Spatially resolved polarization swings in the supermassive binary black hole candidate OJ 287 with first Event Horizon Telescope observations
Journal article, 2026
We present the first Event Horizon Telescope 1.3 mm observations of the supermassive binary black hole candidate OJ 287. The observations achieved an unprecedented angular resolution of 18 µas and reveal significant structural and polarization variability over just five days, marking the shortest timescale on which such changes have been directly imaged in this source. The inner jet exhibits a twisted ridgeline structure, with features displaying apparent superluminal motions up to about 22 c. The linear polarization maps reveal three main polarized features whose electric-vector position angles (EVPAs) change substantially over the time span of our observations, including a component with a radial polarization consistent with being produced by a recollimation shock. Most notably, we directly resolved two innermost jet components whose EVPAs rotate in opposite directions. The faster component, moving at 2.4 ± 0.9 µas/day (17.4 ± 6.5 c), exhibits counterclockwise EVPA swings of roughly 3.7◦ per day, while the slower component, with a proper motion of 1.4 ± 0.3 µas/day (10.2 ± 2.2 c), rotates clockwise at approximately 2.5◦ per day. Previous studies inferred helical magnetic fields in AGN jets from time-resolved or integrated polarization variability but lacked the angular resolution to directly image this effect. Our results provide spatially resolved evidence that a helical magnetic field threads the jet’s collimation and acceleration zone, ruling out models based on the superposition of unresolved components. Our analysis suggests that propagating shocks interact with a Kelvin-Helmholtz plasma instability, illuminating different phases of the helical magnetic field and producing the observed polarization spatial and temporal variability. Moreover, our model naturally accounts for the more rapid polarization rotation observed in the faster moving component. Our model predicts even more rapid swings in polarization, which could be tested with future observations featuring a more densely sampled time coverage.
instabilities
black hole physics
radiation mechanisms: non-thermal
galaxies: individual: OJ 287
galaxies: active
techniques: interferometric
Author
J. L. Gomez
Spanish National Research Council (CSIC)
I. Cho
Yonsei University
Korea Astronomy and Space Science Institute
Spanish National Research Council (CSIC)
E. Traianou
Max Planck Society
Spanish National Research Council (CSIC)
T.P. Krichbaum
Max Planck Society
G. Y. Zhao
Spanish National Research Council (CSIC)
Max Planck Society
R. Lico
Spanish National Research Council (CSIC)
Istituto di Radioastronomia
Antonio Fuentes
Spanish National Research Council (CSIC)
Marianna Foschi
Spanish National Research Council (CSIC)
Rohan Dahale
Spanish National Research Council (CSIC)
Boris Georgiev
University of Arizona
Kotaro Moriyama
National Astronomical Observatory of Japan
Goethe University Frankfurt
M. Wielgus
Spanish National Research Council (CSIC)
R. Gold
University of Southern Denmark
Heidelberg University
Institut für Theoretische Physik Heidelberg
Dominic W. Pesce
Harvard University
Harvard-Smithsonian Center for Astrophysics
Hendrik Müller
Max Planck Society
S.G. Jorstad
Boston University
Teresa Toscano
Spanish National Research Council (CSIC)
J. Röder
Spanish National Research Council (CSIC)
José M. Martí
Universitat de Valencia
M. Perucho
Universitat de Valencia
Yuri Y. Kovalev
Max Planck Society
S. Komossa
Max Planck Society
Achamveedu Gopakumar
Tata Institute of Fundamental Research
M. J. Valtonen
Tuorla Observatory
Gabriele Bruni
Istituto nazionale di astrofisica (INAF)
S. Chandra
Physical Research Laboratory
Kazunori Akiyama
National Astronomical Observatory of Japan
Harvard University
Massachusetts Institute of Technology (MIT)
E. Albentosa-Ruiz
Universitat de Valencia
Antxon Alberdi
Spanish National Research Council (CSIC)
Walter Alef
Max Planck Society
Juan-Carlos Algaba
University of Malaya
Richard Anantua
Harvard-Smithsonian Center for Astrophysics
Rice University
Harvard University
University of Texas
K. Asada
Academia Sinica
R. Azulay
Max Planck Society
Universitat de Valencia
U. Bach
Max Planck Society
Anne-Kathrin Baczko
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Max Planck Society
