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Article
Astronomy & Astrophysics
Maria J. Rioja et al.
Summary: MM VLBI observations are hindered by limited sensitivity caused by fast tropospheric fluctuations. Applying next-generation frequency phase transfer calibration techniques and simultaneous multi-frequency observations on the ngEHT can bring significant benefits. Simulation studies show that including the 85 GHz band has a transformational impact on the ngEHT array capabilities, greatly improving sensitivity and enabling a wide range of scientific inquiries. We propose a solution for scatter-broadened sources like SgrA* and recommend the inclusion of the 85 GHz band in the ngEHT's receiver design.
Article
Astronomy & Astrophysics
Freek Roelofs et al.
Summary: The ngEHT is an enhanced version of the EHT array, with new antennas and upgrades of existing antennas. It provides opportunities for new scientific exploration due to increased uv-coverage, sensitivity, and frequency coverage. The ngEHT Analysis Challenges involve generating synthetic datasets and evaluating analysis results to improve algorithms and analysis strategies.
Article
Astronomy & Astrophysics
Michael D. Johnson et al.
Summary: The Event Horizon Telescope (EHT) has produced the first images of supermassive black holes in the M87 galaxy and the Milky Way. The next-generation EHT (ngEHT) program aims to enhance the resolution, dynamic range, and temporal coverage of these observations, enabling groundbreaking discoveries in black hole science. The ngEHT and its instrument requirements have been formulated through a collaborative international effort involving hundreds of scientists.
Article
Astronomy & Astrophysics
Avery E. Broderick et al.
Summary: The direct detection of a bright, ring-like structure in horizon-resolving images of M87* by the Event Horizon Telescope (EHT) validates general relativity. By observing multiple rings, researchers can break degeneracy and measure the mass and spin of the black hole independently. These findings provide valuable tests for general relativity.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Kazunori Akiyama et al.
Summary: This study presents new constraints on potential deviations from the Kerr metric based on observations of Sagittarius A* (Sgr A*) using the 2017 Event Horizon Telescope. The authors calibrate the relationship between the black hole shadow and the observed size of ring-like images using both Kerr and non-Kerr simulations. They conclude that the observed image size is within similar to 10% of the Kerr predictions and use these bounds to constrain alternative metrics and charges of spacetimes. The study also explores the possibility of Sgr A* being a compact object with a thermal or reflective surface and compares the results to other gravitational tests.
ASTROPHYSICAL JOURNAL LETTERS
(2022)
Article
Astronomy & Astrophysics
Kazunori Akiyama et al.
Summary: This study presents the first observations of Sagittarius A* using the Event Horizon Telescope. The data supports the presence of a supermassive black hole at the center of the Milky Way, with an image that is consistent with the expected appearance of a Kerr black hole. The results also connect dynamical measurements of stellar orbits to event-horizon-scale images.
ASTROPHYSICAL JOURNAL LETTERS
(2022)
Article
Engineering, Aerospace
Leonid Gurvits et al.
Summary: Ultra-high angular resolution plays a crucial role in making fundamental discoveries in astronomy. Recent advancements in millimeter VLBI system and Space VLBI mission have achieved a high level of angular resolution. The need for further development towards microarcsecond-level resolution can only be met by placing interferometric systems in space. This paper presents a concept and science objectives for a space-based millimeter/submillimeter interferometric system and discusses technological challenges and possible solutions.
Article
Astronomy & Astrophysics
Lei Liu et al.
Summary: OmniUV is a versatile simulation toolkit for space and ground VLBI observations, supporting various types of stations and functionalities such as trajectory calculation, baseline uv calculation, visibility simulation, and image reconstruction.
ASTRONOMICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
H. Paugnat et al.
Summary: This study aims to understand how the photon rings of a Kerr black hole vary with its surrounding emission. Images of thin equatorial disks accreting onto a Kerr black hole are simulated using the ray tracing code Gyoto, and the shape of the resulting photon rings is extracted from their interferometric signatures. The analysis is repeated for hundreds of models with different emission profiles, black hole spins, and observer inclinations.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
F. H. Vincent et al.
Summary: This study aims to explore various accretion flows onto supermassive black hole M 87* by developing an analytical model and numerically integrating the radiative transfer equation in Kerr spacetime. The results show that the n = 2 photon ring at 345 GHz displays clear signatures in both the image and visibility domains, indicating promising future space-VLBI measurements.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
F. H. Vincent et al.
Summary: Researchers aim to develop a simple analytic disk model for the accretion flow of M87* to predict its image, assuming it is a Kerr black hole or an alternative compact object. They computed synchrotron emission from the disk model and carried out numerical fits to the EHT data, showing that alternatives to the Kerr spacetime may provide similar results and further observations are needed to test the Kerr paradigm conclusively.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Leonid I. Gurvits et al.
Summary: THEZA is a concept proposed in the ESA Voyage 2050 White Paper for ultra-sharp imaging of celestial radio sources, focusing on physics of spacetime near supermassive black holes. It aims to provide researchers with orders of magnitude improvements in resolution and dynamic range for direct imaging studies, opening up a range of previously unreachable parameters of observational astrophysics.
EXPERIMENTAL ASTRONOMY
(2021)
Article
Astronomy & Astrophysics
Maciek Wielgus
Summary: Under general assumptions on the accretion flow geometry, images of a black hole illuminated by electromagnetic radiation display a sequence of photon rings that can be compared with the properties of the underlying spacetime, providing a less model-dependent way to probe the spacetime metric and test general relativity and the Kerr hypothesis.
Article
Engineering, Aerospace
Vincent L. Fish et al.
ADVANCES IN SPACE RESEARCH
(2020)
Article
Engineering, Aerospace
Tao An et al.
ADVANCES IN SPACE RESEARCH
(2020)
Article
Engineering, Aerospace
Hendrik Linz et al.
ADVANCES IN SPACE RESEARCH
(2020)
Article
Engineering, Aerospace
Leonid I. Gurvits
ADVANCES IN SPACE RESEARCH
(2020)
Article
Multidisciplinary Sciences
Michael D. Johnson et al.
Article
Astronomy & Astrophysics
Samuel E. Gralla et al.
Article
Astronomy & Astrophysics
Freek Roelofs et al.
ASTRONOMY & ASTROPHYSICS
(2019)
Article
Astronomy & Astrophysics
F. Combes et al.
ASTRONOMY & ASTROPHYSICS
(2019)
Article
Astronomy & Astrophysics
Daniel C. M. Palumbo et al.
ASTROPHYSICAL JOURNAL
(2019)
Article
Astronomy & Astrophysics
Kazunori Akiyama et al.
ASTROPHYSICAL JOURNAL LETTERS
(2019)
Article
Astronomy & Astrophysics
Kazunori Akiyama et al.
ASTROPHYSICAL JOURNAL LETTERS
(2019)
Article
Astronomy & Astrophysics
Kazunori Akiyama et al.
ASTROPHYSICAL JOURNAL LETTERS
(2019)
Article
Astronomy & Astrophysics
Samuel E. Gralla et al.
Article
Astronomy & Astrophysics
F. Combes et al.
ASTRONOMY & ASTROPHYSICS
(2014)
Article
Astronomy & Astrophysics
N. S. Kardashev et al.
