Galactic Center Research Papers - Academia.edu (original) (raw)

2025, Nature

The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation1,2. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure, which was interpreted as gravitationally lensed emission around a central black hole3. Here we report images of M87 obtained in 2018, at a wavelength of 3.5 mm, showing that the compact radio core is spatially resolved. High-resolution imaging shows a ring-like structure of {8.4}_{-1.1}^{+0.5}$$ 8.4 − 1.1 + 0.5 Schwarzschild radii in diameter, approximately 50% larger than that seen at 1.3 mm. The outer edge at 3.5 mm is also larger than that at 1.3 mm. This larger and thicker ring indicates a substantial contribution from the accretion flow with absorption effects, in addition to the gravitationally lensed ring-like emission. The images show that the edge-brightened jet connects to the accretion flow of the black hole. Close to the black hole, the emission profile of th...

2025, Astronomical & Astrophysical Transactions

Reprints availebie directly from the publisher Photocopying permitted by licenie only @ZOO1 OPA (Overwas Publishers Awocirtion) N.V.

2025, The Astrophysical Journal

The main aim of this paper is to report two new detections of tidal debris in the northern stream of the Sagittarius dwarf galaxy located at 45 • and 55 • from the center of galaxy. Our observational approach is based on deep colormagnitude diagrams, that provides accurate distances, surface brightness and the properties of stellar population of the studied region of this tidal stream. The derived distances for these tidal debris wraps are 45± 2 kpc and 54 ± 2 kpc respectively. These detections are also strong observational evidence that the tidal stream discovered by the Sloan Digitized Sky Survey is tidally stripped material from the Sagittarius dwarf and support the idea that the tidal stream completely enwraps the Milky Way in an almost polar orbit. We also confirm these detections running numerical simulations of the Sagittarius dwarf plus the Milky Way. This model reproduces the present position and velocity of the Sagittarius main body and presents a long tidal stream formed by tidal interaction with the Milky Way potential. The tidal streams of the model traces the last orbit of Sagittarius and confirms our observational detections. This model is also in good agreement with the available observations of the Sagittarius tidal stream. The comparison of our model with the positions and distances of two non-identified halo overdensities discovered by the Sloan Digitized Sky Survey and the QUEST survey shows that they are actually associated to the trailing arm of the Sagittarius tidal stream. In addition, we identify the proper motion group discovered by Arnold & Gilmore (1992) as a piece of the Sagittarius northern stream. We also present a method for estimating the shape of the Milky Way halo potential using numerical simulations. From our simulations we obtain an oblateness of the Milky Way dark halo potential of 0.85, using the current database of distances and radial velocities of the Sagittarius tidal stream. The color-magnitude diagram of the apocenter of Sagittarius shows that this region of the stream shares the complex star formation history observed in the main body of the galaxy. We present the first evidence for a gradient in the stellar population along the stream, possibly correlated with its different pericenter passages.

2025, Journal of astrophysics & aerospace technology

2025, Physical Review D

We present a model where sterile neutrinos with rest-masses in the range ∼ keV to ∼ MeV can be the dark matter and be consistent with all laboratory, cosmological, large scale structure, and X-ray constraints. These sterile neutrinos are assumed to freeze out of thermal and chemical equilibrium with matter and radiation in the very early universe, prior to an epoch of prodigious entropy generation ("dilution") from out-of-equilibrium decay of heavy particles. In this work, we consider heavy, entropy-producing particles in the ∼ TeV to ∼ EeV rest-mass range, possibly associated with new physics at high energy scales. The process of dilution can give the sterile neutrinos the appropriate relic densities, but it also alters their energy spectra so that they could act like cold dark matter, despite relatively low rest-masses as compared to conventional dark matter candidates. Moreover, since the model does not rely on active-sterile mixing for producing the relic density, the mixing angles can be small enough to evade current X-ray/lifetime constraints. Nevertheless, we discuss how future X-ray observations, future lepton number constraints, and future observations and sophisticated simulations of large scale structure could, in conjunction, provide evidence for this model and/or constrain and probe its parameters.

2025, The Open Environmental Engineering Journal

We report the first results of a research program to explore the sensitivity of the orbits of Oort cloud comets to changes in the strength of the Galactic tides in the plane of the disk and also to changes in the mass of the host star. We performed 2D simulations that confirm that the effects of the tides on comet orbits are sensitive to a star's distance from the Galactic center. A comet cloud closer to the Galactic center than the Sun will have comet perihelia reduced to the region of the inner planets more effectively by the planar tides alone. Similar results are found for a star of smaller mass. We also show how this phenomenon of comet injection persists for a set of alternative Galactic potential models. These preliminary results suggest a fruitful line of research, one that aims to generalize the study of comet cloud dynamics to systems different from the Solar System. In particular, it will allow us to study the roles played by comet clouds in defining the boundaries of the Galactic Habitable Zone.

2025, TEORIJA UKLJUČENOSTI

MATEMATIČKI I LOGIČKI DOKAZI KOJI OSPORAVAJU POSTOJANJE
UNIVERZALNE GRAVITACIJSKE KONSTANTE

2025, Physical Review D

Self-annihilating or decaying dark matter in the Galactic halo might produce high energy neutrinos detectable with neutrino telescopes. We have conducted a search for such a signal using 276 days of data from the IceCube 22-string configuration detector acquired during 2007 and 2008. The effect of halo model choice in the extracted limit is reduced by performing a search that considers the outer halo region and not the Galactic Center. We constrain any large scale neutrino anisotropy and are able to set a limit on the dark matter self-annihilation cross section of σAv ≃ 10 -22 cm 3 s -1 for WIMP masses above 1 TeV, assuming a monochromatic neutrino line spectrum.

