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Expanding the Horizon of Black Hole Imaging with AtLAST

Kazunori Akiyama, Mariafelicia De Laurentis, Ziri Younsi, Yuto Akiyama, Dominic W. Pesce, Geoffrey C. Bower, Kazuhiro Hada, Jens Kauffmann, Shoko Koyama, Kotaro Moriyama, Derek-Ward Thompson

TL;DR

The paper argues that the current EHT horizon-scale imaging program is limited to two bright SMBHs and proposes expanding the accessible target pool by upgrading the array with AtLAST as a high-sensitivity southern anchor. It outlines a strategy built on Frequency Phase Transfer and multi-frequency capabilities to boost sensitivity and enable detailed, demographic studies of SMBH growth, accretion physics, and jet launching across a broad range of masses and environments, potentially leveraging angular resolutions approaching the photon ring. The authors project population-scale gains, including measurements of horizon-scale sizes and polarization structures, and discuss technical requirements such as wide-band, multi-frequency receivers and high-frequency capabilities, with space-based extensions (e.g., BHEX) offering even finer angular resolution. Overall, the work highlights the scientific impact of expanding horizon-scale imaging from a handful of nearby SMBHs to a large, diverse population, enabling stringent tests of gravity, accretion physics, and SMBH-galaxy coevolution.

Abstract

The Event Horizon Telescope (EHT) has directly resolved and imaged two supermassive black holes and opening a new window on black hole physics. However, the current array is limited to only these two brightest nearby targets. This white paper outlines how future EHT upgrades, anchored by the Atacama Large Aperture Submillimeter Telescope (AtLAST), will enable a transformative expansion of the accessible population of event-horizon-scale sources. By substantially improving sensitivity and multi-frequency capabilities, EHT+AtLAST will enable demographic studies of black hole growth, accretion physics, and jet launching across a wide range of masses, environments, and accretion states.

Expanding the Horizon of Black Hole Imaging with AtLAST

TL;DR

The paper argues that the current EHT horizon-scale imaging program is limited to two bright SMBHs and proposes expanding the accessible target pool by upgrading the array with AtLAST as a high-sensitivity southern anchor. It outlines a strategy built on Frequency Phase Transfer and multi-frequency capabilities to boost sensitivity and enable detailed, demographic studies of SMBH growth, accretion physics, and jet launching across a broad range of masses and environments, potentially leveraging angular resolutions approaching the photon ring. The authors project population-scale gains, including measurements of horizon-scale sizes and polarization structures, and discuss technical requirements such as wide-band, multi-frequency receivers and high-frequency capabilities, with space-based extensions (e.g., BHEX) offering even finer angular resolution. Overall, the work highlights the scientific impact of expanding horizon-scale imaging from a handful of nearby SMBHs to a large, diverse population, enabling stringent tests of gravity, accretion physics, and SMBH-galaxy coevolution.

Abstract

The Event Horizon Telescope (EHT) has directly resolved and imaged two supermassive black holes and opening a new window on black hole physics. However, the current array is limited to only these two brightest nearby targets. This white paper outlines how future EHT upgrades, anchored by the Atacama Large Aperture Submillimeter Telescope (AtLAST), will enable a transformative expansion of the accessible population of event-horizon-scale sources. By substantially improving sensitivity and multi-frequency capabilities, EHT+AtLAST will enable demographic studies of black hole growth, accretion physics, and jet launching across a wide range of masses, environments, and accretion states.
Paper Structure (3 sections, 3 figures)

This paper contains 3 sections, 3 figures.

Table of Contents

  1. Scientific context and motivation
  2. Science case
  3. Technical requirements and other VLBI science cases

Figures (3)

  • Figure 1: The first images of black holes captured by the Event Horizon Telescope (EHT), captivating billions of people across the globe and opening up a new window of black hole physics. This science white paper outlines the prospects for black hole physics enabled by an expanded sample of event-horizon-scale targets made possible by future EHT upgrades and extensions, including an extremely sensitive facility such as the Atacama Large Aperture Submillimeter Telescope (AtLAST).
  • Figure 1: SMBH population studies with EHT+AtLAST in 2030s. The black contours show the estimated cumulative number density of SMBHs as a function of shadow diameter and 230 GHz flux density Pesce2021. The white circles show the population of known SMBHs identified by the on-going ETHER survey Ramakrishnan_2023, yet being expanded toward 2030s. Colored lines indicate the measurement threshold values for the source size as a probe for the black hole mass (left), $\beta_2$ linear polarization polar Fourier mode as a probe for magnetic fields (middle) and the ring central depression as a probe for the black hole shadows (right). Those thresholds are estimated for a predicted ground-based multi-frequency EHT array in 2030s (EHT 2025+Haystack+OVRO+AMT) with synthetic EHT observations (see Pesce_2022 for methodology) for three cases: having only AtLAST (blue) or ALMA (green) in Chile, or having both two stations (red).
  • Figure 2: Examples of nearby SMBHs for horizon-scale studies accessible with future EHT upgrades, which cover a variety of different environments (see Zhang_2025 for details).