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From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope...
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From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science

A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (15 November 2022) | Viewed by 76008

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Dr. Michael D. Johnson

E-Mail Website
Guest Editor
Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
Interests: black holes; VLBI; EHT; ngEHT
Dr. Shep Doeleman

E-Mail Website
Guest Editor
Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
Interests: black holes; VLBI; instrumentation
Dr. Jose L. Gómez

E-Mail Website
Guest Editor
Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía S/N, 18008 Granada, Spain
Interests: black holes; active galactic nuclei; relativistic jets; blazars; RMHD simulations
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In April 2019, the Event Horizon Telescope Collaboration successfully imaged the first supermassive black hole (M87*), opening a new era in detailed study of these exotic objects.  By sharply enhancing the capabilities of black hole imaging, the next-generation EHT (ngEHT) is poised to again revolutionize our view of horizon-scale physics. The ngEHT will enable the first movies of black hole accretion, produce high-dynamic-range images that connect black holes directly to their galactic-scale relativistic jets, and bring into range a larger population of black holes and explosive transients to explore.

This Special Issue will be the first series of papers developing the key science drivers and architecture of the ngEHT. Contributions will sharpen the ngEHT scientific vision and implementation by illuminating and proposing new possibilities in the following areas:

  • Fundamental physics (BH properties, tests of GR, EM/GW studies, dark matter, exotic compact objects).
  • Black holes and their cosmic context (SMBH formation and evolution, studies of SMBH binaries, multi-wavelength studies of black holes and jets, large-scale jet collimation and kinematics).
  • Accretion (probing accretion flow dynamics and structure, turbulence, plasma studies near a BH).
  • Jet launching (energy extraction from spinning BHs, black hole magnetospheres, jet kinematics and monitoring).
  • Transients and impulsive phenomena (incoherent transients including XRBs, TDEs, and SNe, GW precursor/afterglow studies).
  • New horizons (terrestrial applications such as geodesy, coherent sources such as magnetars, masers, FRBs, unexpected ngEHT applications, synergies with other next-generation facilities).
  • Algorithms and inference (imaging methods, model fitting to interferometric data, feature extraction, machine learning, parameter estimation, synthetic data, data challenges).
  • History, philosophy and cultural implications of building new instruments in the current era.
  • Advances in submillimeter VLBI instrumentation (antenna design, receivers, digital backends, data transport and correlation).
  • VLBI array design and optimization.

References:

https://ui.adsabs.harvard.edu/abs/2019BAAS...51g.256D/abstract

https://ui.adsabs.harvard.edu/abs/2021ApJS..253....5R/abstract

Dr. Michael D. Johnson
Dr. Shep Doeleman
Dr. Jose L. Gómez
Guest Editors

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this special issue is 0 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • black holes
  • general relativity
  • interferometry
  • radio instrumentation
  • accretion
  • relativistic jets
  • cosmology
  • very-long-baseline interferometry

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Published Papers (28 papers)

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Editorial

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3 pages, 2759 KiB  
Editorial
From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science
by Michael D. Johnson, Sheperd S. Doeleman, José L. Gómez and Avery E. Broderick
Galaxies 2023, 11(5), 92; https://doi.org/10.3390/galaxies11050092 - 22 Aug 2023
Cited by 1 | Viewed by 1310
Abstract
In April 2019, the Event Horizon Telescope (EHT) Collaboration successfully imaged a supermassive black hole (SMBH) for the first time, revealing the apparent “shadow” cast by the dark compact object M87* in the center of the elliptical galaxy Virgo A [...] [...] Read more.
In April 2019, the Event Horizon Telescope (EHT) Collaboration successfully imaged a supermassive black hole (SMBH) for the first time, revealing the apparent “shadow” cast by the dark compact object M87* in the center of the elliptical galaxy Virgo A [...] Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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Research

