{"topic":"black-hole-physics","sort":"top","limit":25,"offset":0,"count":25,"papers":[{"id":"arxiv:1906.11238","kind":"article","title":"First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole","authors":["Kazunori Akiyama","A. Alberdi","W. Alef","Keiichi Asada","Rebecca Azulay","Anne-Kathrin Baczko","David R. Ball","Mislav Baloković","John Barrett","Dan Bintley","Lindy Blackburn","W. Boland","Katherine L. Bouman","Geoffrey C. Bower","Michael Bremer","Christiaan D. Brinkerink","Roger Brissenden","S. Britzen","Avery E. Broderick","Dominique Broguière","Thomas Bronzwaer","Do‐Young Byun","J. E. Carlstrom","Andrew Chael","Chi‐kwan Chan"],"author_count":100,"year":2019,"published":"2019-04-09","venue":"The Astrophysical Journal Letters","cited_by":4205,"doi":"10.3847/2041-8213/ab0ec7","arxiv_id":"1906.11238","nct_id":null,"source_url":"https://doi.org/10.3847/2041-8213/ab0ec7","archive_url":"https://space-kitty.com/papers/arxiv:1906.11238","updated":"2019-06-26","pmid":null,"pmcid":null,"openalex_id":"W2936349953","pdf_url":"https://arxiv.org/pdf/1906.11238","abstract":"When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42+/-3 micro-as, which is circular and encompasses a central depression in brightness with a flux ratio ~10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5+/-0.7) x 10^9 Msun. Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:2311.08680","kind":"article","title":"First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way","authors":["Kazunori Akiyama","A. Alberdi","W. Alef","Juan Carlos Algaba","Richard Anantua","Keiichi Asada","Rebecca Azulay","U. Bach","Anne-Kathrin Baczko","David R. Ball","Mislav Baloković","John Barrett","Michi Bauböck","Bradford A. Benson","Dan Bintley","Lindy Blackburn","R. Blundell","Katherine L. Bouman","Geoffrey C. Bower","Hope Boyce","Michael Bremer","Christiaan D. Brinkerink","Roger Brissenden","S. Britzen","Avery E. Broderick"],"author_count":100,"year":2022,"published":"2022-05-01","venue":"The Astrophysical Journal Letters","cited_by":1865,"doi":"10.3847/2041-8213/ac6674","arxiv_id":"2311.08680","nct_id":null,"source_url":"https://doi.org/10.3847/2041-8213/ac6674","archive_url":"https://space-kitty.com/papers/arxiv:2311.08680","updated":"2023-11-16","pmid":null,"pmcid":null,"openalex_id":"W4280589633","pdf_url":"https://iopscience.iop.org/article/10.3847/2041-8213/ac6674/pdf","abstract":"We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A$^*$), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of $λ=1.3\\,{\\rm mm}$. The EHT data resolve a compact emission region with intrahour variability. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of $51.8 \\pm 2.3$\\,\\uas (68\\% credible interval). The ring has modest azimuthal brightness asymmetry and a comparatively dim interior. Using a large suite of numerical simulations, we demonstrate that the EHT images of Sgr A$^*$ are consistent with the expected appearance of a Kerr black hole with mass ${\\sim}4 \\times 10^6\\,{\\rm M}_\\odot$, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits as well as maser proper motion studies. Our model comparisons disfavor scenarios where the black hole is viewed at high inclination ($i > 50^\\circ$), as well as non-spinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way galaxy, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of $10^3-10^5$ gravitational radii to event horizon-scale images and variability. Furthermore, a comparison with the EHT results for the supermassive black hole M87$^*$ shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1906.11243","kind":"article","title":"First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole","authors":["The Event Horizon Telescope Collaboration"],"author_count":1,"year":2019,"published":"2019-06-26","venue":"ApJ, 875, L6, 2019 (April 10)","cited_by":1629,"doi":"10.3847/2041-8213/ab1141","arxiv_id":"1906.11243","nct_id":null,"source_url":"https://arxiv.org/abs/1906.11243","archive_url":"https://space-kitty.com/papers/arxiv:1906.11243","updated":"2019-06-26","pmid":null,"pmcid":null,"openalex_id":"W2936095933","pdf_url":"https://arxiv.org/pdf/1906.11243","abstract":"We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated from GRMHD models directly to the data. We compare the derived emission region and black hole parameters from these analyses with those recovered from reconstructed images. There is a remarkable consistency among all methods and data sets. We find that >50% of the total flux at arcsecond scales comes from near the horizon, and that the emission is dramatically suppressed interior to this region by a factor >10, providing direct evidence of the predicted shadow of a black hole. Across all methods, we measure a crescent diameter of 42+/-3 micro-as and constrain its fractional width to be <0.5. Associating the crescent feature with the emission surrounding the black hole shadow, we infer an angular gravitational radius of GM/Dc2 = 3.8+/- 0.4 micro-as. Folding in a distance measurement of 16.8(+0.8,-0.7) Mpc gives a black hole mass of M = 6.5 +/- 0.2(stat) +/-0.7(sys) 10^9 Msun. This measurement from lensed emission near the event horizon is consistent with the presence of a central Kerr black hole, as predicted by the general theory of relativity.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["astro-ph.GA","astro-ph.HE","gr-qc"],"details":null,"provenance":"arxiv+openalex","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1906.11241","kind":"article","title":"First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole","authors":["The Event Horizon Telescope Collaboration"],"author_count":1,"year":2019,"published":"2019-06-26","venue":"ApJ, 875, L4, 2019 (April 10)","cited_by":1501,"doi":"10.3847/2041-8213/ab0e85","arxiv_id":"1906.11241","nct_id":null,"source_url":"https://arxiv.org/abs/1906.11241","archive_url":"https://space-kitty.com/papers/arxiv:1906.11241","updated":"2019-06-26","pmid":null,"pmcid":null,"openalex_id":"W2937056002","pdf_url":"https://arxiv.org/pdf/1906.11241","abstract":"We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These images show a prominent ring with a diameter of ~40 micro-as, consistent with the size and shape of the lensed photon orbit encircling the \"shadow\" of a supermassive black hole. The ring is persistent across four observing nights and shows enhanced brightness in the south. To assess the reliability of these results, we implemented a two-stage imaging procedure. In the first stage, four teams, each blind to the others' work, produced images of M87 using both an established method (CLEAN) and a newer technique (regularized maximum likelihood). This stage allowed us to avoid shared human bias and to assess common features among independent reconstructions. In the second stage, we reconstructed synthetic data from a large survey of imaging parameters and then compared the results with the corresponding ground truth images. This stage allowed us to select parameters objectively to use when reconstructing images of M87. Across all tests in both stages, the ring diameter and asymmetry remained stable, insensitive to the choice of imaging technique. We describe the EHT imaging procedures, the primary image features in M87, and the dependence of these features on imaging assumptions.