Evidence of a Black Hole in the Center of the Milky Way:
The picture below is a view of the very center of the Milky Way obtained in mid 2002 from a combination of three infrared wavebands. The compact objects are stars, and two yellow arrows mark the location of Sagittarius A*, the black hole candidate within the radio source Sagittarius A. We can see objects within one light year of the galactic center! In this image one light year equals 8 arc seconds.
The next picture is another infrared image looking even more closely at the Milky Way's center. Black hole candidate Sagittarius A* is marked with a cross. The width of the picture is about 70 light days or about 0.2 light years.
The next amazing picture shows the observed orbit of a star called S2 around the black hole candidate Sagittarius A*. Star S2 is about 7 times the diameter of our Sun and has 15 times the mass of our Sun. The elliptical orbit (with an eccentricity of 0.87) of S2 has been observed since 1992, and about two thirds of its 15.2 year orbit has been traced out. The closest approach happened in early 2002 when S2 came within about 17 light hours of Sagittarius A*! 17 light hours is about 123 astronomical units, or about 1.5 solar system diameters! This is a close approach, but S2 was still about 64 times more distant from Sagittarius A* than the tidal disruption distance of 16 light minutes. From the observed orbit of S2 and other nearby masses the mass of Sagittarius A* can be calculated to be 2.6 million solar masses with an uncertainty of .2 million solar masses. The conclusion is that Sagittarius A* is a 2.6 million solar mass object smaller than 1.5 solar system diameters! Sure does look like a black hole!