Abstract
ABSTRACT Black hole (BH) accretion is one of nature’s most efficient energy extraction processes. When gas falls in, a significant fraction of its gravitational binding energy is either converted into radiation or flows outwards in the form of BH-driven jets and disc-driven winds. Recently, the Event Horizon Telescope (EHT), an Earth-sized submillimetre radio interferometer, captured the first images of M87’s BH. These images were analysed and interpreted using general relativistic magnetohydrodynamics (GRMHD) models of accretion discs with rotation axes aligned with the BH spin axis. However, since infalling gas is often insensitive to the BH spin direction, misalignment between accretion disc and BH spin may be a common occurrence in nature. In this work, we use the general relativistic radiative transfer code bhoss to calculate the first synthetic radio images of (highly) tilted disc/jet models generated by our GPU-accelerated GRMHD code h-amr . While the tilt does not have a noticeable effect on the system dynamics beyond a few tens of gravitational radii from the BH, the warping of the disc and jet can imprint observable signatures in EHT images on smaller scales. Comparing the images from our GRMHD models to the 43 and 230 GHz EHT images of M87, we find that M87 may feature a tilted disc/jet system. Further, tilted discs and jets display significant time variability in the 230 GHz flux that can be further tested by longer-duration EHT observations of M87.
Highlights
There is observational evidence for misalignment between the accretion disk and black hole (BH) spin axis in both active galactic nuclei (AGN), BH X-ray binaries (XRBs) (e.g., Hjellming & Rupen 1995; Greene et al 2001; Maccarone 2002; Caproni et al 2006; van den Eijnden et al 2017; Russell et al 2019) and tidal disruption events (e.g., Pasham et al 2019), with theoretical studies of the growth of supermassive black holes (SMBHs) favouring randomly oriented accretion and affecting BH spin evolution (e.g., Volonteri et al 2005; King & Pringle 2006)
Each BH system is shown in the plane of the BH spin and the jet angular momentum vector, or, in other words, the φ = 0◦ plane rotated by the corresponding jet precession angle Pj
If we rotate our tilt angles of 0◦ (T0) 230 GHz image so that we match the orientation of the 43 GHz M87 jet to the 43 GHz general-relativistic radiative transfer (GRRT) image, we find that the southern crescent is shifted to the bottom right quarter of the image, and does not match well with the Event Horizon Telescope (EHT) observed M87 image
Summary
There is observational evidence for misalignment between the accretion disk and black hole (BH) spin axis in both active galactic nuclei (AGN), BH X-ray binaries (XRBs) (e.g., Hjellming & Rupen 1995; Greene et al 2001; Maccarone 2002; Caproni et al 2006; van den Eijnden et al 2017; Russell et al 2019) and tidal disruption events (e.g., Pasham et al 2019), with theoretical studies of the growth of supermassive black holes (SMBHs) favouring randomly oriented accretion and affecting BH spin evolution (e.g., Volonteri et al 2005; King & Pringle 2006). Periodic variations in the jet position with respect to the line of sight have been invoked. Model a Resolution rin rmax rout (Nr × Nθ × Nφ) [rg] [rg] All Model T0 Tinit [deg]. Tj∗, P∗j tsim [deg, deg] [105tg] T30 (18, 26, 78)
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