2025, Astronomy & Astrophysics

This paper describes the response of the IceCube neutrino telescope located at the geographic south pole to outbursts of MeV neutrinos from the core collapse of nearby massive stars. IceCube was completed in December 2010 forming a lattice of 5160 photomultiplier tubes that monitor a volume of ∼1 km 3 in the deep Antarctic ice for particle induced photons. The telescope was designed to detect neutrinos with energies greater than 100 GeV. Owing to subfreezing ice temperatures, the photomultiplier dark noise rates are particularly low. Hence IceCube can also detect large numbers of MeV neutrinos by observing a collective rise in all photomultiplier rates on top of the dark noise. With 2 ms timing resolution, IceCube can detect subtle features in the temporal development of the supernova neutrino burst. For a supernova at the galactic center, its sensitivity matches that of a background-free megaton-scale supernova search experiment. The sensitivity decreases to 20 standard deviations at the galactic edge (30 kpc) and 6 standard deviations at the Large Magellanic Cloud (50 kpc). IceCube is sending triggers from potential supernovae to the Supernova Early Warning System. The sensitivity to neutrino properties such as the neutrino hierarchy is discussed, as well as the possibility to A109, page 1 of 18 detect the neutronization burst, a short outbreak of ν e 's released by electron capture on protons soon after collapse. Tantalizing signatures, such as the formation of a quark star or a black hole as well as the characteristics of shock waves, are investigated to illustrate IceCube's capability for supernova detection.

2025, The Astrophysical Journal

The Bolocam Galactic Plane Survey (BGPS) data for a six square degree region of the Galactic plane containing the Galactic center is analyzed and compared to infrared and radio continuum data. The BGPS 1.1 mm emission consists of clumps interconnected by a network of fainter filaments surrounding cavities, a few of which are filled with diffuse near-IR emission indicating the presence of warm dust or with radio continuum characteristic of HII regions or supernova remnants. New 350 µm images of the environments of the two brightest regions, Sgr A and B, are presented. Sgr B2 is the brightest mm-emitting clump in the Central Molecular Zone and may be forming the closest analog to a super star cluster in the Galaxy. The Central Molecular Zone (CMZ) contains the highest concentration of mm and sub-mm emitting dense clumps in the Galaxy. Most 1.1 mm features at positive longitudes are seen in silhouette against the 3.6 to 24 µm background observed by the Spitzer Space Telescope. However, only a few clumps at negative longitudes are seen in absorption, confirming the hypothesis that positive longitude clumps in the CMZ tend to be on the near-side of the Galactic center, consistent with the suspected orientation of the central bar in our Galaxy. Some 1.1 mm cloud surfaces are seen in emission at 8 µm, presumably due to polycyclic aromatic hydrocarbons (PAHs). A ∼0.2 • (∼30 pc) diameter cavity and infrared bubble between l ≈ 0.0 • and 0.2 • surrounds the Arches and Quintuplet clusters and Sgr A. The bubble contains several clumpy dust filaments that point toward Sgr A * ; its potential role in their formation is explored. Bania's Clump 2, a feature near l = 3 • to 3.5 • which exhibits extremely broad molecular emission lines (∆V > 150 km s -1 ), contains dozens of 1.1 mm clumps. These clumps are deficient in near-and mid-infrared emission in the Spitzer images when compared to both the inner Galactic plane and the Central Molecular Zone. Thus, Bania's Clump 2 is either inefficient in forming stars or is in a pre-stellar phase of clump evolution. The Bolocat catalog of 1.1 mm clumps contains 1428 entries in the Galactic center between l = 358.5 • to l = 4.5 • of which about 80% are likely to be within about 500 pc of the center. The mass-spectrum above about 80 M ⊙ can be

2025, Astronomy & Astrophysics

Context. The recent and exquisite astrometric, photometric, and radial velocity measurements of the Gaia mission resulted in a substantial advancement of the determination of the orbits for old star clusters, including the oldest Milky Way globular clusters (MW GCs). Aims. The main goal of the present paper is to use the new Gaia data release 3 (DR3) and the VISTA Variables in the Via Láctea Extended Survey (VVVX) measurements to obtain the orbits for nearly a dozen new MW GC candidates that have been poorly studied or previously unexplored. Methods. We use the Gaia DR3 and VVVX databases to identify bona fide MW GC candidates, namely VVV-CL160, Patchick 122, Patchick 125, Patchick 126, Kronberger 99, Kronberger 119, Kronberger 143, ESO 92-18, ESO 93-08, Gaia 2, and Ferrero 54. The relevant mean cluster physical parameters are derived (distances, Galactic coordinates, proper motions, radial velocities). We also measure accurate mean radial velocities for the GCs VVV-CL160 and Patchi...

