Patrick M. Koch

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.

Context . Accretion streamers connected to protostellar disks and/or envelopes are thought to transport material across several thousand of au. Whether the motions of the gas comprising these streamers are dominated by gravity, large scale external turbulence or the action of magnetic fields is still under scrutiny. Aims . The aim of this work is to understand the role of the magnetic fields in the star-formation processes, in particular the role that magnetic forces have in potentially leading flows of gas and accretion onto the envelopes and disks orbiting protostars. Methods . First, we try to identify large-scale accretion streamers toward the high-mass Young Stellar Object GGD 27–MM1 and fit their trajectories using the so-called Mendoza model, a modification of the classical model of pure gravitational infalling motion of fluid particles in a potential well. Second, we estimate the strength of the magnetic field associated with the streamers. Then, we determine whether the streamers are dominated by magnetic or centrifugal forces. Results . Inspecting the Atacama Large Millimeter/submillimeter Array (ALMA) H ₂ CO cube we were able to identify four accretion streamers spreading up to ∼7000 au and fit their trajectories in the position-position-velocity space. The polarized continuum emission reveals a good alignment of the magnetic field and the trajectory of the streamers. Using the Davis-Chandrasekhar-Fermi (DCF) method, we derive estimates for the magnetic field strength, find that the streamers are sub-Alfvénic, and discuss (after estimating energy terms for turbulence, ordered motions, magnetic forces, and gravity) a possible qualitative scenario in which, the gravitational well of the GGD 27–MM1 protostar dominates streamer gas motions over turbulence and magnetic forces at distances of ∼3000 au.

Our understanding of magnetic fields (B-fields) in massive star formation remains incomplete. Linear polarized emission from magnetically aligned dust grains provides a good way to map the morphology of the B-field on the plane of the sky. Here, we present the 1.2 mm full polarization observation of W33 A, a massive star-forming region at 2.4 kpc, obtained with the Atacama Large Mil-limeter/Submillimeter Array (ALMA) to achieve an angular resolution of ∼0″.3 (∼730 au). W33 A is resolved into 20 dense cores and nine filaments. It reveals various B-field structures, including two perpendicular large-scale components oriented northwest–southeast (NW–SE) and northeast–southwest (NE–SW), as well as two local distinct features toward the millimeter peaks MM1 and MM2. The NW–SE component could be shaped by a molecular outflow. The NE–SW one is remarkably coherent along the main filamentary structures (F1, F-Main, Tail), all with trans-Alfvénic turbulence. In F-Main, the line mass exceeds the turbulent critical limits, so magnetic support is required to prevent radial collapse and suppress local fragmentation. In F1 and Tail, turbulence is sufficient to support gravity, although B-fields can potentially provide additional support. Toward MM1, the fields follow a spiral-like, infalling streamer traced by CH ₃ CN; the inferred trans-Alfvénic turbulence in the accreting material indicates magnetic damping of turbulence and a magnetically regulated, laminar accretion flow that continues to feed the core. Toward MM2, the field exhibits an hourglass geometry described by parabolic curves. Two independent methods yield a consistently strong field strength of ∼8.1 ± 1.9 mG. The virial analysis shows that the B-field can add 25% (75% from turbulence) support against gravity but is not by itself sufficient to halt collapse. Our study shows that within one protocluster, B-fields can both help stabilize gas filament against local fragmentation to facilitate mass accretion and delay gravitational collapse. The distinct evolutionary stages of MM1 and MM2 highlight the dynamic importance of B-fields in massive star formation.

Magnetic fields play a crucial yet complex role in star formation, while their connection between large-scale filamentary clouds and small-scale young stellar objects remains poorly understood. We present new continuum polarization observations from the JCMT, ACA, and ALMA that provide continuous magnetic field measurements from ∼5 pc down to ∼4000 au, tracing for the first time the evolution of field morphology seamlessly across all key scales within a massive star-forming system. Our polarization maps reveal multiple U-shaped magnetic field structures pointing toward the central protocluster, aligned with accreting filaments from parsec- to subparsec-scales and converging at the compact center. This morphology suggests an environment of colliding flows that drag magnetic fields and trigger massive protocluster formation. On ∼4000 au scales, we identify compact U-shaped fields likely guiding the kinematics of streamers accreting onto dense cores. The increasing curvature of these U-shaped patterns is a direct measure of a growing magnetic field tension force, implying a magnetic field strength scaling index of 0.50 ± 0.10. These results indicate that the field, possibly enhanced by large-scale flow collisions, becomes strong enough to regulate star formation, linking parsec-scale colliding flows, a subparsec hub–filament system, and the triggering of massive star formation.

