Celestial Coordinates Research Articles

Shadow of rotating black holes surrounded by dark fluid with Chaplygin-like equation of state and constraints from EHT results

Abstract The present work is devoted to testing spacetime properties around black holes surrounded by a dark fluid that are candidates for dark energy, which can be described by the Chaplygin-like equation of state through its shadow. To do this, we first study the horizon structure of the black hole and its shadow. Then, we obtain a rotating black hole solution in the presence of a dark fluid using the generalized Newman-Janis algorithm and study the effects of the black hole spin and the fluid parameters on the black hole horizons. Also, we obtain the shadow cast of the rotating black hole using celestial coordinates and have shown that the presence of the dark fluid causes an increase in shadow size. Moreover, we also obtain constraints on the spin and black hole charge together with the dark fluid parameters using the shadow size of supermassive black holes Sagittarius A* and M87* from Event Horizon Telescope observations. Finally, we also investigate the energy emission rate of the charged black hole surrounded by a Chaplygin-like dark fluid compared to both rotating and nonrotating cases.

Black hole evaporation process and Tangherlini–Reissner–Nordström black holes shadow

In this article, we study the black hole evaporation process and shadow property of the Tangherlini-Reissner-Nordström (TRN) black holes. The TRN black holes are the higher-dimensional extension of the Reissner-Nordström (RN) black holes and are characterized by their mass M, charge q, and spacetime dimensions D. In higher-dimensional spacetime, the black hole evaporation occurs rapidly, causing the black hole’s horizon to shrink. We derive the rate of mass loss for the higher-dimensional charged black hole and investigate the effect of higher-dimensional spacetime on charged black hole shadow. We derive the complete geodesic equations of motion with the effect of spacetime dimensions D. We determine impact parameters by maximizing the black hole’s effective potential and estimate the critical radius of photon orbits. The photon orbits around the black hole shrink with the effect of the increasing number of spacetime dimensions. To visualize the shadows of the black hole, we derive the celestial coordinates in terms of the black hole parameters. We use the observed results of M87 and Sgr A∗ black hole from the Event Horizon Telescope and estimate the angular diameter of the charge black hole shadow in the higher-dimensional spacetime. We also estimate the energy emission rate of the black hole. Our finding shows that the angular diameter of the black hole shadow decreases with the increasing number of spacetime dimensions D.

Shadow and quasinormal modes of novel charged rotating black hole in Born–Infeld theory: Constraints from EHT results

This work investigates the shadow and quasinormal modes of a novel rotating Born–Infeld-type black hole. First, we study the effect of interaction between nonlinear electrodynamic fields and photons on shadow radius and show that it is less than the error of shadow measurements in Event Horizon Telescope (EHT) observations. Then, we obtain a rotating metric using the Newman–Janis algorithm, starting with the initial metric of the nonrotating novel Born–Infeld black hole solution. Next, we analyze the null geodesics to determine the celestial coordinates. The black hole’s shadow radius is determined by using celestial coordinates. The mass, spin, charge, and nonlinearity parameters all influence the shape and size of the black hole shadow. An increase in the spin parameter results in a gradual reduction in the size of black hole shadows and further distortion of the shadows. Furthermore, constraints on the spin and electric charge of black holes, as well as the nonlinearity parameter, are derived through the utilization of the shadow sizes of supermassive black holes Sagittarius (Sgr) A* and M87* obtained from observations of the EHT. Also, we investigate the correlation between the standard shadow radius and the equatorial and polar quasinormal modes for revolving black holes. Finally, we analyze the emission energy rate from the black hole based on different spacetime parameters. Our observation indicates that the emission energy rate decreases as the values of spin and nonlinearity parameters increase, keeping the charge-to-mass ratios of the Born–Infeld black hole constant.

ФИЗИКАНЫ ЖАНА АСТРОНОМИЯНЫ ОКУТУУДА ЖАНА ИЗИЛДӨӨДӨ МАТЕМАТИКАНЫН ОРДУ

This scientific article is devoted to the ways of using mathematics in teaching and researching the subjects of physics and astronomy. Newton's first polynomial was used in mathematical modeling of the emission of electron and hole color centers in solid state physics. Shannon's formula was used to determine information entropy, and the logarithmic function of Boltzmann's formula was used to determine statistical entropy. In astronomy, trigonometric functions and stereographic transformations are used to determine celestial coordinates and transform very large angles. This research paper will help students in their study of these disciplines. Particular attention is paid to the close connection between mathematics and astronomy and physics.

