Chronological feed of everything captured from Feryal.
Using three epochs of Event Horizon Telescope (EHT) observations, the EHT Collaboration compares the observed distribution of ring brightness asymmetry amplitudes in M87* against GRMHD simulation libraries spanning a range of black hole spins. For strongly magnetized (MAD) accretion models, the data marginally disfavor low spin magnitudes (|a*| ≲ 0.2), consistent with the Blandford-Znajek jet-launching mechanism requiring nonzero spin. The study also quantifies how additional EHT epochs would tighten spin constraints, with implications for distinguishing jet-launching mechanisms and black hole growth histories.
The Event Horizon Telescope's long baselines resolve compact black hole structure but are blind to extended, large-scale jet emission — a known flux recovery problem. This paper introduces a technique exploiting "trivial" closure phases from nearly co-located EHT station pairs, which become non-zero in the presence of multi-scale brightness structure, to measure image moments (centroid, higher-order) with minimal model assumptions. Applied to 2017–2021 EHT observations of M87*, the method detects a preference for extended jet-aligned emission and localizes the source centroid ~1 mas northwest of the compact ring, consistent with lower-frequency jet morphology.
This paper extends robust optimization theory to a nonsmooth, nonconvex function class where the objective is expressed as a Difference of Tangentially Convex (DTC) functions under data uncertainty. The authors develop nonsmooth calculus rules that connect Fréchet and limiting subdifferentials for a class of maximum functions to the tangential subdifferential of their component functions. Using these tools, they derive optimality conditions for DTC problems under generalized constraint qualifications, broadening the tractable frontier of nonconvex robust optimization beyond DC (difference of convex) programming.
ALMA full-polarization observations of Sagittarius A* during the 2018 EHT campaign reveal a striking asymmetry: total intensity variability is low (<10%), while linear and circular polarization variability reach ~30% and ~50%, respectively — implying polarized emission originates from a spatially and physically distinct, coherent structure. A notable April 24 event, coinciding with a Chandra X-ray flare, showed near-simultaneous X-ray and millimeter peaks with an inter-band delay in polarized intensity and coherent polarization loop evolution. This simultaneity contradicts standard delayed synchrotron cooling models and instead favors continuous energy injection into an optically thin emission region. The results provide new observational constraints for accretion and plasma models near the Galactic Center black hole.