Probing jet base emission of M87* with the 2021 Event Horizon Telescope observations
Journal article, 2026
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.
Black hole physics
Galaxies: individual: M 87*
Relativistic processes
Accretion, accretion disks
Galaxies: jets
Gravitation
Author
Saurabh
Max Planck Society
Hendrik Müller
National Radio Astronomy Observatory
S. von Fellenberg
Max Planck Society
Canadian Institute for Theoretical Astrophysics
Paul Tiede
Harvard University
Harvard-Smithsonian Center for Astrophysics
Michael Janssen
Radboud University
Max Planck Society
Lindy Blackburn
Harvard-Smithsonian Center for Astrophysics
Harvard University
Avery E. Broderick
University of Waterloo
Perimeter Institute for Theoretical Physics
Erandi Chavez
Harvard-Smithsonian Center for Astrophysics
Boris Georgiev
University of Arizona
T.P. Krichbaum
Max Planck Society
Kotaro Moriyama
Goethe University Frankfurt
National Astronomical Observatory of Japan
Dhanya G. Nair
Max Planck Society
Iniyan Natarajan
Harvard University
Harvard-Smithsonian Center for Astrophysics
Jongho Park
Kyung Hee University
Academia Sinica
Andrew Thomas West
University of Arizona
M. Wielgus
Spanish National Research Council (CSIC)
Kazunori Akiyama
Harvard University
Massachusetts Institute of Technology (MIT)
National Astronomical Observatory of Japan
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
University of Texas
Rice University
Harvard University
K. Asada
Kyung Hee University
R. Azulay
Universitat de Valencia
Max Planck Society
U. Bach
Max Planck Society
Anne-Kathrin Baczko
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
David Ball
University of Arizona
Mislav Baloković
Yale University
Bidisha Bandyopadhyay
University of Concepcion
John Barrett
Massachusetts Institute of Technology (MIT)
M. Bauböck
University of Illinois
Bradford A. Benson
Fermi National Accelerator Laboratory
University of Chicago
Dan Bintley
James Clerk Maxwell Telescope
East Asian Observatory
R. Blundell
Harvard-Smithsonian Center for Astrophysics
K. L. Bouman
California Institute of Technology (Caltech)
G. C. Bower
James Clerk Maxwell Telescope
Academia Sinica
East Asian Observatory
M. Bremer
Institut de Radioastronomie Millimétrique (IRAM)
Roger Brissenden
Harvard-Smithsonian Center for Astrophysics
Silke Britzen
Max Planck Society
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
A. Chael
Princeton University
Chi Kwan Chan
University of Arizona
Dominic O. Chang
Harvard-Smithsonian Center for Astrophysics
Harvard University
Koushik Chatterjee
Harvard University
University of Maryland
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
Paul Chichura
University of Chicago
I. Cho
Academia Sinica
Yonsei University
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
Spanish National Research Council (CSIC)
Alejandro Cruz-Osorio
Universidad Nacional Autónoma de México
Goethe University Frankfurt
Yuzhu Cui
Central China Normal University
Brandon Curd
Harvard-Smithsonian Center for Astrophysics
Harvard University
University of Malaya
Rohan Dahale
Academia Sinica
Jordy Davelaar
Princeton University
Mariafelicia De Laurentis
National Institute for Nuclear Physics
University of Naples Federico II
R. P. Deane
University of Witwatersrand
University of Pretoria
Rhodes University
Gregory Desvignes
Max Planck Society
Centre national de la recherche scientifique (CNRS)
Jason Dexter
University of Colorado
Vedant Dhruv
University of Illinois
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
Max Planck Society
Chinese Academy of Sciences
Razieh Emami
Harvard-Smithsonian Center for Astrophysics
H.D. Falcke
Radboud University
Joseph R. Farah
Las Cumbres Observatory Global Telescope Network
University of California
V. Fish
Spanish National Research Council (CSIC)
E. Fomalont
National Radio Astronomy Observatory
H.D. Falcke
Radboud University
Marianna Foschi
Academia Sinica
R. Fraga-Encinas
Radboud University
William T. Freeman
Massachusetts Institute of Technology (MIT)
Google Inc.
P. Friberg
East Asian Observatory
James Clerk Maxwell Telescope
Christian M. Fromm
Goethe University Frankfurt
Max Planck Society
University of Würzburg
Antonio Fuentes
Academia Sinica
Peter Galison
Harvard University
Charles F. Gammie
University of Illinois
Roberto Garcia
Institut de Radioastronomie Millimétrique (IRAM)
Olivier Gentaz
Institut de Radioastronomie Millimétrique (IRAM)
C. Goddi
National Institute for Nuclear Physics
University of Sao Paulo (USP)
University of Cagliari
R. Gold
Heidelberg University
University of Southern Denmark
Arturo I. Gómez-Ruiz
National Institute of Astrophysics, Optics and Electronics
J. L. Gomez
Academia Sinica
Minfeng Gu
Chinese Academy of Sciences
M. Gurwell
Harvard-Smithsonian Center for Astrophysics
K. Hada
National Astronomical Observatory of Japan
Nagoya University
Daryl Haggard
McGill University
R. Hesper
University of Groningen
Dirk Heumann
University of Arizona
Luis C. Ho
Peking University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 706 A27Subject Categories (SSIF 2025)
Fusion, Plasma and Space Physics
Astronomy, Astrophysics, and Cosmology
DOI
10.1051/0004-6361/202557022