Search Results (95)

We present new results of the investigation of the optical spectrum features of the central star with the B[e] phenomenon in the system of the IR-source IRAS 01005+7910 using high-resolution ($R\ge$ 60,000) spectroscopy data taken by the 6 m BTA telescope with the NES spectrograph. Comparison of the spectra obtained at different times shows significant variations in the complex H$\alpha$ and H$\beta$ line profiles, such as a systematic increase in their emission peak strengths in 2025–2026 compared to those observed in 2013 as well as a strong variability in their wind component. A detected variable radial velocity $V_{\odot }$ from $-20$ to $-68$ km s⁻¹ with a standard deviation of the mean value of K = 8.0 km s⁻¹ can be interpreted as a result of pulsations or the presence of a companion. The stationary positions of forbidden lines with a mean radial velocity of $V_{\odot }=-51.38\pm 0.26$ km s⁻¹ are taken as an improved systemic velocity. Overall, a set of properties of IRAS 01005+7910 points to its status as a post-AGB star, which has undergone the hot-bottom burning phase. Full article

The blazar PKS 0346-27 at redshift $z=0.991$ is among the most distant extragalactic sources detected in very high energy $\gamma$-rays. It underwent a major flare reaching TeV energies in November 2021. Recent modelling of its spectral energy distribution favoured a single-zone proton–synchrotron-dominated hadronic model with bulk Lorentz factor $\Gamma =10$ over a single-zone leptonic jet model with much higher $\Gamma$. Here we analyse archival radio data to give independent estimates of the jet bulk Lorentz factor. We present high-resolution radio imaging and brightness distribution modelling, as well as flare detection in long-term radio flux density monitoring data, and obtain $\Gamma \lesssim 10$ values. This lends support to the hadronic model proposed for the PKS 0346-27 jet. Our results highlight the importance of long-term, very long baseline interferometry and total flux density monitoring in studying blazar jets. Full article

The passage from generic (non-interacting) plasma to cold plasma with dust around a spherically symmetric black hole is newly analytically studied. The configurations are newly written, and the behaviours of the observer are this way spelt out. The conservation of mass flux and that of the energy flux are used. The velocities of the observer are newly classified in the case of (non-interacting) hot plasma with dust for the transition to a configuration of (non-interacting) cold plasma with dust. The suitable functional dependence of the radial component of the velocity of the observer is now expressed in order to select the configurations which allow for the transition. The passage to a configuration of (non-interacting) cold plasma with dust is proved to be defined after the suitable integration conditions of the mass flux and of the energy flux, plus the suitable functional dependence of the radial component of the velocity of the observer are found. The spherical accretion is newly written. The emissions of the new accretion mechanism are due to (1) the variation in the gravitational potential as from blue further studies of the Author; (2) the radiation due to the change in the gravitational potential as described in the Landau–Lifshitz–Pitaevskii equations; (3) the standard electrodynamics radiation; and (4) the radiation of the positron (quantum mechanism) from the electron–positron pair of the emitted photon (in the Landau–Lifshitz–Lindhard scheme). Full article

The transits of Venus occur in couples every 105/122 years: the observed ones were in 1639; 1761–1769; 1874–1882; and 2004–2012. The next couple will occur in the years 2117 and 2125. We need all four contacts to determine the solar diameter accurately. The black-drop phenomenon blurs internal contacts, so we developed a parabolic analysis of the chords drawn by the disk of Venus on the solar limb. The extrapolation of the zeroes gives the contact timings. We tested this method with some high-quality images obtained in 2004 and 2012, and we applied it to the observations of 2012 in a visual band (Huairou Solar Observing Station, hazy weather) and H-alpha (Shen Zen Astronomical Observatory). To exclude a reduction in the measured diameter by the haze, we made two series of measures at the Clementine Gnomon (Rome) and at the PHYSIS telescope (Rome), under various sky transparencies and with diffraction-limited instruments. The haze and the low altitudes above the horizon reduced accuracy at all first contacts examined, without changing the solar diameter. Our measures obtained in China during the transit of 2012 yielded a photospheric radius R_⊙P = 959.33″ ± 0.06″, based on 76 + 75 diffraction-limited images; this is compatible with the chromospheric radius measured at the base of the spiculae, which is R_⊙C = 959.78″ ± 0.11″, relying on 7 + 5 diffraction-limited series of images. Full article