Jump to: Editorial, Other

35 pages, 19230 KiB  
Article
Reference Array and Design Consideration for the Next-Generation Event Horizon Telescope
by Sheperd S. Doeleman, John Barrett, Lindy Blackburn, Katherine L. Bouman, Avery E. Broderick, Ryan Chaves, Vincent L. Fish, Garret Fitzpatrick, Mark Freeman, Antonio Fuentes, José L. Gómez, Kari Haworth, Janice Houston, Sara Issaoun, Michael D. Johnson, Mark Kettenis, Laurent Loinard, Neil Nagar, Gopal Narayanan, Aaron Oppenheimer, Daniel C. M. Palumbo, Nimesh Patel, Dominic W. Pesce, Alexander W. Raymond, Freek Roelofs, Ranjani Srinivasan, Paul Tiede, Jonathan Weintroub and Maciek Wielgusadd Show full author list remove Hide full author list
Galaxies 2023, 11(5), 107; https://doi.org/10.3390/galaxies11050107 - 18 Oct 2023
Cited by 29 | Viewed by 3256
Abstract
We describe the process to design, architect, and implement a transformative enhancement of the Event Horizon Telescope (EHT). This program—the next-generation Event Horizon Telescope (ngEHT)—will form a networked global array of radio dishes capable of making high-fidelity real-time movies of supermassive black holes [...] Read more.
We describe the process to design, architect, and implement a transformative enhancement of the Event Horizon Telescope (EHT). This program—the next-generation Event Horizon Telescope (ngEHT)—will form a networked global array of radio dishes capable of making high-fidelity real-time movies of supermassive black holes (SMBH) and their emanating jets. This builds upon the EHT principally by deploying additional modest-diameter dishes to optimized geographic locations to enhance the current global mm/submm wavelength Very Long Baseline Interferometric (VLBI) array, which has, to date, utilized mostly pre-existing radio telescopes. The ngEHT program further focuses on observing at three frequencies simultaneously for increased sensitivity and Fourier spatial frequency coverage. Here, the concept, science goals, design considerations, station siting, and instrument prototyping are discussed, and a preliminary reference array to be implemented in phases is described. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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8 pages, 363 KiB  
Communication
Probing Neutrino Production in Blazars by Millimeter VLBI
by Yuri Y. Kovalev, Alexander V. Plavin, Alexander B. Pushkarev and Sergey V. Troitsky
Galaxies 2023, 11(4), 84; https://doi.org/10.3390/galaxies11040084 - 10 Jul 2023
Cited by 4 | Viewed by 1628
Abstract
The advancement of neutrino observatories has sparked a surge in multi-messenger astronomy. Multiple neutrino associations among blazars are reported while neutrino production sites are located within their central (sub)parsecs. Yet, many questions remain on the nature of those processes. The next generation Event [...] Read more.
The advancement of neutrino observatories has sparked a surge in multi-messenger astronomy. Multiple neutrino associations among blazars are reported while neutrino production sites are located within their central (sub)parsecs. Yet, many questions remain on the nature of those processes. The next generation Event Horizon Telescope (ngEHT) is uniquely positioned for these studies, as its high frequency and resolution can probe both the accretion disk region and the parsec-scale jet. This opens up new opportunities for connecting the two regions and unraveling the proton acceleration and neutrino production in blazars. We outline observational strategies for ngEHT and highlight what it can contribute to the multi-messenger study of blazars. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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38 pages, 9925 KiB  
Article
Key Science Goals for the Next-Generation Event Horizon Telescope
by Michael D. Johnson, Kazunori Akiyama, Lindy Blackburn, Katherine L. Bouman, Avery E. Broderick, Vitor Cardoso, Rob P. Fender, Christian M. Fromm, Peter Galison, José L. Gómez, Daryl Haggard, Matthew L. Lister, Andrei P. Lobanov, Sera Markoff, Ramesh Narayan, Priyamvada Natarajan, Tiffany Nichols, Dominic W. Pesce, Ziri Younsi, Andrew Chael, Koushik Chatterjee, Ryan Chaves, Juliusz Doboszewski, Richard Dodson, Sheperd S. Doeleman, Jamee Elder, Garret Fitzpatrick, Kari Haworth, Janice Houston, Sara Issaoun, Yuri Y. Kovalev, Aviad Levis, Rocco Lico, Alexandru Marcoci, Niels C. M. Martens, Neil M. Nagar, Aaron Oppenheimer, Daniel C. M. Palumbo, Angelo Ricarte, María  J. Rioja, Freek Roelofs, Ann C. Thresher, Paul Tiede, Jonathan Weintroub and Maciek Wielgusadd Show full author list remove Hide full author list
Galaxies 2023, 11(3), 61; https://doi.org/10.3390/galaxies11030061 - 24 Apr 2023
Cited by 55 | Viewed by 6776
Abstract
The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply [...] Read more.
The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply improve the angular resolution, dynamic range, and temporal coverage of the existing EHT observations. These improvements will uniquely enable a wealth of transformative new discoveries related to black hole science, extending from event-horizon-scale studies of strong gravity to studies of explosive transients to the cosmological growth and influence of supermassive black holes. Here, we present the key science goals for the ngEHT and their associated instrument requirements, both of which have been formulated through a multi-year international effort involving hundreds of scientists worldwide. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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23 pages, 2492 KiB  
Article
Accretion Flow Morphology in Numerical Simulations of Black Holes from the ngEHT Model Library: The Impact of Radiation Physics
by Koushik Chatterjee, Andrew Chael, Paul Tiede, Yosuke Mizuno, Razieh Emami, Christian Fromm, Angelo Ricarte, Lindy Blackburn, Freek Roelofs, Michael D. Johnson, Sheperd S. Doeleman, Philipp Arras, Antonio Fuentes, Jakob Knollmüller, Nikita Kosogorov, Greg Lindahl, Hendrik Müller, Nimesh Patel, Alexander Raymond, Efthalia Traianou and Justin Vegaadd Show full author list remove Hide full author list
Galaxies 2023, 11(2), 38; https://doi.org/10.3390/galaxies11020038 - 23 Feb 2023
Cited by 16 | Viewed by 2731
Abstract
In the past few years, the Event Horizon Telescope (EHT) has provided the first-ever event horizon-scale images of the supermassive black holes (BHs) M87* and Sagittarius A* (Sgr A*). The next-generation EHT project is an extension of the EHT [...] Read more.
In the past few years, the Event Horizon Telescope (EHT) has provided the first-ever event horizon-scale images of the supermassive black holes (BHs) M87* and Sagittarius A* (Sgr A*). The next-generation EHT project is an extension of the EHT array that promises larger angular resolution and higher sensitivity to the dim, extended flux around the central ring-like structure, possibly connecting the accretion flow and the jet. The ngEHT Analysis Challenges aim to understand the science extractability from synthetic images and movies to inform the ngEHT array design and analysis algorithm development. In this work, we compare the accretion flow structure and dynamics in numerical fluid simulations that specifically target M87* and Sgr A*, and were used to construct the source models in the challenge set. We consider (1) a steady-state axisymmetric radiatively inefficient accretion flow model with a time-dependent shearing hotspot, (2) two time-dependent single fluid general relativistic magnetohydrodynamic (GRMHD) simulations from the H-AMR code, (3) a two-temperature GRMHD simulation from the BHAC code, and (4) a two-temperature radiative GRMHD simulation from the KORAL code. We find that the different models exhibit remarkably similar temporal and spatial properties, except for the electron temperature, since radiative losses substantially cool down electrons near the BH and the jet sheath, signaling the importance of radiative cooling even for slowly accreting BHs such as M87*. We restrict ourselves to standard torus accretion flows, and leave larger explorations of alternate accretion models to future work. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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23 pages, 365 KiB  