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["astro-ph.GA","astro-ph.IM","gr-qc"],"details":null,"provenance":"arxiv+openalex","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1906.11242","kind":"article","title":"First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring","authors":["The Event Horizon Telescope Collaboration"],"author_count":1,"year":2019,"published":"2019-06-26","venue":"ApJ, 875, L5, 2019 (April 10)","cited_by":1427,"doi":"10.3847/2041-8213/ab0f43","arxiv_id":"1906.11242","nct_id":null,"source_url":"https://arxiv.org/abs/1906.11242","archive_url":"https://space-kitty.com/papers/arxiv:1906.11242","updated":"2019-06-26","pmid":null,"pmcid":null,"openalex_id":"W2938000962","pdf_url":"https://arxiv.org/pdf/1906.11242","abstract":"The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87's large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["astro-ph.GA","astro-ph.HE","gr-qc"],"details":null,"provenance":"arxiv+openalex","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:2205.07787","kind":"article","title":"Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A ∗","authors":["Sunny Vagnozzi","Rittick Roy","Yu-Dai Tsai","Luca Visinelli","Misba Afrin","Alireza Allahyari","Parth Bambhaniya","Dipanjan Dey","Sushant G. Ghosh","Pankaj S. Joshi","Kimet Jusufi","Mohsen Khodadi","Rahul Kumar","Ali Övgün","Cosimo Bambi"],"author_count":15,"year":2023,"published":"2023-05-26","venue":"Classical and Quantum Gravity","cited_by":748,"doi":"10.1088/1361-6382/acd97b","arxiv_id":"2205.07787","nct_id":null,"source_url":"https://doi.org/10.1088/1361-6382/acd97b","archive_url":"https://space-kitty.com/papers/arxiv:2205.07787","updated":"2023-05-26","pmid":null,"pmcid":null,"openalex_id":"W4378373273","pdf_url":"https://iopscience.iop.org/article/10.1088/1361-6382/acd97b/pdf","abstract":"Horizon-scale images of black holes (BHs) and their shadows have opened an unprecedented window onto tests of gravity and fundamental physics in the strong-field regime. We consider a wide range of well-motivated deviations from classical General Relativity (GR) BH solutions, and constrain them using the Event Horizon Telescope (EHT) observations of Sagittarius A$^*$ (Sgr A$^*$), connecting the size of the bright ring of emission to that of the underlying BH shadow and exploiting high-precision measurements of Sgr A$^*$'s mass-to-distance ratio. The scenarios we consider, and whose fundamental parameters we constrain, include various regular BHs, string-inspired space-times, violations of the no-hair theorem driven by additional fields, alternative theories of gravity, novel fundamental physics frameworks, and BH mimickers including well-motivated wormhole and naked singularity space-times. We demonstrate that the EHT image of Sgr A$^*$ places particularly stringent constraints on models predicting a shadow size larger than that of a Schwarzschild BH of a given mass, with the resulting limits in some cases surpassing cosmological ones. Our results are among the first tests of fundamental physics from the shadow of Sgr A$^*$ and, while the latter appears to be in excellent agreement with the predictions of GR, we have shown that a number of well motivated alternative scenarios, including BH mimickers, are far from being ruled out at present.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:2311.09484","kind":"article","title":"First Sagittarius A* Event Horizon Telescope Results. VI. Testing the Black Hole Metric","authors":["Kazunori Akiyama","A. Alberdi","W. Alef","Juan Carlos Algaba","Richard Anantua","Keiichi Asada","Rebecca Azulay","U. Bach","Anne-Kathrin Baczko","David R. Ball","Mislav Baloković","John Barrett","Michi Bauböck","Bradford A. Benson","Dan Bintley","Lindy Blackburn","R. Blundell","Katherine L. Bouman","Geoffrey C. Bower","Hope Boyce","Michael Bremer","Christiaan D. Brinkerink","Roger Brissenden","S. Britzen","Avery E. Broderick"],"author_count":100,"year":2022,"published":"2022-05-12","venue":"The Astrophysical Journal Letters","cited_by":672,"doi":"10.3847/2041-8213/ac6756","arxiv_id":"2311.09484","nct_id":null,"source_url":"https://doi.org/10.3847/2041-8213/ac6756","archive_url":"https://space-kitty.com/papers/arxiv:2311.09484","updated":"2023-11-16","pmid":null,"pmcid":null,"openalex_id":"W4280631862","pdf_url":"https://iopscience.iop.org/article/10.3847/2041-8213/ac6756/pdf","abstract":"Astrophysical black holes are expected to be described by the Kerr metric. This is the only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein's equations and does not have pathologies outside of the event horizon. We present new constraints on potential deviations from the Kerr prediction based on 2017 EHT observations of Sagittarius A* (Sgr A*). We calibrate the relationship between the geometrically defined black hole shadow and the observed size of the ring-like images using a library that includes both Kerr and non-Kerr simulations. We use the exquisite prior constraints on the mass-to-distance ratio for Sgr A* to show that the observed image size is within $\\sim$ 10$\\%$ of the Kerr predictions. We use these bounds to constrain metrics that are parametrically different from Kerr as well as the charges of several known spacetimes. To consider alternatives to the presence of an event horizon we explore the possibility that Sgr A* is a compact object with a surface that either absorbs and thermally re-emits incident radiation or partially reflects it. Using the observed image size and the broadband spectrum of Sgr A*, we conclude that a thermal surface can be ruled out and a fully reflective one is unlikely. We compare our results to the broader landscape of gravitational tests. Together with the bounds found for stellar mass black holes and the M87 black hole, our observations provide further support that the external spacetimes of all black holes are described by the Kerr metric, independent of their mass.