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Evidence of a Supermassive Black Hole at the center of the Milky Way Galaxy

At the center of our Milky Way Galaxy lies a black hole with about 3 million times the mass of the Sun. Once a controversial claim, this astounding conclusion is now virtually inescapable and based on observations of stars orbiting very near the galactic center. Using one of the Paranal Observatory's very large telescopes and the sophisticated infrared camera NACO, astronomers patiently followed the orbit of a particular star, designated S2, as it came within about 17 light-hours of the center of the Milky Way (17 light-hours is only about 3 times the radius of Pluto's orbit). Their results convincingly show that S2 is moving under the influence of the enormous gravity of an unseen object which must be extremely compact -- a supermassive black hole. This deep NACO near-infrared image shows the crowded inner 2 light-years of the Milky Way with the exact position of the galactic center indicated by arrows. This is the position of the compact radio and X-ray source SgrA* ("Sagittarius A"), which is the black hole candidate.

NACO's ability to track stars so close to the galactic center can accurately measure the black hole's mass and perhaps even provide an unprecedented test of Einstein's theory of gravity as astronomers watch a star orbit a supermassive black hole.

This picture was obtained in mid-2002 with the NACO instrument at the 8.2-m VLT YEPUN telescope. It combines frames in three infrared wavebands between 1.6 and 3.5 Ám. The compact objects are stars and their colors indicate their temperature (blue = "hot", red = "cool"). There is also diffuse infrared emission from interstellar dust between the stars.

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