2025, Journal of Cosmology and Astroparticle Physics

We consider the possibility that the dark matter, which is required to explain the dynamics of the neutral hydrogen clouds at large distances from the galactic center, could be in the form of a Bose-Einstein condensate. To study the condensate we use the non-relativistic Gross-Pitaevskii equation. By introducing the Madelung representation of the wave function, we formulate the dynamics of the system in terms of the continuity equation and of the hydrodynamic Euler equations. Hence dark matter can be described as a non-relativistic, Newtonian Bose-Einstein gravitational condensate gas, whose density and pressure are related by a barotropic equation of state. In the case of a condensate with quartic non-linearity, the equation of state is polytropic with index n = 1. In the framework of the Thomas-Fermi approximation the structure of the Newtonian gravitational condensate is described by the Lane-Emden equation, which can be exactly solved. General relativistic configurations with quartic non-linearity are studied, by numerically integrating the structure equations. The basic parameters (mass and radius) of the Bose-Einstein condensate dark matter halos sensitively depend on the mass of the condensed particle and of the scattering length. To test the validity of the model we fit the Newtonian tangential velocity equation of the model with a sample of rotation curves of low surface brightness and dwarf galaxies, respectively. We find a very good agreement between the theoretical rotation curves and the observational data for the low surface brightness galaxies. The deflection of photons passing through the dark matter halos is also analyzed, and the bending angle of light is computed. The bending angle obtained for the Bose-Einstein condensate is larger than that predicted by standard general relativistic and dark matter models. The angular radii of the Einstein rings are obtained in the small angles approximation. Therefore the study of the light deflection by galaxies and the gravitational lensing could discriminate between the Bose-Einstein condensate dark matter model and other dark matter models.

2025, Modern Capture of Black holes

Black holes have long stood as some of the most mysterious and fascinating entities in the universe. Once regarded purely as theoretical constructs derived from Einstein's equations, black holes are now among the most intensely studied and even visually represented cosmic phenomena. The idea of "capturing" a black hole does not involve physically containing it, but rather understanding, observing, and imaging it using advanced scientific tools. In the modern era, breakthroughs in astrophysics, data analysis, and observational technology have allowed humanity to achieve what once seemed impossible: visualizing the unseeable. Black holes, by their nature, absorb all light and energy that enters past their event horizon, meaning that they do not reflect or emit light in a way that typical celestial bodies do. Despite this, their presence can be inferred through the effects they exert on their surroundings. Stars orbiting unseen massive centers, jets of radiation being ejected from galactic cores, and more recently, the detection of gravitational waves-all of these phenomena are traces left by black holes. But in 2019, history was made when the Event Horizon Telescope (EHT), a global collaboration of observatories, successfully produced the first-ever image of a black hole located in the galaxy M87. This marked a fundamental milestone not only in astronomy but in our collective ability to push the boundaries of observational science.

2025, Astronomische Nachrichten

The estimation of the main parameters of star clusters is significant in astrophysical studies. The most important aspect of using the Gaia DR2 survey lies in the positions, parallax, and proper motions of cluster stars with homogeneous photometry that make the membership probability determine with high accuracy. In this respect, depending on Gaia DR2 database, an analysis of the open star cluster Melotte 72 is taking place here. It is located at a distance of 2345±108 pc with an age of 1.0±0.5 Gyr. In studying the radial density profile, the radius is found to be 5.0±0.15 arcmin. The reddening, the luminosity and mass functions, the total mass of the cluster, and the galactic geometrical distances (X⊙, Y⊙, Z⊙), and the distance from the galactic center (Rg) have been estimated as well. Our study has shown a dynamical relaxation behavior of Melotte 72.

2025

The Chalonge 16th Paris Cosmology Colloquium (25-27 July 2012) in the historic Paris Observatory's Perrault building, combined in the Chalonge School spirit real cosmological/astrophysical data and hard theory predictive approach connected to them in the framework of the Warm Dark Matter Standard Model of the Universe:Theory and Observations : News and reviews from Atacama Cosmology Telescope (ACT) and WMAP, South Pole Telescope (SPT), Herschel, QUIET, Planck, JWST, UFFO, KATRIN and MARE experiments; astrophysics, particle physics and nuclear physics warm dark matter (WDM) searches and galactic observations, related theory and simulations, with the aim of synthesis, progress and clarification.

2025, The Astronomical Journal

High angular resolution J, H, K, and L images are used to investigate the stellar content within 6 arcsec of SgrA*. The data, which are complete to K ∼ 16, are the deepest multicolor observations of this region published to date. The mean locus of the (K, H -K) CMD varies across the field, a result that is attributed to differential reddening with amplitude ∆A V ∼ 15 mag. The reddening variations within 3 arcsec of SgrA* are significantly smaller than this, and the resolved members of the compact star cluster immediately surrounding SgrA* have photometric properties that are not significantly different from objects at larger radii. We find that sources in our field with published 2µm spectra showing either line emission or CO absorption occupy different sequences on the (K, J -K) CMD. The emission line stars, which fall along the most richly populated sequence, have redder J -K colors than stars in the Magellanic Clouds with similar spectroscopic characteristics, and evidence is presented that this is due to excess infrared emission in the spectrum of the GC sources. The photometric properties of the giant branch, which is defined by stars showing CO absorption, are similar to those of the giant branch in Baade's Window (BW). The mean J -K color and peak K brightness of the red giant branch are both consistent with a metal-rich population having an age ∼ 10 Gyr, while the width of the giant branch on the (K, J -K) CMD is indicative of an age spread ∆log(t) ≤ 1 dex. Therefore, if the inner bulge contains an underlying population of stars with ages in excess of ∼ 10 Gyr, as is the case in BW, then the region within a few arcsec of SgrA* cannot contain a large population of giant branch stars younger than 1 Gyr. We also report the detection of a modest population of faint, blue sources with K ≥ 14. We speculate that these are bright main sequence stars at the distance of the GC, although spectra will be required to confirm this interpretation. Nevertheless, the photometric properties of the largely unresolved compact knot of stars immediately surrounding SgrA* provide indirect evidence to support the presence of a large population of faint blue stars. In particular, we confirm previous studies that measure a relatively blue color for this cluster.