Article
The Next Generation Event Horizon Telescope Collaboration: History, Philosophy, and Culture
by Peter Galison, Juliusz Doboszewski, Jamee Elder, Niels C. M. Martens, Abhay Ashtekar, Jonas Enander, Marie Gueguen, Elizabeth A. Kessler, Roberto Lalli, Martin Lesourd, Alexandru Marcoci, Sebastián Murgueitio Ramírez, Priyamvada Natarajan, James Nguyen, Luis Reyes-Galindo, Sophie Ritson, Mike D. Schneider, Emilie Skulberg, Helene Sorgner, Matthew Stanley, Ann C. Thresher, Jeroen Van Dongen, James Owen Weatherall, Jingyi Wu and Adrian Wüthrichadd Show full author list remove Hide full author list
Galaxies 2023, 11(1), 32; https://doi.org/10.3390/galaxies11010032 - 15 Feb 2023
Cited by 5 | Viewed by 7206
Abstract
This white paper outlines the plans of the History Philosophy Culture Working Group of the Next Generation Event Horizon Telescope Collaboration. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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20 pages, 8050 KiB  
Article
Enabling Transformational ngEHT Science via the Inclusion of 86 GHz Capabilities
by Sara Issaoun, Dominic W. Pesce, Freek Roelofs, Andrew Chael, Richard Dodson, María J. Rioja, Kazunori Akiyama, Romy Aran, Lindy Blackburn, Sheperd S. Doeleman, Vincent L. Fish, Garret Fitzpatrick, Michael D. Johnson, Gopal Narayanan, Alexander W. Raymond and Remo P. J. Tilanus
Galaxies 2023, 11(1), 28; https://doi.org/10.3390/galaxies11010028 - 10 Feb 2023
Cited by 13 | Viewed by 2219
Abstract
We present a case for significantly enhancing the utility and efficiency of the ngEHT by incorporating an additional 86 GHz observing band. In contrast to 230 or 345 GHz, weather conditions at the ngEHT sites are reliably good enough for 86 GHz to [...] Read more.
We present a case for significantly enhancing the utility and efficiency of the ngEHT by incorporating an additional 86 GHz observing band. In contrast to 230 or 345 GHz, weather conditions at the ngEHT sites are reliably good enough for 86 GHz to enable year-round observations. Multi-frequency imaging that incorporates 86 GHz observations would sufficiently augment the (u,v) coverage at 230 and 345 GHz to permit detection of the M87 jet structure without requiring EHT stations to join the array. The general calibration and sensitivity of the ngEHT would also be enhanced by leveraging frequency phase transfer techniques, whereby simultaneous observations at 86 GHz and higher-frequency bands have the potential to increase the effective coherence times from a few seconds to tens of minutes. When observation at the higher frequencies is not possible, there are opportunities for standalone 86 GHz science, such as studies of black hole jets and spectral lines. Finally, the addition of 86 GHz capabilities to the ngEHT would enable it to integrate into a community of other VLBI facilities—such as the GMVA and ngVLA—that are expected to operate at 86 GHz but not at the higher ngEHT observing frequencies. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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16 pages, 7482 KiB  
Article
Tracing Hot Spot Motion in Sagittarius A* Using the Next-Generation Event Horizon Telescope (ngEHT)
by Razieh Emami, Paul Tiede, Sheperd S. Doeleman, Freek Roelofs , Maciek Wielgus , Lindy Blackburn , Matthew Liska , Koushik Chatterjee , Bart Ripperda, Antonio Fuentes , Avery E. Broderick, Lars Hernquist , Charles Alcock , Ramesh Narayan, Randall Smith , Grant Tremblay, Angelo Ricarte, He Sun, Richard Anantua , Yuri Y. Kovalev , Priyamvada Natarajan and Mark Vogelsbergeradd Show full author list remove Hide full author list
Galaxies 2023, 11(1), 23; https://doi.org/10.3390/galaxies11010023 - 29 Jan 2023
Cited by 11 | Viewed by 2090
Abstract
We propose the tracing of the motion of a shearing hot spot near the Sgr A* source through a dynamical image reconstruction algorithm, StarWarps. Such a hot spot may form as the exhaust of magnetic reconnection in a current sheet near the black [...] Read more.
We propose the tracing of the motion of a shearing hot spot near the Sgr A* source through a dynamical image reconstruction algorithm, StarWarps. Such a hot spot may form as the exhaust of magnetic reconnection in a current sheet near the black hole horizon. A hot spot that is ejected from the current sheet into an orbit in the accretion disk may shear and diffuse due to instabilities at its boundary during its orbit, resulting in a distinct signature. We subdivide the motion into two different phases: the first phase refers to the appearance of the hot spot modeled as a bright blob, followed by a subsequent shearing phase. We employ different observational array configurations, including EHT (2017, 2022) and the next-generation Event Horizon Telescope (ngEHTp1, ngEHT) arrays, with several new sites added, and make dynamical image reconstructions for each of them. Subsequently, we infer the hot spot angular image location in the first phase, followed by the axes ratio and the ellipse area in the second phase. We focus on the direct observability of the orbiting hot spot in the sub-mm wavelength. Our analysis demonstrates that for this particular simulation, the newly added dishes are better able to trace the first phase as well as part of the second phase before the flux is reduced substantially, compared to the EHT arrays. The algorithm used in this work can be easily extended to other types of dynamics, as well as different shearing timescales. More simulations are required to prove whether the current set of newly proposed sites are sufficient to resolve any motions near variable sources, such as Sgr A*. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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9 pages, 4522 KiB  
Article
Multi-Wavelength and Multi-Messenger Studies Using the Next-Generation Event Horizon Telescope
by Rocco Lico, Svetlana G. Jorstad, Alan P. Marscher, Jose L. Gómez, Ioannis Liodakis, Rohan Dahale, Antxon Alberdi, Roman Gold, Efthalia Traianou, Teresa Toscano and Marianna Foschi
Galaxies 2023, 11(1), 17; https://doi.org/10.3390/galaxies11010017 - 14 Jan 2023
Cited by 6 | Viewed by 1808
Abstract
The next-generation Event Horizon Telescope (ngEHT) will provide us with the best opportunity to investigate supermassive black holes (SMBHs) at the highest possible resolution and sensitivity. With respect to the existing Event Horizon Telescope (EHT) array, the ngEHT will provide increased sensitivity and [...] Read more.
The next-generation Event Horizon Telescope (ngEHT) will provide us with the best opportunity to investigate supermassive black holes (SMBHs) at the highest possible resolution and sensitivity. With respect to the existing Event Horizon Telescope (EHT) array, the ngEHT will provide increased sensitivity and uv-coverage (with the addition of new stations), wider frequency coverage (from 86 GHz to 345 GHz and higher), finer resolution (<15 micro-arcseconds), and better monitoring capabilities. The ngEHT will offer a unique opportunity to deeply investigate the physics around SMBHs, such as the disk-jet connection, the mechanisms responsible for high-energy photon and neutrino events, and the role of magnetic fields in shaping relativistic jets, as well as the nature of binary SMBH systems. In this white paper we describe some ngEHT science cases in the context of multi-wavelength studies and synergies. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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15 pages, 2290 KiB  
