A wide and collimated radio jet in 3C84 on the scale of a few hundred gravitational radii

• Published in: Nature astronomy Vol. 2; no. 6; pp. 472 - 477
• Main Authors: Giovannini, G., Savolainen, T., Orienti, M., Nakamura, M., Nagai, H., Kino, M., Giroletti, M., Hada, K., Bruni, G., Kovalev, Y. Y., Anderson, J. M., D’Ammando, F., Hodgson, J., Honma, M., Krichbaum, T. P., Lee, S.-S., Lico, R., Lisakov, M. M., Lobanov, A. P., Petrov, L., Sohn, B. W., Sokolovsky, K. V., Voitsik, P. A., Zensus, J. A., Tingay, S.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2018; Nature Publishing Group
• Subjects: 639/33; 639/33/34/863; 639/33/34/864; Accretion; Accretion disks; Astronomy; Astrophysics and Cosmology; Interferometry; Letter; Physics; Physics and Astronomy
• ISSN: 2397-3366; 2397-3366
• DOI: 10.1038/s41550-018-0431-2

Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem 1 . 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 sources 2 , 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 RadioAstron 4 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 observations 5 and allows us to measure the jet collimation profile from ~10 2 to ~10 4 gravitational radii ( r g ) from the black hole. The previously found 5 , almost cylindrical jet profile on scales larger than a few thousand r g is seen to continue at least down to a few hundred r g from the black hole, and we find a broad jet with a transverse radius of ≳ 250  r g at only 350  r g from the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales ≲10 2   r g or it is launched from the accretion disk. Interferometric observations of 3C84 reveal a broad cylindrical jet a few hundred gravitational radii from the black hole, implying that the jet either undergoes a rapid lateral expansion on even smaller scales or is launched from the accretion disk.