2025, arXiv (Cornell University)

INTEGRAL/SPI has recently observed a strong and extended emission resulting from electron-positron annihilation located in the Galactic center region, consistent with the Galactic bulge geometry, without a high energy gamma-ray counterpart, nor in the 1809 keV 26 Al decay line. In order to explain the rate of positron injection in the Galactic bulge, estimated to more than 10 43 s -1 , the most commonly considered positron injection sources are type Ia supernovae. However, SN Ia rate estimations show that those sources fall short of explaining the observed positron production rate, raising a challenging question about the nature of the Galactic positron source. In this context, a possible source of Galactic positrons could be supernova events of a new type, as the recently observed SN2003dh/GRB030329, an exploding Wolf-Rayet star (type Ic supernova) associated with a hypernova/gamma-ray burst; the question about the rate of this kind of events remains open, but could be problematically low. In this paper, we explore the possibility of positron production and escape by such an event in the framework of an asymmetric model, in which a huge amount of 56 Ni is ejected in a cone with a very high velocity; the ejected material becomes quickly transparent to positrons, which spread out in the interstellar medium.

2025, Proceedings of the International Astronomical Union

The Galactic center supermassive black hole is surrounded by orbiting clouds of gas. These clumps of gas may collide with each other, losing angular momentum and plunging towards the center. Observations of X-ray reflection from molecular clouds surrounding the Galactic center show evidence for enhanced activity of Sagittarius A* during the past few hundred years. These observations enable us to place constraints on the nature of past accretion events responsible for this enhanced activity. We model the source intrinsic luminosity of Sgr A* using multiple accretion events occurring at various moments in time, characterized by a range of angular momentum We also applied our scheme to the case of G2 cloud in the Galactic center.

2025, Успехи Физических Наук

³ÑAEÇÓÉÂÐËÇ 1. £ÄÇAEÇÐËÇ (409). 2. ªÊÎÖÚÇÐËÇ ÒÑÅÓÂÐËÚÐÑÅÑ ÔÎÑâ (412). 3. ´ÇÑÓËâ ÒÑÅÓÂÐËÚÐÑÅÑ ÔÎÑâ (415). 4. ¯ÂÃÎáAEÇÐËâ ËÊÎÖÚÇÐËâ ÒÑÅÓÂÐËÚÐÑÅÑ ÔÎÑâ Ä ÅÂÎÂÍÕËÚÇÔÍËØ ÓÇÐÕ-ÅÇÐÑÄÔÍËØ AEÄÑÌÐÞØ ÊÄÈÊAEÐÞØ ÔËÔÕÇÏÂØ (419). 5. ©ÂÍÎáÚÇÐËÇ (421).... more

2025, Galaxies

The LINER galaxy NGC 1052 is an ideal target to study the innermost regions of active galactic nuclei (AGN), given its close distance of about 20 Mpc. The source was observed at 29 epochs from 2005 to 2009 with the Very Long Baseline Array (VLBA) at 43 GHz. Here, we present a kinematic study of its twin-jet system from a subset of 9 epochs at 43 GHz carried out in 2005 and 2006, finding a bright central feature as the dynamic center. The resulting mean velocities of β = v/c = 0.46 ± 0.08 and β = 0.69 ± 0.02 for the western and eastern jet, respectively, give hints towards higher velocities in the eastern jet.

2025, Physical Review D

We present a directed search for continuous gravitational wave (CW) signals emitted by spinning neutron stars located in the inner parsecs of the Galactic Center (GC). Compelling evidence for the presence of a numerous population of neutron stars has been reported in the literature, turning this region into a very interesting place to look for CWs. In this search, data from the full O3 LIGO-Virgo run in the detector frequency band ½10; 2000 Hz have been used. No significant detection was found and 95% confidence level upper limits on the signal strain amplitude were computed, over the full search band, with the deepest limit of about 7.6 × 10 -26 at ≃142 Hz. These results are significantly more constraining than those reported in previous searches. We use these limits to put constraints on the fiducial neutron star ellipticity and r-mode amplitude. These limits can be also translated into constraints in the black hole mass-boson mass plane for a hypothetical population of boson clouds around spinning black holes located in the GC.

2025, Journal of Physics: Conference Series

We report on recent near-infrared (NIR) and X-ray observations of Sagittarius A* (Sgr A*), the electromagnetic manifestation of the ∼4×10 6 M⊙ super-massive black hole (SMBH) at the Galactic Center. The goal of these coordinated multi-wavelength observations is to investigate the variable emission from Sgr A* in order to obtain a better understanding of the underlying physical processes in the accretion flow/outflow. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope (July 2005, May 2007) and the ACIS-I instrument aboard the Chandra Xray Observatory (July 2005). We report on a polarized NIR flare synchronous to a 8×10 33 erg/s X-ray flare in July 2005, and a further flare in May 2007 that shows the highest sub-flare to flare contrast observed until now. The observations can be interpreted in the framework of a model involving a temporary disk with a short jet. In the disk component flux density variations can be explained due to hot spots on relativistic orbits around the central SMBH. The variations of the sub-structures of the May 2007 flare are interpreted as a variation of the hot spot structure due to differential rotation within the disk.

