Alexandru Lupsasca

Two papers sit at 213 citations each and they do opposite halves of one job. 'Lensing by Kerr Black Holes' works out the analytic theory, the three parameters that govern how each successive image of a source is demagnified, rotated and delayed. 'The Shape of the Black Hole Photon Ring' turns that theory into an experiment by showing the ring's shape barely depends on the emitting plasma. Underneath both sits 'The Null Geodesics of the Kerr Exterior' at 129 citations, the explicit elliptic-function solution that other groups now reuse as their reference case. Polarimetry is the fourth line, starting from the self-similar polarization pattern of the photon ring in 2020 and running into your current work on what horizon polarization says about where a black hole's energy is going.

The heaviest citers are people asking whether the object is Kerr at all. Vagnozzi and colleagues run your ring-size logic across more than fifty alternative spacetimes at 645 citations, and the EHT collaboration's own metric test on Sgr A* sits just behind at 613. Below those, a long tail of modified-gravity shadow papers treats the analytic Kerr geodesics as the reference case they measure deviations against. The 2026 citers keep that shape: a non-singular black hole review, a study of the vortical geodesics that thread both Kerr horizons, image calculations for non-minimally coupled black holes, and strong-deflection formulas extended from photons to massive particles. The polarimetry line landed somewhere more observational, with the EHT's ring-asymmetry analysis of M87* using spin constraints to separate competing jet-launching mechanisms.

When a paper cites you but we do not hold its full text, we flag it, so you can tell first-hand sources from second-hand mentions.

Andrew Strominger is the close collaborator pulling hardest in his own direction. You share 12 papers, but his output is 200 hep-th papers against 62 in gr-qc, and his densest ties run to Kapec, Wei Song and Raclariu rather than to anyone with a telescope. Samuel Gralla is the mirror image: 14 shared papers and nearly the same category ordering as yours, with his own network running through Wald, Zimmerman and Jacobson in classical relativity. The third corner is the imaging group, Johnson, Chael, Wong, Quataert and Cárdenas-Avendaño, which is where your recent output has concentrated and where the network opens out the furthest, since Michael Johnson's own top collaborators are the EHT core. Berens and Gravely sit on a fourth thread of their own, the Kerr metric-reconstruction papers.

Four researchers keep turning up next to your current directions, none at an institution you have held and none with a paper co-authored with you. Ben Achour is the closest fit, working both the beyond-Kerr photon ring and the analytic magnetosphere at once from the Lyon quantum gravity side. Cano comes at the near-extremal spectrum through effective field theory. Figueiredo brings kinetic plasma simulations to the tilted-field configurations your analytic work sets aside, and Tamar is building out the observational side of ring polarimetry.

The last 90 days have been about turning the photon ring from a prediction into a measurement plan, and about what stands in the way. Hioki and colleagues show a fragment of the critical curve is enough to fix spin and inclination. Wong and collaborators review horizon-scale polarimetry and conclude the current data pins down field geometry much better than spin. On the hardware side, the constraints are getting specific: which space clocks hold coherence at 345 GHz, which supermassive black holes come into range on an Earth-Moon baseline, where BHEX sits among the other space interferometry concepts. The theory side has stayed busy with exact WKB treatments of the extremal quasinormal spectrum and hidden conformal symmetry in modified-gravity Kerr.