We formulate within Supergravity a model of induced-gravity inflation, excellently consistent with ACT DR6, inspired by the Palatini gravity. The inflaton belongs in the decomposition of a conjugate pair of Higgs superfields which lead to the spontaneous breaking of a $U{\left(1\right)}_{B-L}$ symmetry at a scale close to the range (0.145–8.35) × 10¹⁶ GeV. The inflaton field is canonically normalized thanks to one real and shift-symmetric contribution into the Kähler potential. It also includes two separate holomorphic and antiholomorphic logarithmic terms, the argument of which can be interpreted as the coupling of the inflaton to the Ricci scalar. The attainment of inflation allows for subplanckian inflaton values and energy scales below the cut-off scale of the corresponding effective theory. Embedding the model in a $B-L$ extension of the MSSM we show how the $\mu$ parameter can be generated and non-thermal leptogenesis can be successfully realized. An outcome of our scheme is split SUSY with gravitino mass in the range (40–60) $\mathrm{PeV}$, which is consistent with the results of LHC on the Higgs boson mass. Full article

In this review, the formation of the Oort Cloud is illuminated from several aspects. One is the history of the subject with an outline of the fundamental discoveries by Öpik, Oort and Hills. It is argued that the basic reason for judging Oort as the real discoverer is that he had access to observational data in the form of original orbits of long period comets. Further landmarks are identified, like the exploration of the role of the Galactic tide in the supply of observable comets by Heisler and Tremaine, the clarification of a synergy between tide and stars as the reason for a continued, efficient supply by Rickman et al., the discovery by Kaib and Quinn that inner core comets become observable due to planetary perturbations, disguised as new comets, and the demonstration of how Oort Cloud formation may work in the realm of the Nice Model by Brasser and Morbidelli. Further discussions refer to the possible role of the Grand Tack model in Oort Cloud formation and recent developments like Pan-STARRS in obtaining better data on very distant comets and Gaia in identifying stellar encounters in the close past and future with ensuing, important modifications of the Oort Cloud. It is finally argued that an important Galactic sculpting has occurred since the primordial Oort Cloud was formed by means of global shake-up events resulting from impulses imparted to the Sun by external perturbers like massive stars or Giant Molecular Clouds, and that this may be the real reason for the survival of an outer halo that reveals the existence of the Oort Cloud through the Oort spike. Full article

The jet structure plays an important role in both the prompt and afterglow emission phases of gamma-ray bursts (GRBs). Whether GRB jets are better described by uniform (top-hat) or structured models remains an open question. We use the afterglowpy Python package to numerically model the late X-ray afterglow light curves of a large sample of long and short GRBs, and apply the Bayesian Information Criterion (BIC) to compare the performance of top-hat and Gaussian structured jet models. Within our adopted modeling framework, we find that the top-hat model is preferred by the BIC for ∼78.9% (150/190) of long GRBs and 70% (7/10) of short GRBs. GRB 180205A and GRB 140515A exhibit $\Delta$BIC < 2 for all three model comparisons, indicating that top-hat, Gaussian, and power-law jets provide equivalent fits to their afterglow light curves. This large-sample analysis suggests that uniform jets may be more common than structured jets in the observed GRB population, although this conclusion is subject to the limitations of our model assumptions and the BIC-based model selection criterion. Furthermore, we find that the best-fit distributions of observer angle ${\theta }_{\mathrm{obs}}$, electron energy fraction ${ϵ}_e$, and isotropic equivalent energy $E_0$ differ significantly between the top-hat and Gaussian jet models, with ${\theta }_{\mathrm{obs}}$ showing the most pronounced distinction. Full article

We report six radio observations of four microquasars—SS 433, GRS 1915+105, Cyg X-3 and MAXI J1820+070—conducted between 2022 and 2025 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) using its pulsar backend, achieving a time resolution of 98.304 $\mathsf{\mu }$s across an effective feed range of 1.04–1.45 GHz. A major focus of this work is the development of a standardized calibration pipeline for microquasar observations, including RFI mitigation, flux density, and polarization calibration, as well as multi-beam correlation inspections. Using On–Off mode and cross-beam verification, radio activity was detected in SS 433, GRS 1915+105 and Cyg X-3, while MAXI J1820+070 remained inactive. Both SS 433 and GRS 1915+105 show low linear polarization degrees of only a few percent. No credible quasi-periodic oscillations (QPOs) were detected in the 0.01–100 Hz range, suggesting that radio QPOs within this frequency range are relatively rare compared to those observed in the X-ray band. We therefore highlight the importance of future monitoring with high–time-resolution and high–sensitivity radio telescopes such as FAST, which will be crucial for revealing the correlation between jet and accretion processes and for uncovering the physical origin of QPOs. Full article