Optical features of rotating quintessential charged black holes in de-Sitter spacetime

One of the most important and actual issues in relativistic astrophysics is testing gravity theories and obtaining constraint values for the parameters of black holes using observational data. In this research, we aimed to explore the optical features of a Kerr–Newman black hole model in the presence of a quintessential field, which may be a candidate for a dark-energy model with a nonzero cosmological constant. First, we obtain the equations of motion for photons using the Hamilton–Jacobi formalism. We also study the horizons and shapes of the apparent regions of the photon region around the said black hole. In various scenarios, we investigate shadows cast by the black hole using celestial coordinates. Furthermore, we analyze the effects of the quintessential field and black hole charge on the shadow radius and distortion. Furthermore, we look into the constraints on the spin and charge of supermassive black holes M87∗ and Sagittarius A∗ for different values of the quintessential field using their shadow size measured by the Event Horizon Telescope Collaboration. Finally, we study the effects of the quintessential field, black hole spin and charge on its energy emission rate by Hawking radiation and compare our results with those of the available literature.

Digitization of Astronomical Photographic Plates of China and Astrometric Measurement of Single-exposure Plates

From the mid-19th century to the end of the 20th century, photographic plates served as the primary detectors for astronomical observations. Astronomical photographic observations in China began in 1901, and over a century, a total of approximately 30,000 astronomical photographic plates were captured. These historical plates play an irreplaceable role in conducting long-term, time-domain astronomical research. To preserve and explore these valuable original astronomical observational data, Shanghai Astronomical Observatory has organized the transportation of plates, taken during nighttime observations from various stations across the country, to the Sheshan Plate Archive for centralized preservation. For the first time, plate information statistics were calculated. On this basis, the plates were cleaned and digitally scanned, and finally digitized images were acquired for 29,314 plates. In this study, using Gaia DR2 as the reference star catalog, astrometric processing was carried out successfully on 15,696 single-exposure plates, including object extraction, stellar identification, and plate model computation. As a result, for long focal length telescopes, such as the 40 cm double-tube refractor telescope, the 1.56 m reflector telescope at Shanghai Astronomical Observatory, and the 1m reflecting telescope at Yunnan Astronomical Observatory, the astrometric accuracy obtained for their plates is approximately 0.″1–0.″3. The distribution of astrometric accuracy for medium and short focal length telescopes ranges from 0.″3 to 1.″0. The relevant data of this batch of plates, including digitized images and a stellar catalog of the plates, are archived and released by the National Astronomical Data Center. Users can access and download plate data based on keywords such as station, telescope, observation year, and observed celestial coordinates.

How Well is the International Celestial Reference System Maintained in Official IAU Implementations?

The International Celestial Reference Frame (ICRF) based on the VLBI-derived positions of 608 extragalactic radio sources was adopted by the International Astronomical Union (IAU) in 1998 as the first realization of the International Celestial Reference System (ICRS). Later, in 2009 and 2020, two extended ICRF versions, ICRF2 and ICRF3, respectively, were released. The latter is adopted by the IAU as the current implementation of the ICRF in the radio band. In the meantime, the Gaia mission delivered three versions of the optical ICRS realization in 2016, 2018, and 2022 with an accuracy similar to that achieved by VLBI-based ICRF. The Gaia-CRF catalogs were linked to the ICRF under no-rotation conditions and thus may suffer from ICRF systematic instability if the latter is substantial. In this work, a new analysis was performed to assess the long-term stability of radio and optical ICRS realizations. Based on the 16-parameter vector spherical harmonics expansion of the differences between the three ICRF catalogs, it can be concluded that the mutual orientation between them is at a level of a few tens of microarcseconds, while the components of the glide vector and E 2,0 term are several times greater. A comparison of the three Gaia-CRF catalogs with the ICRF3-SX showed that for the latest Gaia-CRF catalog, Gaia-CRF3, all rotational and deformation components are below 20 μas except for the E 2,0 term, which is several times greater. For both ICRF and Gaia-CRF catalogs, the evolution of the source position errors is also tracked.