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1906.00873","kind":"article","title":"Black hole shadows, photon rings, and lensing rings","authors":["Samuel E. Gralla","DANIEL E. HOLZ","Robert M. Wald"],"author_count":3,"year":2019,"published":"2019-07-12","venue":"Physical review. D/Physical review. D.","cited_by":657,"doi":"10.1103/physrevd.100.024018","arxiv_id":"1906.00873","nct_id":null,"source_url":"https://doi.org/10.1103/physrevd.100.024018","archive_url":"https://space-kitty.com/papers/arxiv:1906.00873","updated":"2019-06-17","pmid":null,"pmcid":null,"openalex_id":"W2947118958","pdf_url":"https://arxiv.org/pdf/1906.00873","abstract":"The presence of a bright \"photon ring\" surrounding a dark \"black hole shadow\" has been discussed as an important feature of the observational appearance of emission originating near a black hole. We clarify the meaning and relevance of these heuristics with analytic calculations and numerical toy models. The standard usage of the term \"shadow\" describes the appearance of a black hole illuminated from all directions, including from behind the observer. A backlit black hole casts a somewhat larger shadow. Neither shadow heuristic is particularly relevant to understanding the appearance of emission originating near the black hole, where the emission profile and gravitational redshift play the dominant roles in determining the observed size of the central dark area. A photon ring results from light rays that orbit near the black hole before escaping to infinity, where they arrive near a ring-shaped \"critical curve\" on the image plane. Although the brightness can become arbitrarily large near this critical curve in the case of optically thin emitting matter, we show that the enhancement is only logarithmic, and hence is of no relevance to present observations. For optically thin emission from a geometrically thin or thick disk, photons that make only a fraction of an orbit will generically give rise to a much wider \"lensing ring,\" which is a demagnified image of the back of the disk, superimposed on top of the direct emission. The lensing ring is centered at a radius ~5% larger than the photon ring and its width is ~0.5-1M. It can be relatively brighter by a factor of 2-3 and thus could provide a significant feature in high resolution images. Nevertheless, the characteristic features of the observed image are dominated by the location and properties of the emitting matter near the black hole. We comment on the recent M87* Event Horizon Telescope observations and mass measurement.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:2311.09479","kind":"article","title":"First Sagittarius A* Event Horizon Telescope Results. III. Imaging of the Galactic Center Supermassive Black Hole","authors":["Kazunori Akiyama","A. Alberdi","W. Alef","Juan Carlos Algaba","Richard Anantua","Keiichi Asada","Rebecca Azulay","U. Bach","Anne-Kathrin Baczko","David R. Ball","Mislav Baloković","John Barrett","Michi Bauböck","Bradford A. Benson","Dan Bintley","Lindy Blackburn","R. Blundell","Katherine L. Bouman","Geoffrey C. Bower","Hope Boyce","Michael Bremer","Christiaan D. Brinkerink","Roger Brissenden","S. Britzen","Avery E. Broderick"],"author_count":100,"year":2022,"published":"2022-05-01","venue":"The Astrophysical Journal Letters","cited_by":449,"doi":"10.3847/2041-8213/ac6429","arxiv_id":"2311.09479","nct_id":null,"source_url":"https://doi.org/10.3847/2041-8213/ac6429","archive_url":"https://space-kitty.com/papers/arxiv:2311.09479","updated":"2023-11-16","pmid":null,"pmcid":null,"openalex_id":"W4280608520","pdf_url":"https://iopscience.iop.org/article/10.3847/2041-8213/ac6429/pdf","abstract":"We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with the Event Horizon Telescope in 2017 April at a wavelength of 1.3 mm. Imaging of Sgr A* has been conducted through surveys over a wide range of imaging assumptions using the classical CLEAN algorithm, regularized maximum likelihood methods, and a Bayesian posterior sampling method. Different prescriptions have been used to account for scattering effects by the interstellar medium towards the Galactic Center. Mitigation of the rapid intra-day variability that characterizes Sgr A* has been carried out through the addition of a \"variability noise budget\" in the observed visibilities, facilitating the reconstruction of static full-track images. Our static reconstructions of Sgr A* can be clustered into four representative morphologies that correspond to ring images with three different azimuthal brightness distributions, and a small cluster that contains diverse non-ring morphologies. Based on our extensive analysis of the effects of sparse $(u,v)$-coverage, source variability and interstellar scattering, as well as studies of simulated visibility data, we conclude that the Event Horizon Telescope Sgr A* data show compelling evidence for an image that is dominated by a bright ring of emission with a ring diameter of $\\sim$ 50 $μ$as, consistent with the expected \"shadow\" of a $4\\times10^6 M_\\odot$ black hole in the Galactic Center located at a distance of 8 kpc.