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Register a new userA Jet-Bases Emission Model of the EHT 2017 Image of M87*
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We carry out general relativistic ray-tracing radiative-transfer calculations to study whether a localized emission from $e^{pm}$ plasma rings created at the stagnation surface in the jet funnel, to which we refer as stagnation rings, can explain the ring image of M87 observed by Event Horizon Telescope (EHT) 2017. The resultant images consist of the direct image of the stagnation rings and the ring images formed via the strong deflection by the black-hole (BH) gravity, to which we refer as quasi photon-ring. For the model with the BH spin $a_* = 0.99$, the direct image of the counter-jet and quasi photon-ring are almost coincident to the photon ring with diameter $sim 40 mu{rm as}$, while the approaching jet shows the small ring-image inside them. The synthetic observation image assuming the EHT 2017 array is consistent with that observed in M87, because the array is a bit sparse to detect the inner ring image. This indicates that the ring image in M87 might contain the important feature of the jet bases in addition to the photon ring. We find that forthcoming EHT observations can resolve the stagnation-ring image and may enable us to explore the plasma-injection mechanism into the jet funnel.
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Our understanding of strong gravity near supermassive compact objects has recently improved thanks to the measurements made by the Event Horizon Telescope (EHT). We use here the M87* shadow size to infer constraints on the physical charges of a large variety of nonrotating or rotating black holes. For example, we show that the quality of the measurements is already sufficient to rule out that M87* is a highly charged dilaton black hole. Similarly, when considering black holes with two physical and independent charges, we are able to exclude considerable regions of the space of parameters for the doubly-charged dilaton and the Sen black holes.
Slightly more than two years ago the Event Horizon Telescope (EHT) team presented the first image reconstruction around shadow for the supermassive black hole in centre of M87. It gives an opportunity to evaluate the shadow size. Recently, the EHT team constrained parameters (charges) of spherical symmetrical metrics of black holes from an estimated allowed interval for shadow radius from observations of M87*. In our papers we obtained analytical expressions for shadow radius as a function of charge (including a tidal one) in the case of the case of Reissner -- Nordstrom metric. Some time ago Bin-Nun proposed to apply Reissner -- Nordstrom metric with a tidal charge as an alternative to the Schwarzschild metric in Sgr A*. If we assume that Reissner -- Nordstrom black hole with a tidal charge exists in M87*, therefore, based on results of shadow evaluation for M87* done by the EHT team we constrain a tidal charge. Similarly, we evaluate a tidal charge from shadow size estimates for Sgr A*.
New high-resolution Very Long Baseline Interferometer observations of the prominent jet in the M87 radio galaxy show a persistent triple-ridge structure of the transverse 15-GHz profile with a previously unobserved ultra-narrow central ridge. This radio structure can reflect the intrinsic structure of the jet, so that the jet as a whole consists of two embedded coaxial jets. A relativistic magnetohydrodynamic model is considered in which an inner jet is placed inside a hollow outer jet and the electromagnetic fields, pressures and other physical quantities are found. The entire jet is connected to the central engine that plays the role of a unipolar inductor generating voltage between the jets and providing opposite electric currents, and the charge neutrality and current closure together with the electromagnetic fields between the jets can contribute to the jet stabilization. The constant voltage is responsible for the similar widening laws observed for the inner and outer jets. This jet-in-jet structure can indicate simultaneous operation of two different jet-launching mechanisms, one relating to the central supermassive black hole and the other to the surrounding accretion disc. An inferred magnetic field of 80 G at the base is sufficient to provide the observed jet luminosity.
The millimeter bump, as found in high-resolution multi-waveband observations of M87, most possibly comes from the synchrotron emission of thermal electrons in advection dominated accretion flow(ADAF). It is possible to constrain the accretion rate near the horizon if both the nuclear millimeter emission and its polarization are produced by the hot plasma in the accretion flow. The jet power of M87 has been extensively explored, which is around $8_{rm -3}^{+7}times10^{42} {rm erg/s}$ based on the analysis of the X-ray cavity. The black hole(BH) spin can be estimated if the jet power and the accretion rate near the horizon are known. We model the multi-wavelength spectral energy distribution (SED) of M87 with a coupled ADAF-jet model surrounding a Kerr BH, where the full set of relativistic hydrodynamical equations of the ADAF are solved. The hybrid jet formation model, as a variant of Blandford-Znajek model, is used to model the jet power. We find that the SMBH should be fast rotating with a dimensionless spin parameter $a_{*}simeq0.98_{rm -0.02}^{+0.012}$.
The Event Horizon Telescope (EHT) has recently delivered the first resolved images of M87*, the supermassive black hole in the center of the M87 galaxy. These images were produced using 230 GHz observations performed in 2017 April. Additional observations are required to investigate the persistence of the primary image feature - a ring with azimuthal brightness asymmetry - and to quantify the image variability on event horizon scales. To address this need, we analyze M87* data collected with prototype EHT arrays in 2009, 2011, 2012, and 2013. While these observations do not contain enough information to produce images, they are sufficient to constrain simple geometric models. We develop a modeling approach based on the framework utilized for the 2017 EHT data analysis and validate our procedures using synthetic data. Applying the same approach to the observational data sets, we find the M87* morphology in 2009-2017 to be consistent with a persistent asymmetric ring of ~40 uas diameter. The position angle of the peak intensity varies in time. In particular, we find a significant difference between the position angle measured in 2013 and 2017. These variations are in broad agreement with predictions of a subset of general relativistic magnetohydrodynamic simulations. We show that quantifying the variability across multiple observational epochs has the potential to constrain the physical properties of the source, such as the accretion state or the black hole spin.
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