Collimation of the Relativistic Jet in the Quasar 3C 273

Hiroki Okino*, Kazunori Akiyama, Keiichi Asada, José L. Gómez, Kazuhiro Hada, Mareki Honma, Thomas P. Krichbaum, Motoki Kino, Hiroshi Nagai, Uwe Bach, Lindy Blackburn, Katherine L. Bouman, Andrew Chael, Geoffrey B. Crew, Sheperd S. Doeleman, Vincent L. Fish, Ciriaco Goddi, Sara Issaoun, Michael D. Johnson, Svetlana JorstadShoko Koyama, Colin J. Lonsdale, Ru Sen Lu, Ivan Martí-Vidal, Lynn D. Matthews, Yosuke Mizuno, Kotaro Moriyama, Masanori Nakamura, Hung Yi Pu, Eduardo Ros, Tuomas Savolainen, Fumie Tazaki, Jan Wagner, Maciek Wielgus, Anton Zensus

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


The collimation of relativistic jets launched from the vicinity of supermassive black holes (SMBHs) at the centers of active galactic nuclei (AGNs) is one of the key questions to understand the nature of AGN jets. However, little is known about the detailed jet structure for AGN like quasars since very high angular resolutions are required to resolve these objects. We present very long baseline interferometry (VLBI) observations of the archetypical quasar 3C 273 at 86 GHz, performed with the Global Millimeter VLBI Array, for the first time including the Atacama Large Millimeter/submillimeter Array. Our observations achieve a high angular resolution down to ∼60 μas, resolving the innermost part of the jet ever on scales of ∼105 Schwarzschild radii. Our observations, including close-in-time High Sensitivity Array observations of 3C 273 at 15, 22, and 43 GHz, suggest that the inner jet collimates parabolically, while the outer jet expands conically, similar to jets from other nearby low-luminosity AGNs. We discovered the jet collimation break around 107 Schwarzschild radii, providing the first compelling evidence for structural transition in a quasar jet. The location of the collimation break for 3C 273 is farther downstream from the sphere of gravitational influence (SGI) from the central SMBH. With the results for other AGN jets, our results show that the end of the collimation zone in AGN jets is governed not only by the SGI of the SMBH but also by the more diverse properties of the central nuclei.

Original languageEnglish
Article number65
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2022 Nov 1

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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