George N. Wong

In 2026, the Event Horizon Telescope (EHT) carried out the first time-lapse monitoring campaign comprising a series of 18 observations of the 6.1 6 − 0.57 + 0.71 × 1 0 9 M ⊙ black hole at the center of M87 with a cadence of approximately twice per week over a few months, matched to the expected dynamical timescale. Here we present a first-look image from the campaign, reconstructed from a single four-minute scan obtained on 2026 April 3. The resulting image displays the now-familiar asymmetric ring morphology first revealed by the 2017 EHT observations and subsequently confirmed by observations obtained in 2018 and 2021. While representing only a very small subset of the full program, this image demonstrates a significant advance in the operational capabilities of the EHT. Through improvements in array operations, data transport and processing, the collaboration has reduced the interval between observation and imaging to only a few months, establishing the EHT as a facility capable of routinely undertaking time-domain studies of the dynamic universe at extremely high resolutions of ∼20 μ as.

Observations of active galactic nuclei have revealed a correlation between millimeter luminosity, X-ray luminosity, and mass, suggesting the emission in each of these bands is powered by a common source. Starting with a set of five general relativistic magnetohydrodynamic simulations with dynamically important magnetic fields, we perform ray-tracing calculations to produce spectra including synchrotron emission, bremsstrahlung emission, and Compton scattering. Our models with similar Eddington ratios to the objects for which the relationship was inferred naturally reproduce observations without tuning. Our lower Eddington ratio models depart from this relationship, likely attributable to an observational bias against extremely low accretion rates. We find that inverse Compton scattering dominates the production of X-rays over bremsstrahlung radiation in almost all models, and in all models consistent with the observed correlation. We find only a modest spin dependence in this relationship. This study demonstrates that a compact, hot accretion flow with dynamically important magnetic fields can naturally explain observed millimeter and X-ray properties in low-luminosity active galactic nuclei. Future work should explore the impacts of nonthermal electron populations, weaker magnetic fields, and radiative cooling.

The 2021 Event Horizon Telescope observations resolve the innermost jet region of the blazar 3C 279 with unprecedented detail. The reconstructed images consistently reveal a compact core elongated nearly orthogonal to the large-scale jet axis. This rarely observed morphology recurs across multiple epochs and from 22–230 GHz and is therefore intrinsic rather than an imaging artifact. Geometric model fitting identifies several components with apparent speeds up to β _app ∼ 10, requiring bulk Lorentz factors Γ ≳ 10.3 and constraining viewing angles to extremely small values (≲1°). Rest-frame brightness temperatures are systematically low ( T _B ∼ 10 ⁹ –10 ¹⁰ K), consistent with optically thin emission at 230 GHz. These results suggest that the jet bends toward the observer on sub-parsec scales, producing strong relativistic beaming. Possible drivers of the observed jet bending and temporal evolution include the jet’s interaction with the interstellar medium, kink or Kelvin-Helmholtz instabilities, magnetic reconnection near the horizon, or binary-induced precession. However, the current temporal coverage of VLBI data remains insufficient to distinguish between these mechanisms. Continued multifrequency VLBI monitoring will be essential to constraining the dynamics and geometry of the jet base in 3C 279.

Polarized images of a black hole encode the direction of electromagnetic energy flow near its event horizon. Measuring polarization from near-horizon emission can help determine whether this energy flow is powered by the accreting plasma or the black hole spin. Here we consider the linear polarization of synchrotron radiation emitted from the base of horizon-threading field lines in a time-stationary, axisymmetric, and degenerate Kerr magnetosphere with nonzero poloidal current. We show that the observed polarization pattern displays universal behavior: it is completely determined by the black hole spin and observer inclination and is independent of the magnetic-field geometry. We derive a simple analytic formula for this spin-dependent horizon polarization pattern. We find that this predicted pattern is also approached in time-averaged images from general relativistic magnetohydrodynamic simulations. Future observations with very-long-baseline interferometry at microarcsecond resolution could detect the trend of polarization toward the unique horizon value in M87*. Such observations may enable new measurements of black hole spin and provide evidence that magnetic field lines thread the horizon, a necessary condition for spin-energy extraction via the Blandford–Znajek process.

