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The parameter Schwarzschild Radius of Saggriatus A* is given in Wiki by 2.08×1015 (~0.2 ly)

see in Parameters http://en.wikipedia.org/wiki/Schwarzschild_radius

However, when I do the calculation with 4.3Mio Ms I get a different result: 12.7x10^9

https://www.google.de/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#safe=off&q=26.67384(10%5E(-11))4.3(10%5E6)1.989(10%5E(30))%2F(3*10%5E8)%5E2

Where is my error?

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The table you are referring to shows the Schwarzschild radius for the whole Milky Way galaxy, not it's SMBH, Sagittarius A$^*$.

The total mass content of the galaxy is about $10^{12}\,M_\odot\sim10^{42}\,\rm kg$, leading to $$ r=\frac{2GM}{c^2}\approx\frac{10^{-11}\times10^{42}}{\left(10^8\right)^2}=10^{15}\,\rm m $$

For Sag A$^*$, we can estimate it to be what you obtain: $$ r=\frac{2GM}{c^2}\approx\frac{10^{-11}\times10^{36}}{\left(10^8\right)^2}=10^{9}\,\rm m $$

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