Volume 618, October 2018
|Number of page(s)||15|
|Section||Letters to the Editor|
|Published online||31 October 2018|
Letter to the Editor
Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA*⋆
Max Planck Institute for Extraterrestrial Physics(MPE), Giessenbachstr.1, 85748 Garching, Germany
2 LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
3 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
4 1st Institute of Physics, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
5 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
6 Universidade de Lisboa – Faculdade de Ciências, Campo Grande, 1749-016, Lisboa, Portugal
7 Faculdade de Engenharia, Universidade do Porto, rua Dr. Roberto Frias, 4200-465 Porto, Portugal
8 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
9 European Southern Observatory, Casilla 19001, Santiago 19, Chile
10 Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
11 Departments of Physics and Astronomy, Le Conte Hall, University of California, Berkeley, CA 94720, USA
12 School of Physics and Astronomy„ Tel Aviv University, Tel Aviv 69978, Israel
13 Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
14 CENTRA – Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal
15 Center for Computational Astrophysics, Flatiron Institute, 162 5th Ave., New York, NY 10010, USA
Accepted: 5 October 2018
We report the detection of continuous positional and polarization changes of the compact source SgrA* in high states (“flares”) of its variable near-infrared emission with the near-infrared GRAVITY-Very Large Telescope Interferometer (VLTI) beam-combining instrument. In three prominent bright flares, the position centroids exhibit clockwise looped motion on the sky, on scales of typically 150 μas over a few tens of minutes, corresponding to about 30% the speed of light. At the same time, the flares exhibit continuous rotation of the polarization angle, with about the same 45(±15) min period as that of the centroid motions. Modelling with relativistic ray tracing shows that these findings are all consistent with a near face-on, circular orbit of a compact polarized “hot spot” of infrared synchrotron emission at approximately six to ten times the gravitational radius of a black hole of 4 million solar masses. This corresponds to the region just outside the innermost, stable, prograde circular orbit (ISCO) of a Schwarzschild–Kerr black hole, or near the retrograde ISCO of a highly spun-up Kerr hole. The polarization signature is consistent with orbital motion in a strong poloidal magnetic field.
Key words: Galaxy: center / black hole physics / gravitation / relativistic processes
The data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/618/L10
GRAVITY is developed in a collaboration by the Max Planck Institute for Extraterrestrial Physics, LESIA of Paris Observatory/Université PSL/CNRS/Sorbonne Université/Univ. Paris Diderot/Sorbonne Paris Cité, IPAG of Université Grenoble Alpes/CNRS, the Max Planck Institute for Astronomy, the University of Cologne, the CENTRA – Centro de Astrofísica e Gravitação, and the European Southern Observatory.
© ESO 2018
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