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1509.00021","kind":"article","title":"Shadows of Kerr Black Holes with Scalar Hair","authors":["Pedro V. P. Cunha","Carlos Herdeiro","Eugen Radu","Helgi Freyr Rúnarsson"],"author_count":4,"year":2015,"published":"2015-11-16","venue":"Physical Review Letters","cited_by":530,"doi":"10.1103/physrevlett.115.211102","arxiv_id":"1509.00021","nct_id":null,"source_url":"https://doi.org/10.1103/physrevlett.115.211102","archive_url":"https://space-kitty.com/papers/arxiv:1509.00021","updated":"2015-11-07","pmid":"26636837","pmcid":null,"openalex_id":"W1891608179","pdf_url":"http://link.aps.org/pdf/10.1103/PhysRevLett.115.211102","abstract":"Using backwards ray tracing, we study the shadows of Kerr black holes with scalar hair (KBHsSH). KBHsSH interpolate continuously between Kerr BHs and boson stars (BSs), so we start by investigating the lensing of light due to BSs. Moving from the weak to the strong gravity region, BSs - which by themselves have no shadows - are classified, according to the lensing produced, as: $(i)$ non-compact, which yield no multiple images; $(ii)$ compact, which produce an increasing number of Einstein rings and multiple images of the whole celestial sphere; $(iii)$ ultra-compact, which possess light rings, yielding an infinite number of images with (we conjecture) a self-similar structure. The shadows of KBHsSH, for Kerr-like horizons and non-compact BS-like hair, are analogous to, but distinguishable from, those of comparable Kerr BHs. But for non-Kerr-like horizons and ultra-compact BS-like hair, the shadows of KBHsSH are drastically different: novel shapes arise, sizes are considerably smaller and multiple shadows of a single BH become possible. Thus, KBHsSH provide quantitatively and qualitatively new templates for ongoing (and future) very large baseline interferometry (VLBI) observations of BH shadows, such as those of the Event Horizon Telescope.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1907.04329","kind":"article","title":"Universal interferometric signatures of a black hole’s photon ring","authors":["Michael D. Johnson","Alexandru Lupsasca","Andrew Strominger","George N. Wong","Shahar Hadar","Daniel Kapec","Ramesh Narayan","Andrew Chael","Charles F. Gammie","Peter Louis Galison","Daniel C. M. Palumbo","Sheperd S. Doeleman","Lindy Blackburn","Maciek Wielgus","Dominic W. Pesce","Joseph R. Farah","James M. Moran"],"author_count":17,"year":2020,"published":"2020-03-18","venue":"Science Advances","cited_by":410,"doi":"10.1126/sciadv.aaz1310","arxiv_id":"1907.04329","nct_id":null,"source_url":"https://doi.org/10.1126/sciadv.aaz1310","archive_url":"https://space-kitty.com/papers/arxiv:1907.04329","updated":"2020-03-27","pmid":"32206723","pmcid":null,"openalex_id":"W2961953245","pdf_url":"https://arxiv.org/pdf/1907.04329","abstract":"The Event Horizon Telescope image of the supermassive black hole in the galaxy M87 is dominated by a bright, unresolved ring. General relativity predicts that embedded within this image lies a thin \"photon ring,\" which is composed of an infinite sequence of self-similar subrings that are indexed by the number of photon orbits around the black hole. The subrings approach the edge of the black hole \"shadow,\" becoming exponentially narrower but weaker with increasing orbit number, with seemingly negligible contributions from high order subrings. Here, we show that these subrings produce strong and universal signatures on long interferometric baselines. These signatures offer the possibility of precise measurements of black hole mass and spin, as well as tests of general relativity, using only a sparse interferometric array.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by-nc","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:2105.09343","kind":"article","title":"Constraints on black-hole charges with the 2017 EHT observations of M87*","authors":["Prashant Kocherlakota","Luciano Rezzolla","Heino D. Falcke","Christian M. Fromm","M. Krämer","Yosuke Mizuno","Antonios Nathanail","Héctor Olivares","Ziri Younsi","Kazunori Akiyama","A. Alberdi","W. Alef","Juan Carlos Algaba","Richard Anantua","Keiichi Asada","Rebecca Azulay","Anne-Kathrin Baczko","David R. Ball","Mislav Baloković","John Barrett","Bradford A. Benson","Dan Bintley","Lindy Blackburn","R. Blundell","W. Boland"],"author_count":100,"year":2021,"published":"2021-05-20","venue":"Physical review. D/Physical review. D.","cited_by":344,"doi":"10.1103/physrevd.103.104047","arxiv_id":"2105.09343","nct_id":null,"source_url":"https://doi.org/10.1103/physrevd.103.104047","archive_url":"https://space-kitty.com/papers/arxiv:2105.09343","updated":"2021-05-19","pmid":null,"pmcid":null,"openalex_id":"W3161957533","pdf_url":"http://link.aps.org/pdf/10.1103/PhysRevD.103.104047","abstract":"Our understanding of strong gravity near supermassive compact objects has recently improved thanks to the measurements made by the Event Horizon Telescope (EHT). We use here the M87* shadow size to infer constraints on the physical charges of a large variety of nonrotating or rotating black holes. For example, we show that the quality of the measurements is already sufficient to rule out that M87* is a highly charged dilaton black hole. Similarly, when considering black holes with two physical and independent charges, we are able to exclude considerable regions of the space of parameters for the doubly-charged dilaton and the Sen black holes.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Black Holes and Theoretical Physics"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1905.12421","kind":"article","title":"Hunting for extra dimensions in the shadow of M87*","authors":["Sunny Vagnozzi","Luca Visinelli"],"author_count":2,"year":2019,"published":"2019-07-12","venue":"Physical review. D/Physical review. D.","cited_by":364,"doi":"10.1103/physrevd.100.024020","arxiv_id":"1905.12421","nct_id":null,"source_url":"https://doi.org/10.1103/physrevd.100.024020","archive_url":"https://space-kitty.com/papers/arxiv:1905.12421","updated":"2019-07-12","pmid":null,"pmcid":null,"openalex_id":"W2960227302","pdf_url":"https://arxiv.org/pdf/1905.12421","abstract":"The Event Horizon Telescope has recently provided the first image of the dark shadow around the supermassive black hole M87*. The observation of a highly circular shadow provides strong limits on deviations of M87*'s quadrupole moment from the Kerr value. We show that the absence of such a deviation can be used to constrain the physics of extra dimensions of spacetime. Focusing on the Randall-Sundrum AdS$_5$ brane-world scenario, we show that the observation of M87*'s dark shadow sets the limit $\\ell \\lesssim 170\\,{\\rm AU}$, where $\\ell$ is the AdS$_5$ curvature radius. This limit is among the first quantitative constraints on exotic physics obtained from the extraordinary first ever image of the dark shadow of a black hole.