We investigate the cosmological implications of torsion–boundary gravity with explicit matter coupling in f(T,B,𝓣) gravity. The purpose is to examine if such couplings offer observationally viable extensions to standard cosmology. Focusing on linear and power-law model realizations, we derive the modified Friedmann equations and analyze the resulting background dynamics. Using a combination of late-time datasets—including Cosmic Chronometers, Type Ia Supernovae, and Baryon Acoustic Oscillations—we perform a joint likelihood analysis to constrain the model parameters. Our results show that both f(T,B,𝓣) models remain compatible with current observations and effectively reduce to the ΛCDM paradigm in their appropriate parameter limits. While the power-law model exhibits mild dynamical deviations at intermediate redshifts, it remains statistically indistinguishable from the standard cosmological model. We conclude that f(T,B,𝓣) gravity represents a viable and robust extension of torsional modified gravity, motivating further study of non-minimal matter–geometry couplings in cosmology. Full article

If our observable Universe is only a tiny region of a vastly larger and conformally older spacetime, then the usual formulations of the classical flatness and horizon problems of the Hot Big Bang can be reinterpreted as artifacts manifesting an observational selection effect; we occupy a small causal domain of a much larger causally-connected and possibly non-flat spacetime. A sufficiently large positive cosmological constant, $\Lambda$, sets the future asymptotic horizon scale of the observable Universe, ∼${\Lambda }^{-1/2}$, thereby implying that the observable Universe may simply be a minute patch of a far larger pre-existing one, hereafter a Small Patch Hypothesis. Importantly, this observational bound is purely geometric; regardless of when the Universe is observed, the maximum accessible scale is finite and fixed by $\Lambda$, independent of inflationary dynamics, anthropic arguments, or assumptions about the global hosting spacetime. The externally possibly frozen past-eternal state implied by a pre-existing, causally connected spacetime motivates, but does not strictly require, viewing the perturbation field as being in (or arbitrarily close to) a coarse-grained maximum-entropy—equilibrium—configuration. Conditionalizing only on fixed mean and variance, a Gaussian distribution uniquely emerges, while the absence of entropy gradients corresponds to adiabaticity. In this work these features are therefore treated as plausible maximum-ignorance priors for super-horizon perturbations, rather than as rigorously derived consequences of a fully developed microscopic notion of gravitational entropy. In this sense, inflation becomes one viable realization of the proposed Small Patch Hypothesis. Here, one particular non-inflationary alternative is considered for illustrative purposes in which a primordial spectrum $P_{\zeta }\left(k\right)$ of the gauge-invariant perturbation $\zeta$ that pre-dates the Big Bang grows logarithmically toward large scales, $k\to 0$, and in fact diverges at some finite $k_c$. If $k_c\ll {\Lambda }^{-1/2}$, then our local cosmic patch probes only the regime where $\zeta \ll 1$ and appears exceptionally smooth. Over the comparatively narrow observable window, this $P_{\zeta }\left(k\right)$ mimics a slightly red-tilted, inflation-like spectrum. Rather than introducing high-energy new fields, this perspective frames large-scale homogeneity, isotropy, Gaussianity, adiabaticity, and the observed thermodynamic Arrow of Time as possible consequences of restricted observational access to a much larger Universe in equilibrium, rather than signatures of a unique early-Universe mechanism. Current observations cannot distinguish this logarithmically running spectrum from the standard power-law one, but future probes—for example high-resolution 21-cm measurements of the Dark Ages—may be able to falsify it. Full article

A large number of transits have been observed by TESS from the rapidly orbiting exoplanet 55 Cancri e. This amount of transit data, combined with the relatively high frequency of TESS observations, allows for a direct measurement of not only the planetary radius and orbital parameters but also the limb darkening coefficients of the host star. We obtain a planetary radius of $1.64\pm 0.10$ earth radii, an orbital radius of $0.019\pm 0.009$ AU, and an orbital inclination of $85\pm 17$ degrees. For the quadratic limb darkening coefficients $u_1$ and $u_2$ we report measurements of $u_1=0.58\pm 0.48$ and $u_2=0.64\pm 0.55$, and discuss strategies to reduce the uncertainty in the measurement. We also measured the curvature of the transit depth as a function of time using an effective parametrization $I^{\prime }\left(t\right)=C\left(t^2\right)$, and found $C=0.28\pm 0.03$ in units of relative intensity per day squared. This parametrization resulted in a higher goodness-of-fit value than the quadratic model, with a reduced ${\chi }^2$ of 1.153 rather than 1.201 for the quadratic model, and a $\mathrm{\Delta }BIC$ of 31.75 in favor of the effective parametrization. Full article