Shadow of novel rotating black hole in GR coupled to nonlinear electrodynamics and constraints from EHT results

We study the optical properties of spacetime around a novel black hole in general relativity coupled to nonlinear electrodynamics, which is asymptotically flat. First, we study the angular velocity and Lyapunov exponent in unstable photon circular orbits in the novel spherically symmetric black hole spacetime. Later, we obtain the rotating black hole solution using the Newman–Janis algorithm and determine the event horizon properties of the black hole. We analyze the effective potential for the circular motion of photons in the spacetime of the novel rotating black hole. Also, we analyze the photon sphere around the novel black hole and its shadow using celestial coordinates. We obtain that an increase of the black hole spin and charge as well as nonlinear electrodynamics field nonlinearity parameters causes an increase in the distortion parameter of the black hole shadow, while, the area of the shadow and its oblateness decrease. Moreover, we also obtain the constraint values for the black hole charge and the nonlinearity parameters using Event Horizon Telescope data from shadow sizes of supermassive black holes Sgr A* and M87*. Finally, the emission rate of black hole evaporation through Hawking radiation is also studied.

25 років Яворівському НГП – структура, використання, значення досліджень, перспективи

This paper presents detailed information about the stages of creation and directions of use of a special multifunctional standard scientific geodetic polygon (SGP) in Yavoriv district of Lviv region. The main purpose of the SGP is the metrological control of modern geodetic instruments and the testing of new technologies. The features of constructing geodetic networks, creating a local reference gravimetric network to refine the parameters of the global Earth gravimetric model, and constructing a quasi-geoid model with centimeter accuracy within the local polygon are described. The determination of high-precision astronomical coordinates and reference azimuths with an accuracy of 0.5–1.0, the creation of metrological objects of the NGP are outlined: the standard linear baseline (SLB) of original design and the fundamental geodetic network (FGN) for conducting special research and metrological verification of electronic theodolites, rangefinders, GNSS receivers, the development of a high-precision leveling network for studying accuracy and GNSS-leveling, etc. It provides information about multi-year experimental calibrations of the SLB using various methods and devices, and the first international intercomparisons on the SLB (working standard) in Ukraine, as well as multi-day GNSS observation campaigns at FGN points, the results of processing, and the achieved high accuracy. New experimental studies are related to improving the accuracy of FGN and GNSS leveling, new calibrations of SLB, including international intercomparisons, establishment of fundamental gravimetric points, optimization of the use of reference directions for metrological control and calibration of navigation equipment.

4D Einstein-Gauss-Bonnet black hole in Power-Yang-Mills field: a shadow study

We consider a static black hole immersed in the Power-Yang-Mills field in four-dimensional Einstein-Gauss-Bonnet gravity and investigate the effect of various parameters on the radius of the photon sphere. The modified form of the Newman-Janis algorithm is used for obtaining a rotating black hole solution in this gravity. Further, we try to explore the influence of the Yang-Mills magnetic charge Q with power q, Gauss-Bonnet parameter α, and spin a on the horizon radius. The geodesic equations are constructed by incorporating the Hamilton-Jacobi formalism. The radial component of the geodesic equations gives the effective potential which is further used in deriving the mathematical structure for the shadows by using Bardeen's procedure for a fixed observer at infinity. The shadows are calculated and plotted in terms of two celestial coordinates for an equatorial observer. It is observed that all the parameters have a very significant effect on the shadow and related physical observables. We also obtain the constraint values for the spin, magnetic charge, and Gauss-Bonnet parameters, using the shadow size of supermassive black holes Sagittarius A* and M87* from the EHT observations for the cases of q = 0.6 and q = 0.9. It is shown that there are upper and lower bounds for the charge and spin of M87* at q = 0.6, while only the upper bounds for the charge and spin of Sagittarius A*. Finally, we investigate the energy emission rate in the Hawking radiation around the 4D Einstein-Gauss-Bonnet black hole in the Power-Yang-Mills field.

