<P> An empirical correlation between the size of supermassive black holes and the stellar velocity dispersion σ (\ displaystyle \ sigma) of a galaxy bulge is called the M - sigma relation . </P> <P> Astronomers are very confident that the Milky Way galaxy has a supermassive black hole at its center, 26,000 light - years from the Solar System, in a region called Sagittarius A * because: </P> <Ul> <Li> The star S2 follows an elliptical orbit with a period of 15.2 years and a pericenter (closest distance) of 17 light - hours (7013180000000000000 ♠ 1.8 × 10 m or 120 AU) from the center of the central object . </Li> <Li> From the motion of star S2, the object's mass can be estimated as 4.1 million M, or about 7036820000000000000 ♠ 8.2 × 10 kg . </Li> <Li> The radius of the central object must be less than 17 light - hours, because otherwise, S2 would collide with it . In fact, recent observations of the star S14 indicate that the radius is no more than 6.25 light - hours, about the diameter of Uranus' orbit . </Li> <Li> No known astronomical object other than a black hole can contain 4.1 million M in this volume of space . </Li> </Ul> <Li> The star S2 follows an elliptical orbit with a period of 15.2 years and a pericenter (closest distance) of 17 light - hours (7013180000000000000 ♠ 1.8 × 10 m or 120 AU) from the center of the central object . </Li>

How many solar masses is the black hole at the center of the milky way