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Black Holes and Theoretical Physics"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1912.08231","kind":"article","title":"Magnetically charged black holes from non-linear electrodynamics and the Event Horizon Telescope","authors":["Alireza Allahyari","Mohsen Khodadi","Sunny Vagnozzi","David F. Mota"],"author_count":4,"year":2020,"published":"2020-02-04","venue":"Journal of Cosmology and Astroparticle Physics","cited_by":337,"doi":"10.1088/1475-7516/2020/02/003","arxiv_id":"1912.08231","nct_id":null,"source_url":"https://doi.org/10.1088/1475-7516/2020/02/003","archive_url":"https://space-kitty.com/papers/arxiv:1912.08231","updated":"2020-01-20","pmid":null,"pmcid":null,"openalex_id":"W2996263232","pdf_url":"https://arxiv.org/pdf/1912.08231","abstract":"Non-linear electrodynamics (NLED) theories are well-motivated extensions of QED in the strong field regime, and have long been studied in the search for regular black hole (BH) solutions. We consider two well-studied and well-motivated NLED models coupled to General Relativity: the Euler-Heisenberg model and the Bronnikov model. After carefully accounting for the effective geometry induced by the NLED corrections, we determine the shadows of BHs within these two models. We then compare these to the shadow of the supermassive BH M87* recently imaged by the Event Horizon Telescope collaboration. In doing so, we are able to extract upper limits on the black hole magnetic charge, thus providing novel constraints on fundamental physics from this new extraordinary probe.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Black Holes and Theoretical Physics"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:2010.01055","kind":"article","title":"Gravitational Test Beyond the First Post-Newtonian Order with the Shadow of the M87 Black Hole","authors":["Dimitrios Psaltis","Lia Medeiros","Pierre Christian","Feryal Ozel","Kazunori Akiyama","Antxon Alberdi","Walter Alef","Keiichi Asada","Rebecca Azulay","David Ball","Mislav Balokovic","John Barrett","Dan Bintley","Lindy Blackburn","Wilfred Boland","Geoffrey C. Bower","Michael Bremer","Christiaan D. Brinkerink","Roger Brissenden","Silke Britzen","Dominique Broguiere","Thomas Bronzwaer","Do-Young Byun","John E. Carlstrom","Andrew Chael"],"author_count":188,"year":2020,"published":"2020-10-02","venue":"Physical Review Letters","cited_by":336,"doi":"10.1103/physrevlett.125.141104","arxiv_id":"2010.01055","nct_id":null,"source_url":"https://arxiv.org/abs/2010.01055","archive_url":"https://space-kitty.com/papers/arxiv:2010.01055","updated":"2020-10-02","pmid":"33064506","pmcid":null,"openalex_id":"W3091374297","pdf_url":"https://arxiv.org/pdf/2010.01055","abstract":"The 2017 Event Horizon Telescope (EHT) observations of the central source in M87 have led to the first measurement of the size of a black-hole shadow. This observation offers a new and clean gravitational test of the black-hole metric in the strong-field regime. We show analytically that spacetimes that deviate from the Kerr metric but satisfy weak-field tests can lead to large deviations in the predicted black-hole shadows that are inconsistent with even the current EHT measurements. We use numerical calculations of regular, parametric, non-Kerr metrics to identify the common characteristic among these different parametrizations that control the predicted shadow size. We show that the shadow-size measurements place significant constraints on deviation parameters that control the second post-Newtonian and higher orders of each metric and are, therefore, inaccessible to weak-field tests. The new constraints are complementary to those imposed by observations of gravitational waves from stellar-mass sources.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["gr-qc","astro-ph.HE"],"details":null,"provenance":"arxiv+openalex","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1607.05767","kind":"article","title":"New method for shadow calculations: Application to parametrized axisymmetric black holes","authors":["Ziri Younsi","A. Zhidenko","Luciano Rezzolla","R. A. Konoplya","Yosuke Mizuno"],"author_count":5,"year":2016,"published":"2016-10-18","venue":"Physical review. D/Physical review. D.","cited_by":337,"doi":"10.1103/physrevd.94.084025","arxiv_id":"1607.05767","nct_id":null,"source_url":"https://doi.org/10.1103/physrevd.94.084025","archive_url":"https://space-kitty.com/papers/arxiv:1607.05767","updated":"2016-10-15","pmid":null,"pmcid":null,"openalex_id":"W2479388119","pdf_url":"https://arxiv.org/pdf/1607.05767","abstract":"Collaborative international efforts under the name of the Event Horizon Telescope project, using sub- mm very long baseline interferometry, are soon expected to provide the first images of the shadow cast by the candidate supermassive black hole in our Galactic center, Sagittarius A*. Observations of this shadow would provide direct evidence of the existence of astrophysical black holes. Although it is expected that astrophysical black holes are described by the axisymmetric Kerr solution, there also exist many other black hole solutions, both in general relativity and in other theories of gravity, which cannot presently be ruled out. To this end, we present calculations of black hole shadow images from various metric theories of gravity as described by our recent work on a general parameterisation of axisymmetric black holes [R. Konoplya, L. Rezzolla and A. Zhidenko, Phys. Rev. D 93, 064015 (2016)]. An algorithm to perform general ray-tracing calculations for any metric theory of gravity is first outlined and then employed to demonstrate that even for extremal metric deformation parameters of various black hole spacetimes, this parameterisation is both robust and rapidly convergent to the correct solution.