2023-04-13 カリフォルニア大学バークレー校(UCB)
この発見により、ブラックホールの自転方向が決定でき、重力波の観測の解釈につながることが期待される。また、巨大楕円銀河の真の形状を決定することで、銀河やブラックホールの成長について理解を深めることができるという。
＜関連情報＞
- https://news.berkeley.edu/2023/04/13/3d-picture-of-galaxy-m87-helps-pin-down-mass-of-the-black-hole-at-its-core/
- https://iopscience.iop.org/article/10.3847/2041-8213/acbbcf
M87のケック望遠鏡による積分視野分光で、三軸銀河とブラックホール質量が判明 Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass
Emily R. Liepold, Chung-Pei Ma, and Jonelle L. Walsh
The Astrophysical Journal Letters Published 2023 March 15
DOI:10.3847/2041-8213/acbbcf
Abstract
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here, we present spatially resolved stellar kinematics of M87 over a two-dimensional 250” × 300” contiguous field covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope. From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis (connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy. Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine the black hole mass to be 
, where the second error indicates the systematic uncertainty associated with the distance to M87.
