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M87 and its black-hole (also see "Space Fact"). An image of this black-hole is presented to the world by the Event Horizon Telescope(s) (EHT) in April, 2019. However, close examination reveals that the image is a shadow (actually a silhouette) formed by dark object against radio frequency background, and the whole picture is in false colors. It is stitched together with missing data filled in by some sort of educated guessing, a.k.a. "Bayesian Inference". |
Figure 05-02r1 M87, Black-Hole [view large image] |
Figure 05-02r2 M87 BH Parms |
The following shows the theoretical base and processing involved in the imaging. |
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Figure 05-02s1 Interference |
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Figure 05-02s2 Interferometry |
Figure 05-02s3 VLBI |
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Figure 05-02t Black-hole Imaging |
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Earth) case, D = [(1 + v/c)/(1 - v/c)]1/2 which implies enhanced luminosity. For edge-on receding source v is replaced by -v so that D = [(1 - v/c)/(1 + v/c)]1/2 which implies reduced luminosity. However, even the approaching jet is absent in the M87 black-hole image because it is highly sensitive to observing wavelength as shown in the simulation images of Figure 05-02u and the accompanied video. The brightness of the jet becomes un-noticeable at the observational wavelength of 0.1 cm (see Figure 05-02u). |
Figure 05-02u Black-hole Jet |
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moves around because the environment around the black hole changes on a scale of several weeks. Strong magnetic fields stir the accretion disk and produce hotter spots that then orbit the black hole. See "The first-ever image of a black hole is now a movie". |
Figure 05-02w M87 Black Hole, |
In 2018, a separate team reported evidence of a blob of hot gas circling SgrA*, the Milky Way’s central black hole, over the course of around 1 hour. Because M87* is more than 1,000 times the size of SgrA*, the dynamics around M87* take longer to unfold. |
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It indicates that the emission occurs inside a magnetized plasma with lot of scrambling (reducing the degree of polarization). The pictures also show that the pattern varies in one day. Therefore, the maximum size of the emitting region would be no more than : ![]() which is a little bit larger than the Schwarzschild radius of the M87 black hole Rs ~ 2x1015 cm ~ 100 AU. |
Figure 05-02x M87 Magnetic Field [view large image] |
1 AU = 1.5x1013 cm (distance from Sun to Earth) |
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Figure 05-02y M87 Polarization [image, video] |
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be a black hole (see Figure 05-02z1). However, there is no jet in the 300 GHz radio image of the M87 black hole taken by EHT in 2019 and its supposedly refined image in 2021. The disappearance can be explained by weak synchrotron (non-thermal) emission at the higher frequency of 300 GHz (see Figure 05-02z2). The jet re-appears in the 2023 radio image at 100 GHz from the Global Millimetre VLBI Array (GMVA). It shows the twisted helix close to the black hole from the accretion disk. Thus, it requires lower frequency to see the non-thermal jet; while higher frequency shows the jet by thermal radiation. |
Figure 05-02z1 M87 Jet |
Figure 05-02z2 Radiation Types [view large image] |
There is no jet ~ 300 GHz because both types of emission are weak near that point. (see video in Figure 05-02u, and the "Formation of Jet"). |