Article
The Transformational Power of Frequency Phase Transfer Methods for ngEHT
by María J. Rioja, Richard Dodson and Yoshiharu Asaki
Galaxies 2023, 11(1), 16; https://doi.org/10.3390/galaxies11010016 - 12 Jan 2023
Cited by 20 | Viewed by 1922
Abstract
(Sub) mm VLBI observations are strongly hindered by limited sensitivity, with the fast tropospheric fluctuations being the dominant culprit. We predict great benefits from applying next-generation frequency phase transfer calibration techniques for the next generation Event Horizon Telescope (ngEHT), using simultaneous multi-frequency observations. [...] Read more.
(Sub) mm VLBI observations are strongly hindered by limited sensitivity, with the fast tropospheric fluctuations being the dominant culprit. We predict great benefits from applying next-generation frequency phase transfer calibration techniques for the next generation Event Horizon Telescope (ngEHT), using simultaneous multi-frequency observations. We present comparative simulation studies to characterise its performance, the optimum configurations, and highlight the benefits of including observations at 85 GHz along with the 230 and 340 GHz bands. The results show a transformational impact on the ngEHT array capabilities, with orders of magnitude improved sensitivity, observations routinely possible over the whole year, and ability to carry out micro-arcsecond astrometry measurements at the highest frequencies, amongst others. This will enable the addressing of a host of innovative open scientific questions in astrophysics. We present a solution for highly scatter-broadened sources such as SgrA*, a prime ngEHT target. We conclude that adding the 85 GHz band provides a pathway to an optimum and robust performance for ngEHT in sub-millimeter VLBI, and strongly recommmend its inclusion in the simultaneous multi-frequency receiver design. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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18 pages, 2866 KiB  
Article
Event Horizon and Environs (ETHER): A Curated Database for EHT and ngEHT Targets and Science
by Venkatessh Ramakrishnan, Neil Nagar, Vicente Arratia, Joaquín Hernández-Yévenes, Dominic W. Pesce, Dhanya G. Nair, Bidisha Bandyopadhyay, Catalina Medina-Porcile, Thomas P. Krichbaum, Sheperd Doeleman, Angelo Ricarte, Vincent L. Fish, Lindy Blackburn, Heino Falcke, Geoffrey Bower and Priyamvada Natarajan
Galaxies 2023, 11(1), 15; https://doi.org/10.3390/galaxies11010015 - 12 Jan 2023
Cited by 11 | Viewed by 2907
Abstract
The next generation Event Horizon Telescope (ngEHT) will observe multiple supermassive black hole (SMBH) candidates down to a few tens of mJy, and profoundly transform our understanding of the local SMBH population. Given the impossibility of large-area high-resolution millimeter surveys, multi-frequency spectral energy [...] Read more.
The next generation Event Horizon Telescope (ngEHT) will observe multiple supermassive black hole (SMBH) candidates down to a few tens of mJy, and profoundly transform our understanding of the local SMBH population. Given the impossibility of large-area high-resolution millimeter surveys, multi-frequency spectral energy densities (SEDs), and models are required to both identify source samples tailored to specific science goals, and to predict the feasibility of detection of individual interesting sources. Here, we present the Event Horizon and Environs (ETHER) source and SED model database whose primary use is to enable the selection and optimization of targets for EHT and ngEHT science. The living ETHER database currently consolidates 1.6 million black hole mass estimates, ∼15,500 milliarcsec-scale radio fluxes, ∼14,000 hard X-ray fluxes (expected to grow by factor ≳40 with the eROSITA data release) and SED information as obtained from catalogs and database queries, the literature, and our own new observations. Jet and accretion flow models are fit to individual SEDs in an automated way in order to predict the ngEHT observable fluxes from the jet base and accretion inflow. The database can be filtered by parameters or cross matched to a user source list, with the automated SED fitting models optionally fine tuned by the user. We have identified an initial ngEHT ‘gold sample’ for jet base studies and potentially black hole shadows; this sample will grow significantly in the coming years. While the ngEHT requires and will best exploit the ETHER database, six (eleven) ETHER sources have already been observed (scheduled) with the EHT in 2022 (2023), and the database has wide ranging applications in galaxy and black hole mass evolution studies. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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14 pages, 2447 KiB  
Article
Prospects of GPU Tensor Core Correlation for the SMA and the ngEHT
by Wei Yu, John W. Romein, L. Jonathan Dursi, Ru-Sen Lu, Adrian Pope, Gareth Callanan, Dominic W. Pesce, Lindy Blackburn, Bruce Merry, Ranjani Srinivasan, Jongsoo Kim and Jonathan Weintroub
Galaxies 2023, 11(1), 13; https://doi.org/10.3390/galaxies11010013 - 11 Jan 2023
Cited by 3 | Viewed by 2336
Abstract
Building on the base of the existing telescopes of the Event Horizon Telescope (EHT) and ALMA, the next-generation EHT (ngEHT) aspires to deploy ∼10 more stations. The ngEHT targets an angular resolution of ∼15 microarcseconds. This resolution is achieved using Very Long Baseline [...] Read more.
Building on the base of the existing telescopes of the Event Horizon Telescope (EHT) and ALMA, the next-generation EHT (ngEHT) aspires to deploy ∼10 more stations. The ngEHT targets an angular resolution of ∼15 microarcseconds. This resolution is achieved using Very Long Baseline Interferometry (VLBI) at the shortest radio wavelengths ∼1 mm. The Submillimeter Array (SMA) is both a standalone radio interferometer and a station of the EHT and will conduct observations together with the new ngEHT stations. The future EHT + ngEHT array requires a dedicated correlator to process massive amounts of data. The current correlator-beamformer (CBF) of the SMA would also benefit from an upgrade, to expand the SMA’s bandwidth and also match the EHT + ngEHT observations. The two correlators share the same basic architecture, so that the development time can be reduced using common technology for both applications. This paper explores the prospects of using Tensor Core Graphics Processing Units (TC GPU) as the primary digital signal processing (DSP) engine. This paper describes the architecture, aspects of the detailed design, and approaches to performance optimization of a CBF using the “FX” approach. We describe some of the benefits and challenges of the TC GPU approach. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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30 pages, 13921 KiB  
Article
The ngEHT Analysis Challenges
by Freek Roelofs, Lindy Blackburn, Greg Lindahl, Sheperd S. Doeleman, Michael D. Johnson, Philipp Arras, Koushik Chatterjee, Razieh Emami, Christian Fromm, Antonio Fuentes, Jakob Knollmüller, Nikita Kosogorov, Hendrik Müller, Nimesh Patel, Alexander Raymond, Paul Tiede, Efthalia Traianou and Justin Vega
Galaxies 2023, 11(1), 12; https://doi.org/10.3390/galaxies11010012 - 10 Jan 2023