2025, Research in Astronomy and Astrophysics

Hyper-velocity stars are believed to be ejected out from the Galactic center through dynamical interactions between (binary) stars and the central massive black hole(s). In this paper, we report 19 low mass F/G/K type hyper-velocity star candidates from over one million stars of the first data release of the LAMOST general survey. We determine the unbound probability for each candidate using a Monte-Carlo simulation by assuming a non-Gaussian proper-motion error distribution, Gaussian heliocentric distance and radial velocity error distributions. The simulation results show that all the candidates have unbound possibilities over 50% as expected, and one of them may even exceed escape velocity with over 90% probability. In addition, we compare the metallicities of our candidates with the metallicity distribution functions of the Galactic bulge, disk, halo and globular cluster, and conclude that the Galactic bulge or disk is likely the birth place for our candidates.

2025, The Astrophysical Journal

Hypervelocity stars are believed to be ejected out from the Galactic center through dynamical interactions of (binary) stars with the central massive black hole(s). In this letter, we report 13 metal-poor F-type hypervelocity star candidates selected from 370,000 stars of the data release 7 of the Sloan Digital Sky Survey. With a detailed analysis of the kinematics of these stars, we find that seven of them were likely ejected from the Galactic center (GC) or the Galactic disk, four neither originated from the GC nor the Galactic disk, and the other two were possibly ejected from either the Galactic disk or other regions. Those candidates which unlikely originated from the GC or the Galactic disk, may be explained by other mechanisms, like the tidal disruption of the Milky Way's dwarf galaxies in the Galactic potential, or the gravitational interactions with a massive black hole at the center of M31 or M32.

2025, A&A

We present ISO observations of the S(0), S(1), S(2), and S(3) rotational lines of molecular hydrogen from two molecular clouds near the Galactic Center (GC). We have also measured continuum dust emission at infrared wavelengths with ISO and the rotational radio lines J=1-0 of 13 CO and C 18 O and J=2-1 of C 18 O with the IRAM-30m telescope. Using the dust continuum spectra and the CO lines we derive a total visual extinction of ∼ 15-20 magnitudes toward these GC clouds. After correcting the H 2 data for extinction, the gas temperatures are ∼ 250 K and the column densities of warm gas are ∼ 2 × 10 21 cm -2 . This is the first direct measure of the H 2 column densities of the warm component; with this, we estimate an NH 3 abundance in the warm gas of ∼ 2 10 -7 . The column density of warm gas is, at least, a factor of 100 larger than the corresponding column densities derived from the warm dust. The observed ortho-to-para ratio (OTPR) is ∼ 1, clearly below the local thermodynamical equilibrium (LTE) OTPR for gas at 250 K of ∼ 3. Low velocity shocks (∼ 10 km s -1 ) are the most likely explanation for the column densities of warm gas and dust and the non-LTE H 2 OTPR.

2025, The Astrophysical Journal

The inner ∼200 pc region of the Galaxy contains a 4 million M⊙ supermassive black hole (SMBH), significant quantities of molecular gas, and star formation and cosmic-ray energy densities that are roughly two orders of magnitude higher than the corresponding levels in the Galactic disk. At a distance of only 8.2 kpc, the region presents astronomers with a unique opportunity to study a diverse range of energetic astrophysical phenomena, from stellar objects in extreme environments, to the SMBH and star-formation-driven feedback processes that are known to influence the evolution of galaxies as a whole. We present a new survey of the Galactic center conducted with the South African MeerKAT radio telescope. Radio imaging offers a view that is unaffected by the large quantities of dust that obscure the region at other wavelengths, and a scene of striking complexity is revealed. We produce total-intensity and spectral-index mosaics of the region from 20 pointings (144 hr on-target in tota...

2025, Monthly Notices of the Royal Astronomical Society

We present a novel method for constraining the length of the Galactic bar using 6D phase space information to directly integrate orbits. We define a pseudo-length for the Galactic bar, named R Freq , based on the maximal extent of trapped bar orbits. We find the R Freq measured from orbits is consistent with the R Freq of the assumed potential only when the length of the bar and pattern speed of said potential is similar to the model from which the initial phase-space coordinates of the orbits are derived. Therefore, one can measure the model's or the Milky Way's bar length from 6D phasespace coordinates by determining which assumed potential leads to a self-consistent measured R Freq . When we apply this method to ≈210,000 stars in APOGEE DR17 and Gaia eDR3 data, we find a consistent result only for potential models with a dynamical bar length of ≈3.5 kpc. We find the Milky Way's trapped bar orbits extend out to only ≈3.5 kpc, but there is also an overdensity of stars at the end of the bar out to 4.8 kpc which could be related to an attached spiral arm. We also find that the measured orbital structure of the bar is strongly dependent on the properties of the assumed potential.

2025, arXiv (Cornell University)

General relativistic deflection of light by mass, dipole, and quadrupole moments of gravitational field of a moving massive planet in the Solar system is derived in the approximation of the linearized Einstein equations. All terms of order 1 µas are taken into account, parametrized, and classified in accordance with their physical origin. We discuss the observational capabilities of the near-future optical and radio interferometers for detecting the Doppler modulation of the radial deflection, and the dipolar and quadrupolar light-ray bendings by Jupiter and the Saturn.

2025, Dynamic Gravitational Coupling – A New Model for Galaxy Rotation without Dark Matter

Dynamic Gravitational Coupling (DGC) is a novel theoretical approach to explain the flat rotation curves of galaxies without invoking dark matter.
Instead of assuming gravity acts solely from the galactic center, DGC proposes a dynamic chain of gravitational influence between stars — comparable to a system of interconnected gears.
The theory is supported by mathematical modeling and simulation data from five real galaxies (including NGC 3198 and UGC 2885), demonstrating strong alignment with observational rotation curves.
DGC offers a new perspective on gravitational interaction at galactic scales and invites further investigation from the astrophysical community.