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:2005.05992","kind":"article","title":"Black holes with scalar hair in light of the Event Horizon Telescope","authors":["Mohsen Khodadi","Alireza Allahyari","Sunny Vagnozzi","David F. Mota"],"author_count":4,"year":2020,"published":"2020-09-14","venue":"Journal of Cosmology and Astroparticle Physics","cited_by":288,"doi":"10.1088/1475-7516/2020/09/026","arxiv_id":"2005.05992","nct_id":null,"source_url":"https://doi.org/10.1088/1475-7516/2020/09/026","archive_url":"https://space-kitty.com/papers/arxiv:2005.05992","updated":"2020-08-09","pmid":null,"pmcid":null,"openalex_id":"W3024992577","pdf_url":"https://arxiv.org/pdf/2005.05992","abstract":"Searching for violations of the no-hair theorem (NHT) is a powerful way to test gravity, and more generally fundamental physics, particularly with regards to the existence of additional scalar fields. The first observation of a black hole (BH) shadow by the Event Horizon Telescope (EHT) has opened a new direct window onto tests of gravity in the strong-field regime, including probes of violations of the NHT. We consider two scenarios described by the Einstein-Maxwell equations of General Relativity and electromagnetism, to which we add a scalar field. In the first case we consider a minimally-coupled scalar field with a potential, whereas in the second case the field is conformally-coupled to curvature. In both scenarios we construct charged BH solutions, which are found to carry primary scalar hair. We then compute the shadows cast by these two BHs as a function of their electric charge and scalar hair parameter. Comparing these shadows to the shadow of M87* recently imaged by the EHT collaboration, we set constraints on the amount of scalar hair carried by these two BHs. The conformally-coupled case admits a regime for the hair parameter, compatible with EHT constraints, describing a so-called mutated Reissner-Nordström BH: this solution was recently found to effectively mimic a wormhole. Our work provides novel constraints on fundamental physics, and in particular on violations of the no-hair theorem and the existence of additional scalar fields, from the shadow of M87*.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Black Holes and Theoretical Physics"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1702.07361","kind":"article","title":"Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope using Sparse Modeling","authors":["Kazunori Akiyama","Kazuki Kuramochi","Shiro Ikeda","Vincent L. Fish","Fumie Tazaki","Mareki Honma","Sheperd S. Doeleman","Avery Broderick","Jason Dexter","Monika Mościbrodzka","Katherine L. Bouman","Andrew Chael","Masamichi Zaizen"],"author_count":13,"year":2017,"published":"2017-02-23","venue":"The Astrophysical Journal","cited_by":174,"doi":"10.3847/1538-4357/aa6305","arxiv_id":"1702.07361","nct_id":null,"source_url":"https://arxiv.org/abs/1702.07361","archive_url":"https://space-kitty.com/papers/arxiv:1702.07361","updated":"2017-02-23","pmid":null,"pmcid":null,"openalex_id":"W2594279543","pdf_url":"https://arxiv.org/pdf/1702.07361","abstract":"We propose a new imaging technique for radio and optical/infrared interferometry. The proposed technique reconstructs the image from the visibility amplitude and closure phase, which are standard data products of short-millimeter very long baseline interferometers such as the Event Horizon Telescope (EHT) and optical/infrared interferometers, by utilizing two regularization functions: the $\\ell_1$-norm and total variation (TV) of the brightness distribution. In the proposed method, optimal regularization parameters, which represent the sparseness and effective spatial resolution of the image, are derived from data themselves using cross validation (CV). As an application of this technique, we present simulated observations of M87 with the EHT based on four physically motivated models. We confirm that $\\ell_1$+TV regularization can achieve an optimal resolution of $\\sim 20-30$% of the diffraction limit $λ/D_{\\rm max}$, which is the nominal spatial resolution of a radio interferometer. With the proposed technique, the EHT can robustly and reasonably achieve super-resolution sufficient to clearly resolve the black hole shadow. These results make it promising for the EHT to provide an unprecedented view of the event-horizon-scale structure in the vicinity of the super-massive black hole in M87 and also the Galactic center Sgr A*.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["astro-ph.IM","astro-ph.HE"],"details":null,"provenance":"arxiv+openalex","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1411.1454","kind":"article","title":"A General Relativistic Null Hypothesis Test with Event Horizon Telescope Observations of the black-hole shadow in Sgr A*","authors":["Dimitrios Psaltis","Feryal Ozel","Chi-Kwan Chan","Daniel P. Marrone"],"author_count":4,"year":2014,"published":"2014-11-06","venue":"The Astrophysical Journal","cited_by":131,"doi":"10.1088/0004-637x/814/2/115","arxiv_id":"1411.1454","nct_id":null,"source_url":"https://arxiv.org/abs/1411.1454","archive_url":"https://space-kitty.com/papers/arxiv:1411.1454","updated":"2015-11-10","pmid":null,"pmcid":null,"openalex_id":"W2165244905","pdf_url":"https://arxiv.org/pdf/1411.1454","abstract":"The half opening angle of a Kerr black-hole shadow is always equal to (5+-0.2)GM/Dc^2, where M is the mass of the black hole and D is its distance from the Earth. Therefore, measuring the size of a shadow and verifying whether it is within this 4% range constitutes a null hypothesis test of General Relativity. We show that the black hole in the center of the Milky Way, Sgr A*, is the optimal target for performing this test with upcoming observations using the Event Horizon Telescope. We use the results of optical/IR monitoring of stellar orbits to show that the mass-to-distance ratio for Sgr A* is already known to an accuracy of +-4%. We investigate our prior knowledge of the properties of the scattering screen between Sgr A and the Earth, the effects of which will need to be corrected for in order for the black-hole shadow to appear sharp against the background emission. Finally, we explore an edge detection scheme for interferometric data and a pattern matching algorithm based on the Hough/Radon transform and demonstrate that the shadow of the black hole at 1.3 mm can be localized, in principle, to within ~9%. All these results suggest that our prior knowledge of the properties of the black hole, of scattering broadening, and of the accretion flow can only limit this General Relativistic null hypothesis test with Event Horizon Telescope observations of Sgr A* to 10%.