Enhancing the alignment of the optically brightGaiareference frame with respect to the International Celestial Reference System

Context.The link of theGaiaframe in terms of non-rotation with respect to the International Celestial Reference System (ICRS), which is realized via very long baseline interferometry (VLBI) at radio wavelengths, has to be conducted for the wide range of optical magnitudes in which the spacecraft observes. There is a sufficient number of suitable counterparts between the two measurement systems for optically faint objects. However, the number of common optically bright (G≤ 13 mag) objects is sparse as most are faint at radio frequencies, and only a few objects suitable for astrometry have been observed by VLBI in the past. As a result, rotation parameters for the optically brightGaiareference frame are not yet determined with sufficient accuracy.Aims.The verification of theGaiabright frame of DR2 and EDR3 is enhanced by the reevaluation of existing VLBI observations and the addition of newly acquired data for a sample of optically bright radio stars.Methods.Historical data from the literature were reevaluated, ensuring that the calibrator positions and uncertainties (used for the determination of the absolute star positions in the phase-referencing analysis) were updated and homogeneously referred to the ICRF3, the third realization of the International Celestial Reference Frame. We selected 46 suitable optically bright radio stars from the literature for new radio observations, out of which 32 were detected with the VLBA in continuum mode in the X or C band, along with radio-bright calibrators in the ICRF3. ImprovedGaia-VLBI rotation parameters were obtained by adding new observations and utilizing more realistic estimates of the absolute position uncertainties for all phase-referenced radio observations.Results.The homogenization greatly improved the steadiness of the results when the most discrepant stars were rejected one after another through a dedicated iterative process. ForGaiaDR2, this homogenization reduced the magnitude of the orientation parameters to less than 0.5 mas but increased that of the spin parameters, with the largest component being the rotation around the Y axis. An adjustment of the position uncertainties improved the reliability of the orientation parameters and the goodness of fit for the iterative solutions. Introducing the new single-epoch positions to the analysis reduced the correlations between the rotation parameters. The final spin forGaiaDR2 as determined by VLBI observations of radio stars is (−0.056, −0.113, +0.033) ± (0.046, 0.058, 0.053) mas yr−1. A comparison of the new results with external, independently derived spin parameters forGaiaDR2 reveals smaller differences than when using the historical data from the literature. Applying the VLBI data toGaiaEDR3, which was already corrected for spin duringGaiaprocessing, the derived residual spin is (+0.022, +0.065, −0.016) ± (0.024, 0.026, 0.024)mas yr−1, showing that the component in Y is significant at the 2.4σlevel.Conclusions.Even though our analysis provides a more accurate frame tie, more VLBI data are needed to refine the results and reduce the scatter between iterative solutions.

Mathematical Methods for an Accurate Navigation of the Robotic Telescopes

Accurate sky identification is one of the most important functions of an automated telescope mount. The more accurately the robotic telescope is navigated to the investigated part of the sky, the better the observations and discoveries made. In this paper, we present mathematical methods for accurate sky identification (celestial coordinates determination). They include the automatic selection of the reference stars, preliminary and full sky identification, as well as an interaction with international databases, which are a part of the astrometric calibration. All described methods help to receive accurately calculated astrometric data and use it for the positional calibration and better navigation of the automated telescope mount. The developed methods were successfully implemented in the Collection Light Technology (CoLiTec) software. Through its use, more than 1600 small solar system objects were discovered. It has been used in more than 700,000 observations and successful sky identifications, during which, five comets were discovered. Additionally, the accuracy indicators of the processing results of the CoLiTec software are provided in the paper, which shows benefits of the CoLiTec software and lower standard deviation of the sky identification in the case of low signal-to-noise ratios.

Stellarium Assisted Celestial Coordinate Learning to Encourage Students’ Concept Comprehension and Digital Literacy

The aim of this work is to determine the understanding of concepts and digital literacy of students using the Stellarium application in learning astronomy, specifically the celestial body coordinates. The study used pre-experimental one-group pretest-posttest design. The sample consists of physics students at UNNES who were taking the Astronomy course. Data was collected through testing using a concept comprehension test and a digital literacy questionnaire. Due to the non-normal distribution of the data, hypothesis testing was conducted using the Wilcoxon test, which showed that the increase in students' concept comprehension was not significant (z-score = -1.43, p-value = 0.076). This result was confirmed by the N-gain of 8.71% (low). However, there were three indicators of the seven concept comprehension indicators tested, that showed a significant improvement, i.e. interpreting, exemplifying, and inferring. Rasch model analysis of the digital literacy questionnaire showed that students' digital literacy skills were very good and consistent with the model's prediction. Thus, the use of Stellarium in learning celestial coordinates can partially improve students' concept comprehension and digital literacy skills.Keywords: Stellarium, Celestial Body coordinates, concept comprehension, Digital Literacy.