2025

In this note we discuss preliminary studies concerning a large-diameter gamma-ray telescope, to be part of an array of telescopes installed at the existing observation site on the Canary island of La Palma. One of the telescopes in the array will be MAGIC, presently the largest existing gamma ray telescope and the most performant world wide at low energy. A second telescope of the same class is under construction. Eventually, we will want to install one or more devices giving access to even lower gamma-ray energy; they will be larger than MAGIC by roughly a linear factor two, and are code-named ECO-1000 (for a mirror surface of 1000 m). A lower energy threshold is the key to new understanding in the gamma-ray domain observable by ground-based Cherenkov telescopes. It will allow to cover wavelengths in overlap with foreseen (and past) satellite experiments. We discuss below the substantial physics potential made available by a lower energy threshold. We also show how larger telescope...

2025, American Astronomical Society Meeting Abstracts

We present the first Laser Guide Star Adaptive Optics (LGS-AO) observations of the Galactic center. LGS-AO has dramatically improved the quality and robustness with which high angular resolution infrared images of the Galactic center can be obtained with the W. M. Keck II 10-meter telescope. Specifically, Strehl ratios of 0.7 and 0.3 at L'[3.8 µm] and K'[2.1 µm], respectively, are achieved in these LGS-AO images; these are at least a factor of two higher and a factor of four to five more stable against atmospheric fluctuations than the Strehl ratios delivered thus far with the Keck Natural Guide Star AO system on the Galactic center. Furthermore, these observations are the first that cover a large area (76 ′′ × 76 ′′ ) surrounding the central black hole at diffractionlimited resolution for an 8-10 meter class telescope. During our observations, the infrared counterpart to the central supermassive black hole, Sgr A*-IR, showed significant infrared intensity variations, with observed L' magnitudes ranging from 12.6 to 14.5 mag and a decrease in flux density of a factor of two over an 8 minute interval. The faintest end of our L' detections, 1.3 mJy (dereddened), is the lowest level of emission yet observed for this source by a factor of 3. No significant variation in the location of SgrA*-IR is detected as a function of either wavelength or intensity. Previous claims of such positional variations are easily attributable to a nearby (0. ′′ 09 or 720 AU, projected), extended, very red source, which we suggest arises from a locally heated dust feature. Near a peak in its intensity, we obtained the first measurement of SgrA*-IR's K'-L' color; its K'-L' of 3.0 ± 0.2 mag (observed) or 1.4 ± 0.2 (dereddened) corresponds to an intrinsic spectral index of α -0.5 ± 0.3 for F ν ∼ ν α . This is significantly bluer than other recent infrared measurements from the literature, which suggest α = -4 ± 1. Because our measurement was taken at a time when Sgr A* was ∼6 times brighter in the infrared than the other measurements, we posit that the spectral index of the emission arising from the vicinity of our Galaxy's central black hole may depend on the strength of the flare, with stronger flares giving rise to a higher fraction of high energy electrons in the emitting region.

2025, American Astronomical Society Meeting Abstracts #200

The recent detection of a 3-hr X-ray flare by the Chandra Observatory has raised the possibility of enhanced emission over a broad range of wavelengths from Sgr A*, the suspected 2.6 x 10 6 M ⊙ black hole at the Galactic Center, during a flaring event. We have, therefore, reconstructed 3-hr data sets from 2µm speckle and adaptive optics images (θ core = 50 -100 mas) obtained with the W. M. Keck 10-m telescopes between 1995 and 2001. In 25 separate observations, no evidence of any significant excess emission associated with Sgr A* was detected. The lowest of our detection limits gives an observed limit for the quiescent state of Sgr A* of 0.09±0.005 mJy, or, equivalently, a dereddened value of 2.0±0.1 mJy, which is a factor of 2 lower than the best previously published quiescent value. Under the assumption that there are random 3-hr flares producing both enhanced X-ray and near-infrared emission, our highest limit constrains the variable state of Sgr A* to 0.8 mJy (observed) or 19 mJy (dereddened). These results suggest that the model favored by , in which the flare is produced through local heating of relativistic particles surrounding Sgr A* (e.g., a sudden magnetic reconnection event), is unlikely, because it predicts peak 2µm emission of ∼300 mJy, well above our detection limit.

2025, Astronomy Letters

An X-ray survey of the Galactic center region with a radius of ∼20 • has been performed using the data obtained with the JEM-X telescope onboard the INTEGRAL observatory over ∼10 years of observations (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013). The exposure at the field center directly toward the Galactic center has reached 4.8 Ms. We have constructed sky maps in the 5-10 and 10-25 keV energy bands and compiled a catalog of detected sources. Together with 83 sources revealed on the integral sky maps, it includes 22 transients that are absent on them but are confidently detected during outbursts with a duration of several days. One of the persistent sources, IGR J17452-2909, has never been observed previously. In contrast to the catalog of sources detected in the harder energy band by the IBIS/ISGRI telescope onboard the INTEGRAL observatory, most of the sources in this catalog are low-mass X-ray binaries (73 of the 105 sources) and only 18 + 3 are high-mass X-ray binaries and cataclysmic variables. Out of the Galactic sources, there are also the black hole candidate XTE J1652-453, the peculiar X-ray burster XMM J174457-2850.3, and the soft gamma repeater SGR 1806-20 in the catalog; out of the extragalactic sources, there are three active galactic nuclei and a galaxy cluster (Oph CL). The nature of four sources, including the newly discovered one, still remains unknown. We have constructed the luminosity function for the low-mass X-ray binaries from the catalog and considered other statistical properties of their sample.

