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The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87's large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.
|Number of pages||31|
|Journal||Astrophysical Journal Letters|
|Publication status||Published - 10 Apr 2019|
|MoE publication type||A1 Journal article-refereed|
- accretion, accretion disks
- black hole physics
- galaxies: individual (M87)
- galaxies: jets
- magnetohydrodynamics (MHD)
- techniques: high angular resolution
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- 1 Finished
Physics of Black Hole-Powered Jets
Savolainen, T. & Chamani Velasco, W.
01/09/2017 → 31/08/2019
Project: Academy of Finland: Other research funding
Metsähovi Radio Observatory
Joni Tammi (Manager)School of Electrical Engineering