Special Issue "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 1742

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
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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

Manuscript Submission Information 

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Galaxies is an international peer-reviewed open access semimonthly journal published by MDPI.

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

Published Papers (3 papers)

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Research

Article
Measuring Photon Rings with the ngEHT
Galaxies 2022, 10(6), 111; https://doi.org/10.3390/galaxies10060111 (registering DOI) - 06 Dec 2022
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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
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Article
Expectations for Horizon-Scale Supermassive Black Hole Population Studies with the ngEHT
Galaxies 2022, 10(6), 109; https://doi.org/10.3390/galaxies10060109 - 02 Dec 2022
Viewed by 275
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
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Article
Relativistic Signatures of Flux Eruption Events near Black Holes
Galaxies 2022, 10(6), 107; https://doi.org/10.3390/galaxies10060107 - 24 Nov 2022
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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
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