Approaching the Schwarzschild Radius

Hada et al. report on high-sensitivity, high-resolution 86 GHz observations of the jet base in the radio galaxy M87, obtained by the Very Long Baseline Array in conjunction with the Green Bank Telescope. The resulting image has a dynamic range exceeding 1500 to 1, resolving and imaging a detailed jet structure to ∼10 Schwarzschild radii (R_s). The 86 GHz image confirms important jet features known at lower frequencies, a jet base with a wide opening angle, a limb-brightened intensity profile, a parabola-shape collimation profile, and a counter jet. The limb-brightened structure is already well developed at < 0.2 milli-arcsecond (< 28 R_s, projected) from the core, where the corresponding apparent opening angle becomes as wide as ~ 100 deg. The subsequent jet collimation near the black hole evolves in a complex manner: there is a constricted structure at tens of R_s from the core, where the jet cross section is locally shrinking. The authors suggest that external pressure support from the inner part of the radiatively inefficient accretion flow may be dynamically important in confining the footprint of the magnetized jet. The authors also present the first 86 GHz polarimetric experiment using VLBI for this source.

Image:  VLBA + GBT 86 GHz false-color total intensity image of the M87 jet. The image is produced by combining the visibility data over the two epochs on 11 & 26 February 2014. The restoring beam is shown in the bottom-right corner. The peak intensity is 500 mJy/beam, the off-source rms noise is 0.28 mJy/beam, where the resulting dynamic range is greater than 1500 to 1.

Science Team: Kazuhiro Hada (NAOJ, INAF), Motoki Kino (KASI), Akihiro Doi (JAEA), Hiroshi Nagai (NAOJ), Mareki Honma (NAOJ, SOKENDAI), Kazunori Akiyama (NAOJ, Tokyo), Fumie Tazaki (NAOJ), Rocco Lico (INAF, Bologna), Marcello Giroletti (INAF), Gabriele Giovannini (INAF, Bologna), Monica Orienti (INAF), and Yoshiaki Hagiwara (NAOJ, Tokyo).

Publication: High-sensitivity 86 GHz (3.5 mm) VLBI Observations of M87: Deep Imaging of the Jet Base at a Resolution of 10 Schwarzschild Radii, 2016, Astrophysical Journal, 817, 131.