giant planets and brown dwarfs, and the future DI (space and ground-based) instruments with deeper detectionimits will enhance this vision. In this paper, we briefly review the methods, the instruments, the main sample of targeted stars, the remarkable results, and the perspective of this rising technique.