The role of magnetic fields in the observed inefficiency of star formation in Galactic molecular clouds is a widely debated topic, with the past decade seeing an explosion of observational characterisation of magnetic fields in star-forming regions. However, few have studied the spatial evolution of magnetic fields from entire molecular clouds down to parsec-size cluster-forming clumps. In this work, the plane-of-sky morphology of the magnetic fields of eight infrared dark clumps and their parent molecular clouds are derived from Planck and JCMT POL-2 polarisation data (including some from the BISTRO survey). We also use this data to test multiple methods of calculating B-field strengths. Our study shows that the morphologies of magnetic fields in clumps and their parent molecular clouds systematically, and significantly, differ, supported by a line-of-sight correction of the cloud-scale magnetic fields using the velocity gradient technique. We find a strong correlation between gas velocity dispersion and the alignment of magnetic field lines with column density gradients from scales of tens of parsecs to a few parsecs. This correlation is clear evidence of a link between the kinematic properties of the gas and the dynamical importance of magnetic fields. Conversely, the higher magnetic field strengths we measure on cloud scale compared to clump scale contradict magnetic flux conservation and thus highlight the unreliability of such measurements. Altogether, our analysis supports a picture in which magnetic fields have little impact on the dynamical evolution of cluster-forming clumps but do play a role in providing support on larger scales.

Polarised dust emission observations are a valuable tool to infer the structure of the magnetic field, and the dispersion of polarization position angles may be used to estimate magnetic field strengths. A natural consequence of magnetodynamic turbulence is for the angular dispersion to have a length scale dependence, making the measurement of angular dispersion nontrivial. In this paper we present a study of parameterized, scale-dependent maps, focusing on the effect of pixel size and beam convolution on the measured angular dispersion when using the commonly employed unsharp-masking and structure function methods. We find that in all cases the measured angular dispersion is underestimated compared to the true value. The degree to which the measured angular dispersion is underestimated varies by factors of 1–10 when measured on scales of 1–3× the beam size and depends on the underlying structure of the polarization angle field. This suggests that currently derived magnetic field strengths using angular dispersions are chronically overestimated, potentially leading to an overly magnetically dominated view of star formation. We present a method to estimate a correction factor to account for this and apply it to JCMT Orion A OMC-1 observations. We find that the magnetic field in OMC-1 is predominately found to vary on scales much larger than the JCMT’s 14″ beam and has a rather low degree of unresolved dispersion, leading to a correction factor of only ∼1.6 for angular dispersion measured at a scale of 14″/0.028 pc.

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.

Context . High-mass stars and star clusters form from the fragmentation of massive dense clumps driven by gravity, turbulence, and magnetic fields. The extent to which each of these agents impacts the fragmentation depending on the clump mass, density, and evolutionary stage is still largely unknown. Aims . The ALMA evolutionary study of high-mass protocluster formation in the GALaxy (ALMAGAL) project, with ∼1000 clumps observed at ∼1000 au resolution, allows a statistically significant characterization of the fragmentation process over a large range of clump physical parameters and evolutionary stages. Our goal is to characterize where and how the dense cores revealed by ALMA are distributed in massive potentially cluster-forming clumps to trace how fragmentation is initially set and how it proceeds before gas dispersal due to stellar feedback. Methods . We characterized the spatial distribution of dense cores in the 514 ALMAGAL clumps that host at least four cores, using a set of quantitative descriptors that we evaluated against the clump bolometric luminosity-to-mass ratio, which we adopted as an indicator of the evolution of the system. We measured the separations between cores with the minimum spanning tree (MST) method, which we compared with the predictions of gravitational fragmentation from Jeans theory. We investigated whether cores have specific arrangements using the Q parameter or variations due to their masses with the mass segregation ratio, Λ _MSR . Results . ALMAGAL cores are distributed throughout the entire area of the clump, usually arranged in elliptical groups with an axis ratio e ∼2.2, although high values with e ≥ 5 are also observed. We found a single characteristic core separation per clump in ∼76% of cases, suggesting that multiple fragmentation lengths may be frequently present. Typical core separations are compatible with the clump-averaged thermal Jeans length, λ _J ^th . However, we found an additional population of cores, typical of low-fragmented and young clumps, which are on average more widely separated with l ≈ 3 × λ _J ^th . By stacking the distributions of the core separations in clumps of similar evolutionary stage, we also found that the separation decreases on average from l ∼22 000 au in younger systems to l ∼7000 au in more evolved ones. The ALMAGAL cores are typically distributed in fractal-type subclusters, while centrally concentrated patterns appear only at later stages, but we do not observe a progressive transition between these configurations with evolution. Finally, we also found 110 ALMAGAL systems with a signature of mass segregation, with an occurrence that increases with evolution.