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1. Expectations for Horizon-Scale Supermassive Black Hole Population Studies with the ngEHT

   https://doi.org/10.3390/galaxies10060109  

   Pesce, Dominic W.; Palumbo, Daniel C.; Ricarte, Angelo; Broderick, Avery E.; Johnson, Michael D.; Nagar, Neil M.; Natarajan, Priyamvada; Gómez, José L. (December 2022, Galaxies)

   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. 

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2. Key Science Goals for the Next-Generation Event Horizon Telescope

   https://doi.org/10.3390/galaxies11030061  

   Johnson, Michael D.; Akiyama, Kazunori; Blackburn, Lindy; Bouman, Katherine L.; Broderick, Avery E.; Cardoso, Vitor; Fender, Rob P.; Fromm, Christian M.; Galison, Peter; Gómez, José L.; et al (June 2023, Galaxies)

   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. 

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3. How Spatially Resolved Polarimetry Informs Black Hole Accretion Flow Models

   https://doi.org/10.3390/galaxies11010005  

   Ricarte, Angelo; Johnson, Michael D.; Kovalev, Yuri Y.; Palumbo, Daniel C.; Emami, Razieh (February 2023, Galaxies)

   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. 

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4. The Role of the Large Millimeter Telescope in Black Hole Science with the Next-Generation Event Horizon Telescope

   https://doi.org/10.3390/galaxies11010002  

   Bustamante, Sandra; Blackburn, Lindy; Narayanan, Gopal; Schloerb, F. Peter; Hughes, David (February 2023, Galaxies)

   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. 

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5. Bridging Scales: Modeling Suppressed Bondi Accretion on Black Holes and Its Impact on Galaxy Growth

   https://doi.org/10.3847/1538-4357/ae47fd  

   Porras-Valverde, Antonio J; Natarajan, Priyamvada; Ricarte, Angelo; Su, Kung-Yi; Cho_조, Hyerin 혜린; Narayan, Ramesh; Prather, Ben S (March 2026, The Astrophysical Journal)

   Abstract The accretion and feedback processes governing supermassive black hole (SMBH) growth span an enormous range of spatial scales, from the Event Horizon to the circumgalactic medium. Recent general relativistic magnetohydrodynamic (GRMHD) simulations demonstrate that strong magnetic fields can substantially suppress gas accretion onto black holes. These simulations show that magnetic fields create magnetically arrested disk states, reducing inflow rates by up to 2 orders of magnitude relative to classical predictions. We incorporate this magnetic suppression prescription from recent GRMHD studies into DarkSage, a semianalytic model that tracks SMBH and galaxy coevolution over cosmic time. Implementing the suppression across different accretion rate regimes, we explore its impact on the distribution of black hole masses, stellar masses in galaxies, and active galactic nucleus (AGN) luminosities. We find that restricting suppression to sub-Eddington accretors (f_Edd < 3 × 10⁻³) and rescaling AGN feedback efficiencies gives simultaneous agreement with the observed local distributions of both galaxy and black hole masses. At early cosmic times (z >  6), super-Eddington growth episodes dominate in our model, reproducing the high number densities of luminous AGN recently discovered by the James Webb Space Telescope. Our results highlight the critical sensitivity of galaxy assembly to the coupling between small-scale accretion physics and large-scale feedback regulation. Magnetic suppression of hot gas accretion can reconcile low-redshift constraints while preserving the rapid black hole growth required at early cosmic epochs, thereby providing a physically motivated bridge between horizon-scale GRMHD simulations and cosmological galaxy-formation models. 

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