The dynamics of two point masses interacting in a gravitational field has been the object of several scientific works. However, the complete explicit solution of the two-body problem is, to the best of our knowledge, not always available in the scientific literature. In this work, we describe the dynamics of a two-body system with that of an equivalent single-body with a reduced mass. Then, we solve the specific problems for elliptical, circular and parabolic trajectories, starting from different initial conditions. Through detailed analytical calculations, we write the Cartesian equations of the trajectories and the equations of motion both in the reference system of the centre of mass and in the original reference system. The proposed methodology is a simple but rigorous way to analyse the two-body dynamics under gravitational interactions, and can be applied also to more complex cases, such as the motion in a perturbed Newtonian potential and/or precession problems. The treatment presented in this work is particularly suitable to undergraduate students. Full article

Forty-two Jupiter Mass Binary Objects (JuMBOs) have been discovered in the Trapezium Cluster: either brown dwarf stars or planets mutually orbiting in pairs. Here it is shown that, just as in galaxies and wide binaries, the mutual orbits of the objects in each of these twin systems deviate from the Newtonian and level off around a mutual acceleration of $2c^2/\Theta =2\times {10}^{-10}$ m/s² supporting the minimum acceleration predicted by Quantised Inertia (QI), a theory that attributes inertial mass to an interaction between information horizons and quantum fields and predicts galaxy rotation without the need for dark matter. QI further predicts that the JuMBOs with separations of 400 AU should show orbital anomalies of 70 m/s. This could be tested using spectral Doppler data. Full article

IC 10 is a dwarf galaxy in Cassiopeia, located at a distance of 660 kpc, and hosts a young stellar population, a large number of Wolf–Rayet stars, and a large number of massive stars in general. Utilizing a series of 11 Chandra observations (spanning 2003–2021, with a total exposure of 235.1 ks), 375 point sources of X-ray emission were detected. Similar studies have been conducted earlier in the central region of IC 10. Here, we consider all regions covered by Chandra-ACIS. By comparing our catalog of X-ray sources with a published optical catalog, we found that 146 sources have optical counterparts. We also created a list of 60 blue supergiant (SG) candidates with X-ray binary (XRB) companions by using an optical color–magnitude selection criterion to isolate the blue SGs. Blue SG-XRBs form a major class of progenitors of double-degenerate binaries. Hence, their numbers are an important factor in modeling the rate of gravitational-wave sources. Identifying the nature of individual sources is necessary as it paves the way toward a comprehensive census of XRBs in IC 10, thus enabling meaningful comparisons with other Local Group galaxies exhibiting starbursts, such as the Magellanic Clouds. Full article

Cosmological scenarios wherein the cumulative number of spontaneously formed, cognitively impaired, disembodied transient observers is vastly larger than the corresponding number of atypical ‘ordinary observers’ (OOs) formed in the conventional way—essentially via cosmic evolution and gravitational instability—are disqualified in modern cosmology on the grounds of Cognitive Instability—the untrustworsiness of one own’s reasoning—let alone the atypicality of OOs like us. According to the concordance ΛCDM cosmological model—when described in the (expanding) ‘cosmic frame’—the cosmological expansion is future-eternal. In this frame we are atypical OOs, which are vastly outnumbered by typical Boltzmann Brains (BBs) that spontaneously form via sheer thermal fluctuations in the future-eternal asymptotic de Sitter spacetime. In the case that dark energy (DE) ultimately decays, the cumulative number of transient ‘Freak Observers’ (FOs) formed and destroyed spontaneously by virtue of the quantum uncertainty principle ultimately overwhelms that of OOs. Either possibility is unacceptable. We argue that these unsettling conclusions are artifacts of employing the (default) cosmic frame description in which space expands. When analyzed in the comoving frame, OOs overwhelmingly outnumber both BBs and FOs. This suggests that the dual comoving description is the cognitively stable preferred framework for describing our evolving Universe. In this frame, space is globally static, masses monotonically increase, and the space describing gravitationally bounded objects monotonically contracts. Full article