Cited by 23 | Viewed by 2662
Abstract
The next-generation Event Horizon Telescope (ngEHT) will be a significant enhancement of the Event Horizon Telescope (EHT) array, with ∼10 new antennas and instrumental upgrades of existing antennas. The increased uv-coverage, sensitivity, and frequency coverage allow a wide range of new [...] Read more.
The next-generation Event Horizon Telescope (ngEHT) will be a significant enhancement of the Event Horizon Telescope (EHT) array, with ∼10 new antennas and instrumental upgrades of existing antennas. The increased uv-coverage, sensitivity, and frequency coverage allow a wide range of new science opportunities to be explored. The ngEHT Analysis Challenges have been launched to inform the development of the ngEHT array design, science objectives, and analysis pathways. For each challenge, synthetic EHT and ngEHT datasets are generated from theoretical source models and released to the challenge participants, who analyze the datasets using image reconstruction and other methods. The submitted analysis results are evaluated with quantitative metrics. In this work, we report on the first two ngEHT Analysis Challenges. These have focused on static and dynamical models of M87* and Sgr A* and shown that high-quality movies of the extended jet structure of M87* and near-horizon hourly timescale variability of Sgr A* can be reconstructed by the reference ngEHT array in realistic observing conditions using current analysis algorithms. We identify areas where there is still room for improvement of these algorithms and analysis strategies. Other science cases and arrays will be explored in future challenges. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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14 pages, 7565 KiB  
Article
Probing Plasma Composition with the Next Generation Event Horizon Telescope (ngEHT)
by Razieh Emami, Richard Anantua, Angelo Ricarte, Sheperd S. Doeleman, Avery Broderick, George Wong, Lindy Blackburn, Maciek Wielgus, Ramesh Narayan, Grant Tremblay, Charles Alcock, Lars Hernquist, Randall Smith, Matthew Liska , Priyamvada Natarajan, Mark Vogelsberger, Brandon Curd and Joana A. Kramer 
Galaxies 2023, 11(1), 11; https://doi.org/10.3390/galaxies11010011 - 10 Jan 2023
Cited by 8 | Viewed by 1753
Abstract
We explore the plasma matter content in the innermost accretion disk/jet in M87* as relevant for an enthusiastic search for the signatures of anti-matter in the next generation of the Event Horizon Telescope (ngEHT). We model the impact of non-zero positron-to-electron ratio using [...] Read more.
We explore the plasma matter content in the innermost accretion disk/jet in M87* as relevant for an enthusiastic search for the signatures of anti-matter in the next generation of the Event Horizon Telescope (ngEHT). We model the impact of non-zero positron-to-electron ratio using different emission models, including a constant electron to magnetic pressure (constant βe model) with a population of non-thermal electrons as well as an R-beta model populated with thermal electrons. In the former case, we pick a semi-analytic fit to the force-free region of a general relativistic magnetohydrodynamic (GRMHD) simulation, while in the latter case, we analyze the GRMHD simulations directly. In both cases, positrons are being added at the post-processing level. We generate polarized images and spectra for some of these models and find out that at the radio frequencies, both of the linear and the circular polarizations are enhanced with every pair added. On the contrary, we show that, at higher frequencies, a substantial positron fraction washes out the circular polarization. We report strong degeneracies between different emission models and the positron fraction, though our non-thermal models show more sensitivities to the pair fraction than the thermal models. We conclude that a large theoretical image library is indeed required to fully understand the trends probed in this study, and to place them in the context of a large set of parameters which also affect polarimetric images, such as magnetic field strength, black hole spin, and detailed aspects of the electron temperature and the distribution function. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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12 pages, 441 KiB  
Article
Spectral Line VLBI Studies Using the ngEHT
by Dong-Jin Kim and Vincent Fish
Galaxies 2023, 11(1), 10; https://doi.org/10.3390/galaxies11010010 - 6 Jan 2023
Cited by 3 | Viewed by 1860
Abstract
Spectroscopy in the mm/sub-mm wavelength range is a powerful tool to study the gaseous medium in various astrophysical environments. The next generation Event Horizon Telescope (ngEHT) equipped with a wide-bandwidth backend system has great potential for science using high angular resolution spectroscopy. Spectral [...] Read more.
Spectroscopy in the mm/sub-mm wavelength range is a powerful tool to study the gaseous medium in various astrophysical environments. The next generation Event Horizon Telescope (ngEHT) equipped with a wide-bandwidth backend system has great potential for science using high angular resolution spectroscopy. Spectral line VLBI studies using the ngEHT will enable us to scrutinize compact astrophysical objects obscured by an optically thick medium on unprecedented angular scales. However, the capabilities of ngEHT for spectroscopy and specific scientific applications have not been properly envisioned. In this white paper, we briefly address science cases newly achievable via spectral line VLBI observations in the mm/sub-mm wavelength ranges, and suggest technical requirements to facilitate spectral line VLBI studies in the ngEHT era. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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9 pages, 5954 KiB  
Article
The Haystack Telescope as an Astronomical Instrument
by Jens Kauffmann, Ganesh Rajagopalan, Kazunori Akiyama, Vincent Fish, Colin Lonsdale, Lynn D. Matthews and Thushara G.S. Pillai
Galaxies 2023, 11(1), 9; https://doi.org/10.3390/galaxies11010009 - 4 Jan 2023
Cited by 7 | Viewed by 2613
Abstract
The Haystack Telescope is an antenna with a diameter of 37 m and an elevation-dependent surface accuracy of ≤100μm that is capable of millimeter-wave observations. The radome-enclosed instrument serves as a radar sensor for space situational awareness, with about one-third [...] Read more.
The Haystack Telescope is an antenna with a diameter of 37 m and an elevation-dependent surface accuracy of ≤100μm that is capable of millimeter-wave observations. The radome-enclosed instrument serves as a radar sensor for space situational awareness, with about one-third of the time available for research by MIT Haystack Observatory. Ongoing testing with the K-band (18–26 GHz) and W-band receivers (currently 85–93 GHz) is preparing the inclusion of the telescope into the Event Horizon Telescope (EHT) array and the use as a single-dish research telescope. Given its geographic location, the addition of the Haystack Telescope to current and future versions of the EHT array would substantially improve the image quality. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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12 pages, 6347 KiB  
Article
Evaluation of a Candidate Site in the Tibetan Plateau towards the Next Generation Event Horizon Telescope
by Wei Yu, Ru-Sen Lu, Zhi-Qiang Shen and Jonathan Weintroub
Galaxies 2023, 11(1), 7; https://doi.org/10.3390/galaxies11010007 - 26 Dec 2022
Cited by 2 | Viewed by 1587
Abstract
