The M87 image made some astronomers famous recently as the first image of a black hole.

In the Milky Way, it has been concluded that there must be a black hole due to the movement of stars near the center. But why is there no such light effect in our black hole, as there is in M87? Or is it there, but we cannot see it for some reason?

Event Horizon Telescope image of the accretion disk around the black hole in M87


M87 is an active galaxy with an accreting, rotating central black hole of mass $M\simeq6.5\times10^9M_{\odot}$ (Akiyama et al. 2019). It is the inner disk surrounding this black hole that produces, among radiation, the 1.3 mm synchrotron emission observed by the Event Horizon Telescope, as well as the relativistic jets emitted perpendicular to the disk's plane.

The Milky Way is not currently an active galaxy, and while there is some evidence for a cool accretion disk around Sgr A* (Murchikova et al. 2019), it is sparse. The strongest constraints on Sgr A*'s accretion rate are about five orders of magnitude lower than M87*'s $\sim0.1M_{\odot}\;\text{yr}^{-1}$ (Di Matteo et al. 2003). The very low accretion rate onto Sgr A*, a black hole three orders of magnitude less massive, combine to indicate that any emission of the same sort from the Galactic center should be much less intense than that seen by the EHT from M87*.

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    $\begingroup$ There is also the issue that the variability timescale is much shorter for the Milky Way BH making it (I understand) much harder to get a good interferometric image, even though it should be on the same sort of angular scale. $\endgroup$ – Rob Jeffries Oct 13 at 11:36

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