2025, Astronomy Letters

The detection of GRB 070912 recorded in the field of view of the SPI, IBIS/ISGRI, and JEM-X telescope on September 12, 2007, at 07 h 32 m 19 s (UT) when analyzing the INTEGRAL archival data is reported. The burst is one of the well-localized events closest to the direction toward the Galactic center (less than 1 • .6 from the source Sgr A * ) over the entire history of burst observations. Since it was not promptly revealed by the INTEGRAL Burst Alert System (IBAS), no information about its coordinates was disseminated and no search for optical and soft X-ray afterglows was conducted. The 3-200 keV fluence was 2.8 × 10 -6 erg cm -2 and the peak flux was 1.8 × 10 -7 erg cm -2 s -1 (1.9 ph cm -2 s -1 ). The burst was also observed in the KONUS/WIND experiment in the background mode, although it was not included in the list of recorded bursts. GRB 070912 is among a limited number of events for which a broadband (3 keV-2 MeV) spectrum of X-ray and gamma-ray emission has been obtained and their evolution from the first instants to complete decay has been traced. It shows how the fast evolution of its spectrum gives rise to absorption features at energies of ∼100 keV. Within the first seconds after the onset of the burst, its spectrum was a power law with a photon index of ∼0.8, but it exhibited a noticeable deficit of photons at energies below 20 keV. Such an initial deficit (a delay in appearance) of X-ray photons can be explained by their "high-latitude" origin relative to the line of sight. The spectrum rapidly softened and at the decay phase was well described by a blackbody (or Wien) law. This allows the distance (redshift) to the burst source to be estimated.

2025, The Astrophysical Journal

We have discovered a star, SDSS J090745.0+024507, leaving the Galaxy with a heliocentric radial velocity of +853 ± 12 km s -1 , the largest velocity ever observed in the Milky Way halo. The star is either a hot blue horizontal branch star or a B9 main sequence star with a heliocentric distance ∼55 kpc. Corrected for the solar reflex motion and to the local standard of rest, the Galactic rest-frame velocity is +709 km s -1 . Because its radial velocity vector points 173.8 • from the Galactic center, we suggest that this star is the first example of a hyper-velocity star ejected from the Galactic center as predicted by Hills and later discussed by Yu & Tremaine. The star has [Fe/H]∼0, consistent with a Galactic center origin, and a travel time of 80 Myr from the Galactic center, consistent with its stellar lifetime. If the star is indeed traveling from the Galactic center, it should have a proper motion of 0.3 mas yr -1 observable with GAIA. Identifying additional hyper-velocity stars throughout the halo will constrain the production rate history of hyper-velocity stars at the Galactic center.

2025

We use 2MASS photometry to select blue horizontal branch (BHB) candidates covering the sky |b| > 15 • . A 12.5 < J 0 < 15.5 sample of BHB stars traces the thick disk and inner halo to d ⊙ ≃ 9 kpc, with a density 3-5 times that of M giant stars. We base our sample selection strategy on the Century Survey Galactic Halo Project, a survey that provides a complete, spectroscopically-identified sample of blue stars to a similar depth as the 2MASS catalog. We show that a -0.20 < (J -H) 0 < 0.10, -0.10 < (H -K) 0 < 0.10 color-selected sample of stars is 65% complete for BHB stars, and is composed of 47% BHB stars. We apply this photometric selection to the full 2MASS catalog, and see no spatial overdensities of BHB candidates at high Galactic latitude |b| > 50 • . We insert simulated star streams into the data and conclude that the high Galactic latitude BHB candidates are consistent with having no ∼ 5 • wide star stream with density greater than 0.33 objects deg -2 at the 95% confidence level. The absence of structure suggests there have been no major accretion events in the inner halo in the last few Gyr. However, at low Galactic latitudes a two-point angular correlation analysis reveals structure on angular scales θ 1 • . This structure is apparently associated with stars in the thick disk, and has a physical scale of 10-100 pc. Interestingly, such structures are expected by cosmological simulations that predict the majority of the thick disk may arise from accretion and disruption of satellite mergers.

2025, The Astrophysical Journal

Hypervelocity stars (HVSs) travel with velocities so extreme that dynamical ejection from a massive black hole is their only suggested origin. Following the discovery of the first HVS by Brown and collaborators, we have undertaken a dedicated survey for more HVSs in the Galactic halo and present here the resulting discovery of two new HVSs: SDSS J091301.0ϩ305120 and SDSS J091759.5ϩ672238, traveling with Galactic rest-frame velocities of at least ϩ558 ‫ע‬ 12 and ϩ638 ‫ע‬ 12 km s Ϫ1 , respectively. Assuming the HVSs are B8 mainsequence stars, they are at distances of ∼75 and ∼55 kpc, respectively, and have travel times from the Galactic center consistent with their lifetimes. The existence of two B8 HVSs in our 1900 deg 2 survey, combined with the Yu & Tremaine HVS rate estimates, is consistent with HVSs drawn from a standard initial mass function but inconsistent with HVS drawn from a truncated mass function like the one in the top-heavy Arches cluster. The travel times of the five currently known HVSs provide no evidence for a burst of HVSs from a major infall event at the Galactic center in the last ∼160 Myr.

2025

This paper presents the analysis of the impact of public roads development on the structure of parcels, as well as on land and buildings cadastral data. The analysis was performed on land cadastre documentation in which the public roads development had been made under the provisions of special act on preparation and permission for public roads development, as well the geodetic documentation prepared for the process. The analysis shows that such a documentation prepared for the process based on the special act results in land cadastre data update. The road development process causes changes not only in the cadastral records but also in land parcels (within the farm) configuration.