Shadow of the 5D Reissner–Nordström AdS black hole

In this paper, we discuss the shadow cast by the charged Reissner–Nordström (RN) anti-de Sitter (AdS) black hole. With the help of the Killing equation and Hamilton–Jacobi equation, we calculate the geodesic equations for null particles. With the help of geodesics of null particle, we then determine the celestial coordinates ([Formula: see text], [Formula: see text]) and the shadow radius of the RN AdS black hole. We present a graphical analysis of the black hole shadow and find that shadow is a perfectly dark circle. The impacts of charge and cosmological constant of the RN AdS black hole on the radius of shadow are also presented. In this connection, the radius of the shadow is a decreasing function of the charge. Furthermore, we study the effects of plasma medium on the RN AdS black hole shadow. Here, we find that radius of circular shadow increases with increasing plasma parameter. We study the shadow radius for the constrained values of charge and cosmological constant from the [Formula: see text] and [Formula: see text] black holes. In addition, we also discuss the energy emission the rate of RN black hole. The effects of parameters like charge, cosmological constant and plasma parameter on energy emission rate are analyzed graphically.

Utilization of Sky Map Application in Astronomy Learning of Celestial Coordinates to Improve Students’ Understanding of Concepts and Digital Literacy for Physics Education Students

Using the Sky Map application in astronomy learning of celestial coordinates is intended to analyze students' level of understanding of concepts and digital literacy. Students' understanding of concepts and digital literacy was measured through tests and questionnaires. The research was focused on students who took astronomy courses in the physics department of Semarang State University, totaling 40 students. The type of research used is quantitative research. The research design carried out was pre-experimentation with one group pretest-posttest. There are two variables used, i.e. the use of Sky Map application media as the independent variable, and the improvement of the understanding of the student concept as the dependent variable. The analysis using the Wilcoxon signed rank test showed a significant increase in students' conceptual understanding after using Sky Map application media in learning with an N-Gain of 0.21, and digital literacy in the use of Sky Map application media has attained 83.47% (excellent). Therefore, it can be concluded that the use of Sky Map application media in celestial coordinates can help students understand the concept of the material as well as increase their digital literacy skills.

Tidal Effects and Clock Comparison Experiments

Einstein’s general relativity theory provides a successful understanding of the flow of time in the gravitational field. From Einstein’s equivalence principle, the influence of the Sun and Moon masses on clocks is given in the form of tidal potentials. Two clocks fixed on the surface of the Earth, compared to each other, can measure the tidal effects of the Sun and Moon. The measurement of tidal effects can provide a test for general relativity. Based on the standard general relativity method, we rigorously derive the formulas for clock comparison in the Barycentric Celestial Reference System and Geocentric Celestial Reference System, and demonstrate the tidal effects on clock comparison experiments. The unprecedented performance of atomic clocks makes it possible to measure the tidal effects on clock comparisons. We propose to test tidal effects with the laboratory clock comparisons and some international missions, and give the corresponding estimations. By comparing the state-of-the-art clocks over distances of 1000 km, the laboratory may test tidal effects with a level of 1%. Future space missions, such as the China space station and FOCOS mission, can also be used to test tidal effects, and the best accuracy may reach 0.3%.

Combining Historical, Remote-Sensing, and Photogrammetric Data to Estimate the Wreck Site of the USS Kearsarge

Colombia has hundreds of historical shipwrecks, but systematic research on this topic is scarce, which makes locating wreck sites problematic. Colombia is home to the Caribbean archipelago of San Andres, Old Providence, and Santa Catalina. Its complex environmental conditions make it a “ship trap”. On 2 February 1894, the USS Kearsarge ran aground on Roncador Cay, one of the Archipelago’s islets, and the location of the wreck site remains uncertain. Due to its role in the American Civil War, the Kearsarge is important naval heritage. Based on historical and cartographic records, orthophotographs, Landsat images, and light-detection-and-ranging (LiDAR) data, this study aimed to estimate the location of the wreck site in a Geographic Information System (GIS). Court-martial records, particularly nautical data and astronomical coordinates, were reviewed, including a study from 1894 indicating the wreck’s location on a map without coordinates. Nautical charts were also analyzed to find the Kearsarge wreck symbol. To identify the wreck site’s ordnance, logbooks and information on previous salvage efforts were examined. The analysis of nautical charts revealed a few shipwrecks, but not the Kearsarge. Historical and remote-sensing data were processed in a GIS, along with the most recent nautical chart of Roncador Cay from 2017, to obtain a possible geographical location. This resulted in coordinates, which were used to detect features associated with the USS Kearsarge in the processed data. Although the wreck was not detected, the data helped to estimate the approximate coordinates for where the wreck could be located, quantifying our degree of uncertainty.

