First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring

Abstract

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.

Universal polarimetric signatures of the black hole photon ring

“…1 We also assume that propagation effects are negligible, thereby ignoring effects from absorption, scattering, and dispersion. While we expect absorption and scattering to be weak for EHT observations of M87 * , whose emission region is thought to be optically thin with an electron density of only n e ∼ 10 4 cm −3 [10], Faraday effects from plasma birefringence are not expected to be negligible [12,13]. Nevertheless, the universal signature that we describe is comprised of multiple consistency relations and is achromatic, whereas Faraday effects are chromatic.…”

Shadow and quasinormal modes of a rotating loop quantum black hole

“…The calculations of the shadow size and shape, and their observational implications from different black hole spacetimes or spacetimes of compact objects with exotic matters ether in general relativity or in modified theories of gravity have been extensively studied, see, for example, . Recently, the first observational data of the shadow image captured by EHT [1][2][3][4][5][6] have been used for constraining the black hole parameters and deviations from the Kerr metric [49][50][51][52][53]. Although these constraints are still not stringent enough, these works do show that the observational data does have the capacity for constraining black hole parameters beyond those presented in GR.…”

Shadow of a spinning black hole in an expanding universe

“…In recent years, various kinds of astronomical observations strongly reveal that black holes do exist in our universe. The evidences so far are not limited to gravitational wave detection by LIGO and Virgo, but also include the images of black holes by Event Horzion Tecescope (EHT) [1][2][3][4][5][6]. However, compared to the precision of LIGO and Virgo, the pictures of black holes captured by EHT are not clear enough.…”