The angular momentum of a black hole, usually expressed in terms of a dimensionless “spin,” both shapes the strong-field spacetime and provides a reservoir of rotational energy that can be exchanged with surrounding plasma. Very long baseline interferometry (VLBI) has now begun to resolve polarized emission on event-horizon scales. We distinguish polarimetric signatures of spin arising primarily from photon propagation in the Kerr spacetime from those mediated by horizon-threading electromagnetic fields and magnetized plasma dynamics. We trace the inference from VLBI correlations through Stokes images and compact summary statistics to constraints on the source and, ultimately, on spin. Within this framework, we review diagnostics linked to horizon regularity and magnetic field winding, magnetically arrested accretion, electromagnetic energy extraction, jet-base and light-cylinder structure, and horizon and photon-ring polarization. Current Event Horizon Telescope observations constrain magnetic field geometry, variability, source orientation, magnetic flux state, and aspects of the disk–jet connection more robustly than they constrain spin magnitude or sense. Future observing and modeling programs should prioritize combinations of polarimetric diagnostics with complementary systematics and test whether a common spin-dependent interpretation is supported across independent data products and plausible source models.

Event Horizon Telescope (EHT) images of the supermassive black hole M87* depict an asymmetric ring of emission. General relativistic magnetohydrodynamic (GRMHD) models of M87* and its accretion disk predict that the amplitude and location of the ring’s peak brightness asymmetry should fluctuate due to turbulence in the source plasma. We compare the observed distribution of brightness asymmetry amplitudes to the simulated distribution in GRMHD models, across varying black hole spin a _* . We show that, for strongly magnetized (MAD) models, three epochs of EHT data marginally disfavor ∣ a _* ∣ ≲ 0.2. This is consistent with the Blandford–Znajek model for M87’s jet, which predicts that M87* should have nonzero spin. We show quantitatively how future observations could improve spin constraints and discuss how improved spin constraints could distinguish between differing jet-launching mechanisms and black hole growth scenarios.

We describe AthenaK : a new implementation of the Athena++ block-based adaptive mesh refinement framework using the Kokkos programming model. Finite volume methods for Newtonian, special relativistic, and general relativistic (GR) hydrodynamics and magnetohydrodynamics (MHD), and GR-radiation hydrodynamics and MHD, as well as a module for evolving Lagrangian tracer or charged test particles (e.g., cosmic rays) are implemented using the framework. In two companion papers, we describe (1) a new solver for the Einstein equations based on the Z4c formalism, and (2) a GRMHD solver in dynamical spacetimes also implemented using the framework, enabling new applications in numerical relativity. By adopting Kokkos , the code can be run on virtually any hardware, including CPUs, GPUs from multiple vendors, and emerging Advanced RISC Machine processors. AthenaK shows excellent performance and weak scaling, achieving over 1 billion cell updates per second for hydrodynamics in three dimensions on a single NVIDIA Grace Hopper processor. It does this with a typical parallel efficiency of 80% on 65,536 AMD GPUs on the OLCF Frontier system. Such performance portability enables AthenaK to leverage modern exascale computing systems for challenging applications in astrophysical fluid dynamics, numerical relativity, and multimessenger astrophysics.

We investigate the presence and spatial characteristics of the jet base emission in M87* at 230 GHz, enabled by the significantly enhanced ( u,v ) coverage in the 2021 Event Horizon Telescope (EHT) observations. The integration of the 12−m Kitt Peak Telescope (USA) and NOEMA (France) stations into the array introduces two critical intermediate-length baselines to SMT (USA) and IRAM 30−m (Spain), providing sensitivity to emission structures at spatial scales of ∼250 μas and ∼2500 μas (∼ 0.02 pc and ∼ 0.02 pc). Without these new baselines, previous EHT observations of the source in 2017 and 2018 lacked the capability to constrain emission on large scales, where a “missing flux” of order ∼1 Jy is expected to reside. To probe these scales, we analyzed closure phases–robust against station-based gain calibration errors–and model the jet base emission using a simple Gaussian component offset from the compact ring emission at spatial separations > 100 μas. Our analysis revealed a Gaussian feature centered at (ΔRA ≈ 320 μas, ΔDec. ≈ 60 μ as), projected separation of ≈ 5500 AU, with an estimated flux density of only ∼60 mJy, implying that most of the missing flux identified in previous EHT studies had to originate from different, larger scales. Brighter emission at the relevant spatial scales is firmly ruled out, and the data do not favor more complex models. This component aligns with the inferred position of the large-scale jet and is therefore physically consistent with the emission of the jet base. While our findings point to detectable jet base emission at 230 GHz, the limited coverage provided by only two intermediate baselines limits our ability to robustly reconstruct its morphology. Consequently, we treated the recovered Gaussian as an upper limit on the jet base flux density. Future EHT observations with expanded intermediate baseline coverage will be essential to constrain the structure and nature of this component with higher precision.