Celestial amplitudes in an ambidextrous basis

We start by constructing a conformally covariant improvement of the celestial light transform which keeps track of the mixing between incoming and outgoing states under finite Lorentz transformations in ℝ2,2. We then compute generic 2, 3 and 4-point celestial amplitudes for massless external states in the ambidextrous basis prepared by composing this SL(2, ℝ) intertwiner with the usual celestial map between momentum and boost eigenstates. The results are non-distributional in the celestial coordinates (z, overline{z} ) and conformally covariant in all scattering channels. Finally, we focus on the tree level 4-gluon amplitude where we present a streamlined route to the ambidextrous correlator based on Grassmannian formulae and examine its alpha space representation. In the process, we gain insights into the operator dictionary and CFT data of the holographic dual.

Tycho Brahe’s observations of Præsepe Cancri

Tycho Brahe made several thousand observations of the celestial bodies, in general with an unprecedented accuracy and precision. A group of observations of a nebulous object known as Præsepe differs, however, significantly from the general picture. Over a period of 3 years, Tycho observed different astronomical coordinates for Præsepe; the values of meridian altitude differed by as much as 8 arcminutes for repeated observations, and the declination values by up to 5 arcminutes, systematic discrepancies such as these never seen before or since for Tycho’s stellar observations. In this article it will be demonstrated that these differences were due to the observation of three or four individual stars and not of a single arbitrarily defined centre in Præsepe, the open star cluster M44 as it is known today. Individual stars had not been resolved in Præsepe before, and consequently neither had their celestial coordinates been determined. Tycho selected a single of the observed stars to represent Præsepe and included its celestial coordinates in his star catalogues.

Relativistic contributions to the rotation of Mars

Context. The orientation and rotation of Mars can be described by a set of Euler angles (longitude, obliquity, and rotation angles) and estimated from radioscience data (tracking of orbiters and landers), which can then be used to infer the planet's internal properties. The data are analyzed using a modeling expressed within the barycentric celestial reference system (BCRS). This modeling includes several relativistic contributions that need to be properly taken into account to avoid any misinterpretation of the data. Aims. We provide new and more accurate (to the 0.1 mas level) estimations of the relativistic corrections to be included in the BCRS model of the orientation and rotation of Mars. Methods. There are two types of relativistic contributions with regard to Mars's rotation and orientation: (i) those that directly impact the Euler angles and (ii) those resulting from the time transformation between a local Mars reference frame and BCRS. The former contribution essentially corresponds to the geodetic effect, as well as to the smaller Lense-Thirring and Thomas precession effects, and we computed their values assuming that Mars evolves on a Keplerian orbit. As for the latter contribution, we computed the effect of the time transformation and compared the rotation angle corrections obtained, based on the assumption that the planets evolve on Keplerian orbits, with the corrections obtained, based on realistic orbits as described by the ephemerides. Results. The relativistic correction in longitude mainly comes from the geodetic effect and results in a geodetic precession (6.754 mas yr−1) and geodetic annual nutation (0.565 mas amplitude). For the rotation angle, the correction is dominated by the effect of the time transformation. The main annual, semiannual, and terannual terms display amplitudes of 166.954 mas, 7.783 mas, and 0.544 mas, respectively. The amplitude of the annual term differs by about 9 mas from the estimate usually considered by the community. We identified new terms at the Mars-Jupiter and Mars-Saturn synodic periods (0.567 mas and 0.102 mas amplitude) that are relevant considering the current level of uncertainty of the measurements, as well as a contribution to the rotation rate (7.3088 mas day−1). There is no significant correction that applies to the obliquity.