David Ball
University of Arizona
Mislav Baloković
Yale University
Bidisha Bandyopadhyay
University of Concepcion
John Barrett
Massachusetts Institute of Technology (MIT)
M. Bauböck
Grainger College of Engineering
Bradford A. Benson
University of Chicago
Fermi National Accelerator Laboratory
Dan Bintley
East Asian Observatory
James Clerk Maxwell Telescope
Lindy Blackburn
Harvard-Smithsonian Center for Astrophysics
Harvard University
R. Blundell
Harvard-Smithsonian Center for Astrophysics
K. L. Bouman
California Institute of Technology (Caltech)
G. C. Bower
East Asian Observatory
University of Hawaii
James Clerk Maxwell Telescope
Academia Sinica
M. Bremer
Institut de Radioastronomie Millimétrique (IRAM)
Roger Brissenden
Harvard-Smithsonian Center for Astrophysics
Harvard University
Silke Britzen
Max Planck Society
Avery E. Broderick
Perimeter Institute for Theoretical Physics
University of Waterloo
D. Broguière
Institut de Radioastronomie Millimétrique (IRAM)
Thomas Bronzwaer
Radboud University
Sandra Bustamente
University of Massachusetts
Douglas Ferreira Carlos
University of Sao Paulo (USP)
J. E. Carlstrom
University of Chicago
The Enrico Fermi Institute
A. Chael
Princeton University
Chi Kwan Chan
University of Arizona
Dominic O. Chang
Harvard-Smithsonian Center for Astrophysics
Harvard University
Koushik Chatterjee
Harvard University
Harvard-Smithsonian Center for Astrophysics
S. Chatterjee
Cornell University
Ming Tang Chen
Academia Sinica
Yongjun Chen
Chinese Academy of Sciences
X. P. Cheng
Korea Astronomy and Space Science Institute
Pierre Christian
WattTime
Nicholas S. Conroy
Harvard-Smithsonian Center for Astrophysics
University of Illinois
John Conway
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Thomas M. Crawford
University of Chicago
G. Crew
Massachusetts Institute of Technology (MIT)
Alejandro Cruz-Osorio
Universidad Nacional Autónoma de México
Goethe University Frankfurt
Yuzhu Cui
Huazhong Normal University
Brandon Curd
Harvard-Smithsonian Center for Astrophysics
Harvard University
University of Texas
Jordy Davelaar
Princeton University
Mariafelicia De Laurentis
National Institute for Nuclear Physics
University of Naples Federico II
R. P. Deane
University of Pretoria
University of Witwatersrand
Rhodes University
Jessica Dempsey
James Clerk Maxwell Telescope
Netherlands Institute for Radio Astronomy (ASTRON)
East Asian Observatory
Gregory Desvignes
Max Planck Society
Paris Observatory
Jason Dexter
JILA
Vedant Dhruv
Grainger College of Engineering
Indu K. Dihingia
Shanghai Jiao Tong University
S. Doeleman
Harvard University
Harvard-Smithsonian Center for Astrophysics
Sergio A. Dzib
Max Planck Society
Ralph P. Eatough
Chinese Academy of Sciences
Max Planck Society
Razieh Emami
Harvard-Smithsonian Center for Astrophysics
H.D. Falcke
Radboud University
Joseph R. Farah
University of California
Las Cumbres Observatory Global Telescope Network
V. Fish
Massachusetts Institute of Technology (MIT)
E. Fomalont
National Radio Astronomy Observatory
H. Alyson Ford
University of Arizona
R. Fraga-Encinas
Radboud University
William T. Freeman
Massachusetts Institute of Technology (MIT)
Google Inc.
P. Friberg
James Clerk Maxwell Telescope
East Asian Observatory
Christian M. Fromm
University of Würzburg
Max Planck Society
Goethe University Frankfurt
Peter Galison
Harvard University
Charles F. Gammie
Grainger College of Engineering
University of Illinois
Roberto Garcia
Institut de Radioastronomie Millimétrique (IRAM)
Olivier Gentaz
Institut de Radioastronomie Millimétrique (IRAM)
Gertie Geertsema
Royal Netherlands Meteorological Institute
C. Goddi
University of Cagliari
University of Sao Paulo (USP)
National Institute for Nuclear Physics
Istituto nazionale di astrofisica (INAF)
Arturo I. Gómez-Ruiz
National Council for Science and Technology Mexico
National Institute of Astrophysics, Optics and Electronics
Michael Lindqvist
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Minfeng Gu
Chinese Academy of Sciences
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 705 A23RadioNet 4
European Commission (EC) (EC/H2020/730562), 2017-01-01 -- 2020-12-31.
Onsala space observatory infrastructure
Swedish Research Council (VR) (2017-00648), 2018-01-01 -- 2021-12-31.
Infrastructure
Onsala Space Observatory
Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1051/0004-6361/202555831