[awsnmpou] Angular diameters of 2 supermassive black holes

Previously: Schwarzschild radius formula, noting that event horizon radius is proportional to mass.

Sagittarius A* at the center of the Milky Way: 4.31e6 solar mass.  If it is not rotating, then Schwarzschild radius = 1.3e10 m = 4.1e-7 parsec.  Distance 7860-8178 parsec.  (All figures from Wikipedia.)  Half angle via arcsine = 5.0e-11 to 5.2e-11 radian.  (Arcsine is more accurate than arctangent by 7e-32 radian, though such accuracy is irrelevant given the low precision inputs.)  Angular diameter = 2.1e-5 - 2.2e-5 arcsecond.

M87 central black hole (aka M87*): 6.5e9 solar mass, so nonrotating (which is false) radius 1.9e13 m = 6.2e-4 pc.  Distance 16.8e6 pc.  (Figures from "First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole".)  Half angle = 3.7e-11 radian.  Angular diameter = 1.5e-5 arcsecond. 

It's surprising regarding M87 that, despite being 2100 times farther away than the center of the Milky Way, its black hole's angular size is of the same order of magnitude, thanks to M87*'s mass 1500 times greater than Sgr A*.  If I were picking black holes to image, I initially would not have even considered an extragalactic black hole as a first target.  Who first suggested M87?  Are there other black holes with even larger angular size?  Something 100 times more massive and another 100 times further away seems imaginable, though we start to get into the early universe when there might not yet have been enough time for super super massive black holes to form.

The angular diameter of M87* is equivalent to earth viewed from a distance of 18 light years, or the sun viewed from a distance of 1970 light years.  M87* is 55 million light years away.  There might be some stars visible to the naked eye that have smaller angular diameters than M87* (not that you could resolve the disc of any of them with the naked eye).

Incidentally, M87*'s average density is 6.5e9 sunmass / (4/3*pi*(6.5e9*2 gauss_k^2 au^3 day^-2 c^-2)^3) = 0.44 kg / m^3 or 2300 times LESS dense than water.

Sgr A*: 9.92e5 kg/m^3 or 992 times MORE dense than water.