In order to enhance the imaging capabilities of the Event Horizon Telescope (EHT) and capture the first black hole movies, the next-generation EHT (ngEHT) team is building new stations. Most stations of the EHT and ngEHT project are located in the Western Hemisphere, [...] Read more.
In order to enhance the imaging capabilities of the Event Horizon Telescope (EHT) and capture the first black hole movies, the next-generation EHT (ngEHT) team is building new stations. Most stations of the EHT and ngEHT project are located in the Western Hemisphere, leaving a large vacancy in the Eastern Hemisphere. Located in the center of the Eastern Hemisphere, the Tibetan Plateau is believed to have excellent sites for (sub)millimeter astronomical radio observations. Building a telescope here could help to fill this vacancy. In this study, we evaluated the meteorological conditions of a candidate site (Shigatse, hereafter SG) with good astronomical infrastructure for this telescope. The evaluation results show that the precipitable water vapor (PWV) values of the SG site are lower than 4 mm during winter and spring, comparable to those of some existing EHT stations, and the zenith transmittances at 230 GHz and 345 GHz during March and April are excellent. We simulated VLBI observations of Sgr A* and M87 based on the conditions of the SG site and those of other existing/planned (sub)millimeter telescopes with mutual visibility at 230 GHz. The results demonstrated that images of Sgr A* and M87 could be well reconstructed, indicating that the SG site is a good candidate for future EHT/ngEHT observations. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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14 pages, 917 KiB  
Article
The ngEHT’s Role in Measuring Supermassive Black Hole Spins
by Angelo Ricarte, Paul Tiede, Razieh Emami, Aditya Tamar and Priyamvada Natarajan
Galaxies 2023, 11(1), 6; https://doi.org/10.3390/galaxies11010006 - 26 Dec 2022
Cited by 19 | Viewed by 2308
Abstract
While supermassive black-hole masses have been cataloged across cosmic time, only a few dozen of them have robust spin measurements. By extending and improving the existing Event Horizon Telescope (EHT) array, the next-generation Event Horizon Telescope (ngEHT) will enable multifrequency, polarimetric movies on [...] Read more.
While supermassive black-hole masses have been cataloged across cosmic time, only a few dozen of them have robust spin measurements. By extending and improving the existing Event Horizon Telescope (EHT) array, the next-generation Event Horizon Telescope (ngEHT) will enable multifrequency, polarimetric movies on event-horizon scales, which will place new constraints on the space-time and accretion flow. By combining this information, it is anticipated that the ngEHT may be able to measure tens of supermassive black-hole masses and spins. In this white paper, we discuss existing spin measurements and many proposed techniques with which the ngEHT could potentially measure spins of target supermassive black holes. Spins measured by the ngEHT would represent a completely new sample of sources that, unlike pre-existing samples, would not be biased towards objects with high accretion rates. Such a sample would provide new insights into the accretion, feedback, and cosmic assembly of supermassive black holes. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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16 pages, 3948 KiB  
Article
How Spatially Resolved Polarimetry Informs Black Hole Accretion Flow Models
by Angelo Ricarte, Michael D. Johnson, Yuri Y. Kovalev, Daniel C. M. Palumbo and Razieh Emami
Galaxies 2023, 11(1), 5; https://doi.org/10.3390/galaxies11010005 - 25 Dec 2022
Cited by 18 | Viewed by 2063
Abstract
The Event Horizon Telescope (EHT) Collaboration has successfully produced images of two supermassive black holes, enabling novel tests of black holes and their accretion flows on horizon scales. The EHT has so far published total intensity and linear polarization images, while upcoming images [...] Read more.
The Event Horizon Telescope (EHT) Collaboration has successfully produced images of two supermassive black holes, enabling novel tests of black holes and their accretion flows on horizon scales. The EHT has so far published total intensity and linear polarization images, while upcoming images may include circular polarization, rotation measure, and spectral index, each of which reveals different aspects of the plasma and space-time. The next-generation EHT (ngEHT) will greatly enhance these studies through wider recorded bandwidths and additional stations, leading to greater signal-to-noise, orders of magnitude improvement in dynamic range, multi-frequency observations, and horizon-scale movies. In this paper, we review how each of these different observables informs us about the underlying properties of the plasma and the spacetime, and we discuss why polarimetric studies are well-suited to measurements with sparse, long-baseline coverage. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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22 pages, 17467 KiB  
Article
Emission Modeling in the EHT–ngEHT Age
by Richard Anantua, Joaquín Dúran, Nathan Ngata, Lani Oramas, Jan Röder, Razieh Emami, Angelo Ricarte, Brandon Curd, Avery E. Broderick, Jeremy Wayland, George N. Wong, Sean Ressler, Nitya Nigam and Emmanuel Durodola
Galaxies 2023, 11(1), 4; https://doi.org/10.3390/galaxies11010004 - 23 Dec 2022
Cited by 4 | Viewed by 2971
Abstract
This work proposes a methodology for testing phenomenologically motivated emission processes that account for the flux and polarization distribution and global structure of the 230 GHz sources imaged by the Event Horizon Telescope (EHT): Messier (M)87* and Sagittarius (Sgr) A*. We introduce into [...] Read more.
This work proposes a methodology for testing phenomenologically motivated emission processes that account for the flux and polarization distribution and global structure of the 230 GHz sources imaged by the Event Horizon Telescope (EHT): Messier (M)87* and Sagittarius (Sgr) A*. We introduce into general relativistic magnetohydrodynamic (GRMHD) simulations some novel models to bridge the largely uncertain mechanisms by which high-energy particles in jet/accretion flow/black hole (JAB) system plasmas attain billion-degree temperatures and emit synchrotron radiation. The “Observing” JAB Systems methodology then partitions the simulation to apply different parametric models to regions governed by different plasma physics—an advance over methods in which one parametrization is used over simulation regions spanning thousands of gravitational radii from the central supermassive black hole. We present several classes of viewing-angle-dependent morphologies and highlight signatures of piecewise modeling and positron effects, including a MAD/SANE dichotomy in which polarized maps appear dominated by intrinsic polarization in the MAD case and by Faraday effects in the SANE case. The library of images thus produced spans a wide range of morphologies awaiting discovery by the groundbreaking EHT instrument and its yet more sensitive, higher-resolution next-generation counterpart, ngEHT. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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9 pages, 663 KiB  
Article
Applications of the Source-Frequency Phase-Referencing Technique for ngEHT Observations
by Wu Jiang, Guang-Yao Zhao, Zhi-Qiang Shen, María J. Rioja, Richard Dodson, Ilje Cho, Shan-Shan Zhao, Marshall Eubanks and Ru-Sen Lu
Galaxies 2023, 11(1), 3; https://doi.org/10.3390/galaxies11010003 - 21 Dec 2022
Cited by 7 | Viewed by 2267
Abstract
