Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem1. This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very-long-baseline interferometry that has thus far been able to probe the structure of the jet acceleration and collimation region in only two sources2,3. Here, we report observations of 3C84 (NGC 1275)—the central galaxy of the Perseus cluster—made with an interferometric array including the orbiting radio telescope of the RadioAstron4 mission. The data transversely resolve the edge-brightened jet in 3C84 only 30 μas from the core, which is ten times closer to the central engine than was possible in previous ground-based observations5 and allows us to measure the jet collimation profile from ~102 to ~104 gravitational radii (rg) from the black hole. The previously found5, almost cylindrical jet profile on scales larger than a few thousand rg is seen to continue at least down to a few hundred rg from the black hole, and we find a broad jet with a transverse radius of 250 rg at only 350 rg from the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales 102rg or it is launched from the accretion disk.

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We thank E. Ros for useful comments on the manuscript. The RadioAstron project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the State Space Corporation ROSCOSMOS, in collaboration with partner organizations in Russia and other countries. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities. The European VLBI Network is a joint facility of independent European, African, Asian and North American radio astronomy institutes. The KVN is a facility operated by the Korea Astronomy and Space Science Institute. The KVN operations are supported by the Korea Research Environment Open NETwork, which is managed and operated by the Korea Institute of Science and Technology Information. This work was partially supported by the National Research Council of Science and Technology, granted by the International Joint Research Program (EU-16-001). This research is based on observations correlated at the Bonn Correlator, jointly operated by the Max-Planck-Institut für Radioastronomie and the Federal Agency for Cartography and Geodesy. T.S. was funded by the Academy of Finland projects 274477 and 284495. Y.Y.K., M.M.L., K.V.S. and P.A.V. were supported by the Russian Science Foundation (project 16-12-10481). S.-S.L. was supported by a National Research Foundation of Korea grant funded by the Korean government (MSIP; number 987 NRF-2016R1C1B2006697).

Author information


  1. Dipartimento di Fisica e Astronomia, Università di Bologna, Bologna, Italy

    • G. Giovannini
    • , F. D’Ammando
    •  & R. Lico
  2. Istituto di Radio Astronomia, INAF, Bologna, Italy

    • G. Giovannini
    • , M. Orienti
    • , M. Giroletti
    • , G. Bruni
    • , F. D’Ammando
    •  & R. Lico
  3. Aalto University Department of Electronics and Nanoengineering, Espoo, Finland

    • T. Savolainen
  4. Aalto University Metsähovi Radio Observatory, Kylmälä, Finland

    • T. Savolainen
  5. Max-Planck-Institut für Radioastronomie, Bonn, Germany

    • T. Savolainen
    • , G. Bruni
    • , Y. Y. Kovalev
    • , T. P. Krichbaum
    • , A. P. Lobanov
    •  & J. A. Zensus
  6. Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan

    • M. Nakamura
  7. National Astronomical Observatory of Japan, Osawa, Tokyo, Japan

    • H. Nagai
  8. Kogakuin University, Academic Support Center, Tokyo, Japan

    • M. Kino
  9. Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, Tokyo, Japan

    • M. Kino
    • , K. Hada
    •  & M. Honma
  10. Istituto di Astrofisica e Planetologia Spaziali, INAF, Roma, Italy

    • G. Bruni
  11. Astro Space Center of Lebedev Physical Institute, Moscow, Russia

    • Y. Y. Kovalev
    • , M. M. Lisakov
    • , K. V. Sokolovsky
    •  & P. A. Voitsik
  12. Moscow Institute of Physics and Technology, Moscow, Russia

    • Y. Y. Kovalev
    •  & L. Petrov
  13. Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany

    • J. M. Anderson
  14. Korea Astronomy and Space Science Institute, Yuseong-gu, Daejeon, Korea

    • J. Hodgson
    • , S.-S. Lee
    •  & B. W. Sohn
  15. Korea University of Science and Technology, Yuseong-gu, Daejeon, Korea

    • S.-S. Lee
    •  & B. W. Sohn
  16. Astrogeo Center, Falls Church, VA, USA

    • L. Petrov
  17. Department of Astronomy, Yonsei University, Seoul, Korea

    • B. W. Sohn
  18. IAASARS, National Observatory of Athens, Penteli, Greece

    • K. V. Sokolovsky
  19. Sternberg Astronomical Institute, Moscow State University, Moscow, Russia

    • K. V. Sokolovsky
  20. Curtin Institute of Radio Astronomy, Curtin University, Bentley, Australia

    • S. Tingay


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G.G., T.S. and M.O. coordinated the research, carried out the image analysis and wrote the manuscript. T.S., Y.Y.K., K.V.S., S.-S.L., B.W.S. and J.A.Z. planned and organized the space-VLBI imaging experiment, including the ground array. G.B. correlated the VLBI data with help from P.A.V., using the software tools developed by J.M.A. and L.P. Correlated VLBI data were calibrated by T.S. with contributions from M.M.L., while G.G., T.S., M.O. and Y.Y.K. imaged the data. The modelling was carried out by M.N., H.N., M.K. and M.G. All authors contributed to discussion of the data and its interpretation, and commented on the manuscript. T.S. is the Principal Investigator of the RadioAstron Nearby AGN Key Science Program.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to G. Giovannini or T. Savolainen.

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