http://arxiv.org/abs/1908.10376
The first image of the black hole (BH) M87* obtained by the Event Horizon Telescope (EHT) has the shape of a crescent extending from the E to SWW position angles, while the observed direction of the large-scale jet is NWW. Images based on numerical simulations of BH accretion flows suggest that the projected BH spin axis should be oriented SSW. Alternatively, if the spin axis is matched with the jet direction, emission from the SEE sector of the photon ring cannot be accounted for. We explore highly simplified toy models for geometric distribution and kinematics of emitting regions in the Kerr metric, and perform ray tracing to calculate the corresponding images. We strictly assume that (1) the BH spin vector is fixed to the jet axis, (2) the emitting regions are symmetric with respect to the BH spin, (3) the emissivities are isotropic in the local rest frames. Emission from the crescent sector SSE — SWW can be readily explained in terms of an equatorial ring with outer radius $r_{\rm max} \simeq 6M$ and either circular or plunging geodesic flows, regardless of the value of BH spin. In the case of plane-symmetric polar caps with plunging geodesic flows, the dominant image of the cap located behind the BH is sensitive to the angular momentum of the emitter. Within the constraints of our model, we have not found a viable explanation for the observed brightness of the SEE sector. We suggest that the most likely solution to this problem is that emissivities are not locally isotropic. Polarimetric results from the EHT will be essential to verify the theoretically expected alignment of the BH spin with the large-scale jet.
K. Nalewajko, M. Sikora and A. Różańska
Thu, 29 Aug 19
4/55
Comments: 5 pages, 5 figures, submitted to A&A Letters
You must be logged in to post a comment.