The source-frequency phase-referencing (SFPR) technique has been demonstrated to have great advantages for mm-VLBI observations. By implementing simultaneous multi-frequency receiving systems on the next-generation Event Horizon Telescope (ngEHT) antennas, it is feasible to carry out a frequency phase transfer (FPT) which could calibrate [...] Read more.
The source-frequency phase-referencing (SFPR) technique has been demonstrated to have great advantages for mm-VLBI observations. By implementing simultaneous multi-frequency receiving systems on the next-generation Event Horizon Telescope (ngEHT) antennas, it is feasible to carry out a frequency phase transfer (FPT) which could calibrate the non-dispersive propagation errors and significantly increase the phase coherence in the visibility data. Such an increase offers an efficient approach for a weak source or structure detection. The SFPR also makes it possible for high-precision astrometry, including the core-shift measurements up to sub-mm wavelengths for Sgr A*, M 87*, etc. We also briefly discuss the technical and scheduling considerations for future SFPR observations with the ngEHT. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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17 pages, 4141 KiB  
Article
The Role of the Large Millimeter Telescope in Black Hole Science with the Next-Generation Event Horizon Telescope
by Sandra Bustamante, Lindy Blackburn, Gopal Narayanan, F. Peter Schloerb and David Hughes
Galaxies 2023, 11(1), 2; https://doi.org/10.3390/galaxies11010002 - 21 Dec 2022
Cited by 7 | Viewed by 2233
Abstract
The landmark black hole images recently taken by the Event Horizon Telescope (EHT) have allowed the detailed study of the immediate surroundings of supermassive black holes (SMBHs) via direct imaging. These tantalizing early results motivate an expansion of the array, its instrumental capabilities, [...] Read more.
The landmark black hole images recently taken by the Event Horizon Telescope (EHT) have allowed the detailed study of the immediate surroundings of supermassive black holes (SMBHs) via direct imaging. These tantalizing early results motivate an expansion of the array, its instrumental capabilities, and dedicated long-term observations to resolve and track faint dynamical features in the black hole jet and accretion flow. The next-generation Event Horizon Telescope (ngEHT) is a project that plans to double the number of telescopes in the VLBI array and extend observations to dual-frequency 230 + 345 GHz, improving total and snapshot coverage, as well as observational agility. The Large Millimeter Telescope (LMT) is the largest sub-mm single dish telescope in the world at 50 m in diameter, and both its sensitivity and central location within the EHT array make it a key anchor station for the other telescopes. In this work, we detail current and planned future upgrades to the LMT that will directly impact its Very Large Baseline Interferometry (VLBI) performance for the EHT and ngEHT. These include the commissioning of a simultaneous 230 + 345 GHz dual-frequency, dual-polarization heterodyne receiver, improved real-time surface measurement and setting, and improvements to thermal stability, which should enable expanded daytime operation. We test and characterize the performance of an improved LMT joining future ngEHT observations through simulated observations of Sgr A* and M 87. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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8 pages, 655 KiB  
Article
Millimeter/Submillimeter VLBI with a Next Generation Large Radio Telescope in the Atacama Desert
by Kazunori Akiyama, Jens Kauffmann, Lynn D. Matthews, Kotaro Moriyama, Shoko Koyama and Kazuhiro Hada
Galaxies 2023, 11(1), 1; https://doi.org/10.3390/galaxies11010001 - 20 Dec 2022
Cited by 11 | Viewed by 2364
Abstract
The proposed next generation Event Horizon Telescope (ngEHT) concept envisions the imaging of various astronomical sources on scales of microarcseconds in unprecedented detail with at least two orders of magnitude improvement in the image dynamic ranges by extending the Event Horizon Telescope (EHT). [...] Read more.
The proposed next generation Event Horizon Telescope (ngEHT) concept envisions the imaging of various astronomical sources on scales of microarcseconds in unprecedented detail with at least two orders of magnitude improvement in the image dynamic ranges by extending the Event Horizon Telescope (EHT). A key technical component of ngEHT is the utilization of large aperture telescopes to anchor the entire array, allowing the connection of less sensitive stations through highly sensitive fringe detections to form a dense network across the planet. Here, we introduce two projects for planned next generation large radio telescopes in the 2030s on the Chajnantor Plateau in the Atacama desert in northern Chile, the Large Submillimeter Telescope (LST) and the Atacama Large Aperture Submillimeter Telescope (AtLAST). Both are designed to have a 50-meter diameter and operate at the planned ngEHT frequency bands of 86, 230 and 345 GHz. A large aperture of 50 m that is co-located with two existing EHT stations, the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Pathfinder Experiment (APEX) Telescope in the excellent observing site of the Chajnantor Plateau, will offer excellent capabilities for highly sensitive, multi-frequency, and time-agile millimeter very long baseline interferometry (VLBI) observations with accurate data calibration relevant to key science cases of ngEHT. In addition to ngEHT, its unique location in Chile will substantially improve angular resolutions of the planned Next Generation Very Large Array in North America or any future global millimeter VLBI arrays if combined. LST and AtLAST will be a key element enabling transformative science cases with next-generation millimeter/submillimeter VLBI arrays. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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18 pages, 1244 KiB  
Article
Modeling Reconstructed Images of Jets Launched by SANE Super-Eddington Accretion Flows around SMBHs with the ngEHT
by Brandon Curd, Razieh Emami, Freek Roelofs and Richard Anantua
Galaxies 2022, 10(6), 117; https://doi.org/10.3390/galaxies10060117 - 13 Dec 2022
Cited by 5 | Viewed by 2059
Abstract
Tidal disruption events (TDEs) around supermassive black holes (SMBHs) are a potential laboratory to study super-Eddington accretion disks and sometimes result in powerful jets or outflows which may shine in the radio and sub-millimeter bands. In this work, we modeled the thermal synchrotron [...] Read more.
Tidal disruption events (TDEs) around supermassive black holes (SMBHs) are a potential laboratory to study super-Eddington accretion disks and sometimes result in powerful jets or outflows which may shine in the radio and sub-millimeter bands. In this work, we modeled the thermal synchrotron emission of jets by general relativistic radiation magneto-hydrodynamics (GRRMHD) simulations of a BH accretion disk/jet system which assumed the TDE resulted in a magnetized accretion disk around a BH accreting at ∼12–25 times the Eddington accretion rate. Through synthetic observations with the Next Generation Event Horizon Telescope (ngEHT) and an image reconstruction analysis, we demonstrate that TDE jets may provide compelling targets within the context of the models explored in this work. In particular, we found that jets launched by a SANE super-Eddington disk around a spin a*=0.9 reach the ngEHT detection threshold at large distances (up to 100 Mpc in this work). A two-temperature plasma in the jet or weaker jets, such as a spin a*=0 model, requires a much closer distance, as we demonstrate detection at 10 Mpc for limiting cases of a*=0,R=1 or a*=0.9,R=20. We also demonstrate that TDE jets may appear as superluminal sources if the BH is rapidly rotating and the jet is viewed nearly face on. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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17 pages, 3715 KiB  
