By Ron Cowen
By tracking a star near the center of our galaxy, astronomers have found the best evidence yet that a supermassive black hole lies at the Milky Way’s core. Although observations have long suggested that the galaxy harbors a monster black hole, they didn’t conclusively rule out less exotic concentrations of mass (SN: 9/8/01, p. 148: Galaxy’s Black Hole: X Rays Mark Spot).
The closest that the star observed by the astronomers ventures to the galaxy’s center is a distance three times that between Pluto and the sun. Traveling 5,000 kilometers per second, the star–known as S2–takes a mere 15 years to complete one orbit of the galaxy’s core. Researchers now have tracked S2 for 10 years.