2025, Journal of Cosmology and Astroparticle Physics

We provide an updated assessment of the power of the Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at the TeV scale, via the associated gamma-ray signal from pair-annihilating dark matter particles in the region around the Galactic centre. We find that CTA will open a new window of discovery potential, significantly extending the range of robustly testable models given a standard cuspy profile of the dark matter density distribution. Importantly, even for a cored profile, the projected sensitivity of CTA will be sufficient to probe various well-motivated models of thermally produced dark matter at the TeV scale. This is due to CTA's unprecedented sensitivity, angular and energy resolutions, and the planned observational strategy. The survey of the inner Galaxy will cover a much larger region than corresponding previous observational campaigns with imaging atmospheric Cherenkov telescopes. CTA will map with unprecedented precision the large-scale di...

2025

Two muon telescopes to study solar events and climate changes are currently under construction in Campinas and Niteroi, Brazil. These telescopes are located in the South Atlantic Magnetic Anomaly and will measure muon flux. The single apparatus consists of four detectors arranged to detect vertical muons and 45 degrees inclined muons from East or West. Each detector uses a plastic scintillator slab, 150x75x5cm3, and 130 mm photomultiplier assembled into a trapezoidal container. In this paper, we illustrate the main features of the telescopes, electronics and data acquisition.

2025

The AMANDA-II data collected during the period 2000-2003 have been analysed in a search for a diffuse flux of high-energy extra-terrestrial muon neutrinos from the sum of all sources in the Universe. With no excess events seen, an upper limit of E 2 ν × dNν /dEν < 7.4×10 -8 GeV cm -2 s -1 sr -1 was obtained. The sensitivity of the diffuse analysis of IceCube 9 string for 137 days of data is calculated to be E 2 ν × dNν /dEν < 1.3 × 10 -7 GeV cm -2 s -1 sr -1 . No excess events are observed, which confirms the AMANDA-II upper limit.

2025, arXiv (Cornell University)

We present the results of a λ20 cm VLA 2 observation of the compact Galactic center radio source Sgr A * . The scatter-broadened image is elongated in the East-West direction, with an axial ratio of 0.6±0.05 and a position angle of 87 0 ±3 0 . A similar shape and orientation has been found previously at shorter wavelengths using VLBI and VLBA. Both the major and minor axes follow the λ 2 law appropriate for scattering by turbulence in the intervening medium. Assuming that the anisotropy is caused by a magnetic field permeating the scattering medium, we argue that the scattering occurs within extended HII regions lying in the central 100 pc of the Galaxy. The magnetic field in this region must be poloidal, organized and is estimated to have a strength of at least 30 to 100 µGauss.

2025, arXiv (Cornell University)

Context. Our Galaxy hosts at its dynamical center Sgr A*, the closest supermassive black hole. Surprisingly, its luminosity is several orders of magnitude lower than the Eddington luminosity. However, the recent observations of occasional rapid X-ray flares from Sgr A* provide constraints on the accretion and radiation mechanisms at work close to its event horizon. Aims. Our aim is to investigate the flaring activity of Sgr A* and to constrain the physical properties of the X-ray flares. Methods. In Spring 2007, we observed Sgr A* with XMM-Newton with a total exposure of ∼230 ks. We have performed timing and spectral analysis of the new X-ray flares detected during this campaign. To study the range of flare spectral properties, in a consistent manner, we have also reprocessed, using the same analysis procedure and the latest calibration, archived XMM-Newton data of previously reported rapid flares. The dust scattering was taken into account during the spectral fitting. We also used Chandra archived observations of the quiescent state of Sgr A* for comparison. Results. On April 4, 2007, we observed for the first time within a time interval of roughly half a day, an enhanced incidence rate of X-ray flaring, with a bright flare followed by three flares of more moderate amplitude. The former event represents the second brightest X-ray flare from Sgr A* on record with a peak amplitude of about 100 above the quiescent luminosity. This new bright flare exhibits similar light-curve shape (nearly symmetrical), duration (∼3 ks) and spectral characteristics to the very bright flare observed in October 3, 2002 by XMM-Newton. The measured spectral parameters of the new bright flare, assuming an absorbed power law model taken into account dust scattering effect, are N H = 12.3 +2.1 -1.8 × 10 22 cm -2 and Γ = 2.3± 0.3 calculated at the 90% confidence level. The spectral parameter fits of the sum of the three following moderate flares, while lower (N H = 8.8 +4.4 -3.2 × 10 22 cm -2 and Γ = 1.7 +0.7 -0.6 ), are compatible within the error bars with those of the bright flares. The column density found, for a power-law model taking into account the dust scattering, during the flares is at least two times higher than the value expected from the (dust) visual extinction toward Sgr A* (A V ∼ 25 mag), i.e., 4.5 × 10 22 cm -2 . However, our fitting of the Sgr A* quiescent spectra obtained with Chandra, for a power-law model taking into account the dust scattering, shows that an excess of column density is already present during the non-flaring phase. Conclusions. The two brightest X-ray flares observed so far from Sgr A* exhibited similar soft spectra.

2025, Arxiv preprint astro-ph/ …

A. Goldwurm1,2, G. Bélanger1,2, P. Goldoni1,2, J. Paul1,2, R. Terrier1,2, M. Falanga1, P. Ubertini3, A. Bazzano3, M. Del Santo3, C. Winkler4, AN Parmar4, E. Kuulkers4, K. Ebisawa5, JP Roques6, G. Skinner6, N. Lund7, F. Melia8, and F.... more