Article
Measuring Photon Rings with the ngEHT
by Paul Tiede, Michael D. Johnson, Dominic W. Pesce, Daniel C. M. Palumbo, Dominic O. Chang and Peter Galison
Galaxies 2022, 10(6), 111; https://doi.org/10.3390/galaxies10060111 - 6 Dec 2022
Cited by 33 | Viewed by 2382
Abstract
General relativity predicts that images of optically thin accretion flows around black holes should generically have a “photon ring”, composed of a series of increasingly sharp subrings that correspond to increasingly strongly lensed emission near the black hole. Because the effects of lensing [...] Read more.
General relativity predicts that images of optically thin accretion flows around black holes should generically have a “photon ring”, composed of a series of increasingly sharp subrings that correspond to increasingly strongly lensed emission near the black hole. Because the effects of lensing are determined by the spacetime curvature, the photon ring provides a pathway to precise measurements of the black hole properties and tests of the Kerr metric. We explore the prospects for detecting and measuring the photon ring using very long baseline interferometry (VLBI) with the Event Horizon Telescope (EHT) and the next-generation EHT (ngEHT). We present a series of tests using idealized self-fits to simple geometrical models and show that the EHT observations in 2017 and 2022 lack the angular resolution and sensitivity to detect the photon ring, while the improved coverage and angular resolution of ngEHT at 230 GHz and 345 GHz is sufficient for these models. We then analyze detection prospects using more realistic images from general relativistic magnetohydrodynamic simulations by applying “hybrid imaging”, which simultaneously models two components: a flexible raster image (to capture the direct emission) and a ring component. Using the Bayesian VLBI modeling package Comrade.jl, we show that the results of hybrid imaging must be interpreted with extreme caution for both photon ring detection and measurement—hybrid imaging readily produces false positives for a photon ring, and its ring measurements do not directly correspond to the properties of the photon ring. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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10 pages, 1086 KiB  
Article
Expectations for Horizon-Scale Supermassive Black Hole Population Studies with the ngEHT
by Dominic W. Pesce, Daniel C. M. Palumbo, Angelo Ricarte, Avery E. Broderick, Michael D. Johnson, Neil M. Nagar, Priyamvada Natarajan and José L. Gómez
Galaxies 2022, 10(6), 109; https://doi.org/10.3390/galaxies10060109 - 2 Dec 2022
Cited by 12 | Viewed by 2133
Abstract
We present estimates for the number of supermassive black holes (SMBHs) for which the next-generation Event Horizon Telescope (ngEHT) can identify the black hole “shadow”, along with estimates for how many black hole masses and spins the ngEHT can expect to constrain using [...] Read more.
We present estimates for the number of supermassive black holes (SMBHs) for which the next-generation Event Horizon Telescope (ngEHT) can identify the black hole “shadow”, along with estimates for how many black hole masses and spins the ngEHT can expect to constrain using measurements of horizon-resolved emission structure. Building on prior theoretical studies of SMBH accretion flows and analyses carried out by the Event Horizon Telescope (EHT) collaboration, we construct a simple geometric model for the polarized emission structure around a black hole, and we associate parameters of this model with the three physical quantities of interest. We generate a large number of realistic synthetic ngEHT datasets across different assumed source sizes and flux densities, and we estimate the precision with which our defined proxies for physical parameters could be measured from these datasets. Under April weather conditions and using an observing frequency of 230 GHz, we predict that a “Phase 1” ngEHT can potentially measure ∼50 black hole masses, ∼30 black hole spins, and ∼7 black hole shadows across the entire sky. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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14 pages, 29582 KiB  
Article
Relativistic Signatures of Flux Eruption Events near Black Holes
by Zachary Gelles, Koushik Chatterjee, Michael Johnson, Bart Ripperda and Matthew Liska
Galaxies 2022, 10(6), 107; https://doi.org/10.3390/galaxies10060107 - 24 Nov 2022
Cited by 10 | Viewed by 2029
Abstract
Images of supermassive black holes produced using very long baseline interferometry provide a pathway to directly observing effects of a highly curved spacetime, such as a bright “photon ring” that arises from strongly lensed emission. In addition, the emission near supermassive black holes [...] Read more.
Images of supermassive black holes produced using very long baseline interferometry provide a pathway to directly observing effects of a highly curved spacetime, such as a bright “photon ring” that arises from strongly lensed emission. In addition, the emission near supermassive black holes is highly variable, with bright high-energy flares regularly observed. We demonstrate that intrinsic variability can introduce prominent associated changes in the relative brightness of the photon ring. We analyze both semianalytic toy models and GRMHD simulations with magnetic flux eruption events, showing that they each exhibit a characteristic “loop” in the space of relative photon ring brightness versus total flux density. For black holes viewed at high inclination, the relative photon ring brightness can change by an order of magnitude, even with variations in total flux density that are comparatively mild. We show that gravitational lensing, Doppler boosting, and magnetic field structure all significantly affect this feature, and we discuss the prospects for observing it in observations of M87∗ and Sgr A∗ with the next-generation Event Horizon Telescope. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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6 pages, 299 KiB  
Technical Note
Progress on the Haystack Observatory Postprocessing System
by Daniel Hoak, John Barrett, Geoffrey Crew and Violet Pfeiffer
Galaxies 2022, 10(6), 119; https://doi.org/10.3390/galaxies10060119 - 17 Dec 2022
Cited by 3 | Viewed by 1784
Abstract
The Haystack Observatory Postprocessing System (HOPS) is a multipurpose tool for post-correlation calibration and data analysis in Very-Long Baseline Interferometry experiments. The requirements on stations, baselines, and bandwidth for the Next Generation Event Horizon Telescope (ngEHT) have motivated a significant refactoring of the [...] Read more.
The Haystack Observatory Postprocessing System (HOPS) is a multipurpose tool for post-correlation calibration and data analysis in Very-Long Baseline Interferometry experiments. The requirements on stations, baselines, and bandwidth for the Next Generation Event Horizon Telescope (ngEHT) have motivated a significant refactoring of the HOPS codebase. In this paper, we present the requirements, specifications, and design of HOPS 4.0 and the current state of the refactoring, and we discuss future work. Full article
(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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