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["astro-ph.HE"],"details":null,"provenance":"arxiv+openalex","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1804.05812","kind":"article","title":"The current ability to test theories of gravity with black hole shadows","authors":["Yosuke Mizuno","Ziri Younsi","Christian M. Fromm","Oliver Porth","Mariafelicia De Laurentis","Hector Olivares","Heino Falcke","M. Krämer","Luciano Rezzolla"],"author_count":9,"year":2018,"published":"2018-04-13","venue":"Nature Astronomy","cited_by":293,"doi":"10.1038/s41550-018-0449-5","arxiv_id":"1804.05812","nct_id":null,"source_url":"https://doi.org/10.1038/s41550-018-0449-5","archive_url":"https://space-kitty.com/papers/arxiv:1804.05812","updated":"2018-04-16","pmid":null,"pmcid":null,"openalex_id":"W2797653139","pdf_url":"https://arxiv.org/pdf/1804.05812","abstract":"Our Galactic Center, Sagittarius A* (Sgr A*), is believed to harbour a supermassive black hole (BH), as suggested by observations tracking individual orbiting stars. Upcoming sub-millimetre very-long-baseline-interferometry (VLBI) images of Sgr A* carried out by the Event-Horizon-Telescope Collaboration (EHTC) are expected to provide critical evidence for the existence of this supermassive BH. We assess our present ability to use EHTC images to determine if they correspond to a Kerr BH as predicted by Einstein's theory of general relativity (GR) or to a BH in alternative theories of gravity. To this end, we perform general-relativistic magnetohydrodynamical (GRMHD) simulations and use general-relativistic radiative transfer (GRRT) calculations to generate synthetic shadow images of a magnetised accretion flow onto a Kerr BH. In addition, and for the first time, we perform GRMHD simulations and GRRT calculations for a dilaton BH, which we take as a representative solution of an alternative theory of gravity. Adopting the VLBI configuration from the 2017 EHTC campaign, we find that it could be extremely difficult to distinguish between BHs from different theories of gravity, thus highlighting that great caution is needed when interpreting BH images as tests of GR.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1404.7095","kind":"article","title":"Imaging the Supermassive Black Hole Shadow and Jet Base of M87 with the Event Horizon Telescope","authors":["Ru-Sen Lu","Avery E. Broderick","Fabien Baron","John D. Monnier","Vincent L. Fish","Sheperd S. Doeleman","Victor Pankratius"],"author_count":7,"year":2014,"published":"2014-04-28","venue":"The Astrophysical Journal","cited_by":110,"doi":"10.1088/0004-637x/788/2/120","arxiv_id":"1404.7095","nct_id":null,"source_url":"https://arxiv.org/abs/1404.7095","archive_url":"https://space-kitty.com/papers/arxiv:1404.7095","updated":"2014-04-28","pmid":null,"pmcid":null,"openalex_id":"W2113799640","pdf_url":"https://arxiv.org/pdf/1404.7095","abstract":"The Event Horizon Telescope (EHT) is a project to assemble a Very Long Baseline Interferometry (VLBI) network of mm wavelength dishes that can resolve strong field General Relativistic signatures near a supermassive black hole. As planned, the EHT will include enough dishes to enable imaging of the predicted black hole \"shadow\", a feature caused by severe light bending at the black hole boundary. The center of M87, a giant elliptical galaxy, presents one of the most interesting EHT targets as it exhibits a relativistic jet, offering the additional possibility of studying jet genesis on Schwarzschild radius scales. Fully relativistic models of the M87 jet that fit all existing observational constraints now allow horizon-scale images to be generated. We perform realistic VLBI simulations of M87 model images to examine detectability of the black shadow with the EHT, focusing on a sequence of model images with a changing jet mass load radius. When the jet is launched close to the black hole, the shadow is clearly visible both at 230 and 345 GHz. The EHT array with a resolution of 20-30$μ$as resolution ($\\sim$2-4 Schwarzschild radii) is able to image this feature independent of any theoretical models and we show that imaging methods used to process data from optical interferometers are applicable and effective for EHT data sets. We demonstrate that the EHT is also capable of tracing real-time structural changes on a few Schwarzschild radii scales, such as those implicated by VHE flaring activity of M87. While inclusion of ALMA in the EHT is critical for shadow imaging, generally the array is robust against loss of a station.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["astro-ph.IM","astro-ph.HE"],"details":null,"provenance":"arxiv+openalex","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1910.02957","kind":"article","title":"The Shadow of a Spherically Accreting Black Hole","authors":["Ramesh Narayan","Michael D. Johnson","Charles F. Gammie"],"author_count":3,"year":2019,"published":"2019-11-06","venue":"The Astrophysical Journal Letters","cited_by":248,"doi":"10.3847/2041-8213/ab518c","arxiv_id":"1910.02957","nct_id":null,"source_url":"https://doi.org/10.3847/2041-8213/ab518c","archive_url":"https://space-kitty.com/papers/arxiv:1910.02957","updated":"2019-10-25","pmid":null,"pmcid":null,"openalex_id":"W2979557788","pdf_url":"https://iopscience.iop.org/article/10.3847/2041-8213/ab518c/pdf","abstract":"We explore a simple spherical model of optically thin accretion on a Schwarzschild black hole, and study the properties of the image as seen by a distant observer. We show that a dark circular region in the center --- a shadow --- is always present. The outer edge of the shadow is located at the photon ring radius $b_{\\rm ph} \\equiv \\sqrt{27}r_g$, where $r_g=GM/c^2$ is the gravitational radius of the accreting mass $M$. The location of the shadow edge is independent of the inner radius at which the accreting gas stops radiating. The size of the observed shadow is thus a signature of the spacetime geometry and it is hardly influenced by accretion details. We briefly discuss the relevance of these results for the Event Horizon Telescope image of the supermassive black hole in M87.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:2012.05186","kind":"article","title":"Einstein-Æther Gravity in the light of Event Horizon Telescope Observations of M87*","authors":["Mohsen Khodadi","Emmanuel N. Saridakis"],"author_count":2,"year":2020,"published":"2020-12-09","venue":"Phys.Dark Univ. 32 (2021) 100835","cited_by":88,"doi":"10.1016/j.dark.2021.100835","arxiv_id":"2012.05186","nct_id":null,"source_url":"https://arxiv.org/abs/2012.05186","archive_url":"https://space-kitty.com/papers/arxiv:2012.05186","updated":"2021-05-11","pmid":null,"pmcid":null,"openalex_id":"W3161393298","pdf_url":"https://arxiv.org/pdf/2012.05186","abstract":"We investigate Einstein-Æther gravity in light of the recent Event Horizon Telescope (EHT) observations of the M87*. The shape and size of the observed black hole shadow contains information of the geometry in its vicinity, and thus one can consider it as a potential probe to investigate different gravitational theories, since the involved calculation framework is enriched with different size-rotation features as well as with extra model parameters. In the case of Einstein-Æther gravity the black hole solutions include two classes depending on the involved æther parameters. We calculate the corresponding photon effective potential, the unstable photon sphere radius, and finally, the induced angular size, which combined with the mass and the distance can lead to a single prediction that quantifies the black hole shadow, namely the diameter per unit mass $d$. Since $d_{M87*}$ is observationally known from the EHT Probe, we extract the corresponding parameter regions in order to obtain consistency. We find that Einstein-Æther black hole solutions agree with the shadow size of EHT M87*, if the involved Æther parameters are restricted within specific ranges, along with an upper bound on the dimensionless spin parameter $a$, which is verified by a full scan of the parameter space within $1σ$-error.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["gr-qc","hep-th"],"details":null,"provenance":"arxiv+openalex","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:1811.01260","kind":"article","title":"Black Hole Parameter Estimation from Its Shadow","authors":["Rahul Kumar","Sushant G. Ghosh"],"author_count":2,"year":2020,"published":"2020-03-31","venue":"The Astrophysical Journal","cited_by":224,"doi":"10.3847/1538-4357/ab77b0","arxiv_id":"1811.01260","nct_id":null,"source_url":"https://doi.org/10.3847/1538-4357/ab77b0","archive_url":"https://space-kitty.com/papers/arxiv:1811.01260","updated":"2020-05-10","pmid":null,"pmcid":null,"openalex_id":"W2898934423","pdf_url":"https://iopscience.iop.org/article/10.3847/1538-4357/ab77b0/pdf","abstract":"The Event Horizon Telescope (EHT), a global submillimeter wavelength very long baseline interferometry array, unveiled event-horizon-scale images of the supermassive black hole M87* as an asymmetric bright emission ring with a diameter of $ 42 \\pm 3\\; μ$as, and it is consistent with the shadow of a Kerr black hole of general relativity. A Kerr black hole is also a solution of some alternative theories of gravity, while several modified theories of gravity admit non-Kerr black holes. While earlier estimates for the M87* black hole mass, depending on the method used, fall in the range $ \\approx 3\\times 10^9 M_\\odot- 7 \\times 10^9 $$ M_\\odot $, the EHT data indicated a mass for the M87* black hole of $(6.5 \\pm 0.7) \\times 10^9 M_\\odot $. This offers another promising tool to estimate black hole parameters and to probe theories of gravity in its most extreme region near the event horizon. The important question arises: Is it possible by a simple technique to estimate black hole parameters from its shadow, for arbitrary models? In this paper, we present observables, expressed in terms of ordinary integrals, characterizing a haphazard shadow shape to estimate the parameters associated with black holes, and then illustrate its relevance to four different models: Kerr, Kerr$-$Newman, and two rotating regular models. Our method is robust, accurate, and consistent with the results obtained from existing formalism, and it is applicable to more general shadow shapes that may not be circular due to noisy data.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."},{"id":"arxiv:2103.11417","kind":"article","title":"Parameter estimation of hairy Kerr black holes from its shadow and constraints from M87*","authors":["Misba Afrin","Rahul Kumar","Sushant G. Ghosh"],"author_count":3,"year":2021,"published":"2021-04-30","venue":"Monthly Notices of the Royal Astronomical Society","cited_by":202,"doi":"10.1093/mnras/stab1260","arxiv_id":"2103.11417","nct_id":null,"source_url":"https://doi.org/10.1093/mnras/stab1260","archive_url":"https://space-kitty.com/papers/arxiv:2103.11417","updated":"2021-05-31","pmid":null,"pmcid":null,"openalex_id":"W3139181125","pdf_url":"https://arxiv.org/pdf/2103.11417","abstract":"The recently obtained hairy Kerr black holes, due to additional sources or surrounding fluid, like dark matter, with conserved energy-momentum tensor, have a deviation $α$ and primary hair $l_0$, apart from rotation parameter $a$ and mass $M$. In the wake of the \\textit{Event Horizon Telescope} (\\textit{EHT}) observations of the supermassive black hole M87*, a recent surge in interest in black hole shadows suggests comparing the black holes in general relativity (GR) and modified theories of gravity (MoG) to assess these models' differences. Motivated by this, we take on an extensive study of the rotating hairy Kerr black holes, which encompasses, in particular cases, the Kerr black hole ($α=0$). We investigate ergosphere and shadows of the black holes to infer that their size and shape are affected due to the $l_0$ and are found to harbour a richer chaotic structure. In particular, the hairy Kerr black holes possess smaller size but more distorted shadows when compared with Kerr black holes. We also estimate the parameters $l_0$ and $a$ associated with hairy Kerr black holes using the shadow observables. The inferred circularity deviation $ΔC \\leq 0.1$ for the M87* black hole is satisfied, whereas shadow angular diameter $θ_{d}=42 \\pm 3 μas$, within $1 σ$ region, for a given choice of $α$, places bounds on the parameters $a$ and $l_0$. Interestingly, the shadow axial ratio obeying $1< D_x \\lesssim 4/3$ is in agreement with the \\textit{EHT} results and thus eventuates in the hairy Kerr black holes being suitable candidates for astrophysical black holes.","abstract_license":"CC0-1.0 (arXiv descriptive metadata)","license":null,"is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Astrophysical Phenomena and Observations"],"details":null,"provenance":"openalex+arxiv","attribution":"Abstract: arXiv descriptive metadata (CC0). Thank you to arXiv for use of its open access interoperability. This service was not reviewed or approved by, nor does it necessarily express or reflect the policies or opinions of, arXiv."}],"next":"https://space-kitty.com/api/v1/topics/black-hole-physics/papers?sort=top&limit=25&offset=25"}