This artist’s impression shows stars orbiting the supermassive black hole at the center of the Milky Way. It will make its closest approach in 2018, coming to within just 17 light hours. (credit: ESO)

After spending the better part of a decade closely observing the movement of the star S2, which has a mass about 15 times that of the Sun, a team of astrophysicists concluded in 2002 that it orbited the black hole at the center of the galaxy. This is because the orbital dynamics of S2 were extreme, with an orbital period of about 15.5 years and a maximum velocity of 2.5 percent the speed of light. These observations provided the final proof astronomers needed to confirm that the compact radio source Sagitarrius A* was, in fact, that black hole.

Since then astronomers have been keenly interested in the star S2 because its movement can tell them much about the supermassive black hole at the galaxy’s center. They can also test some ideas about general relativity when the star makes its closest approach to the black hole, within about 17 light hours, in 2018. And now, they have a powerful instrument to do just that.

The European Southern Observatory says its GRAVITY instrument has made its first observations, and they were successful. The instrument employs four 8.2-meter telescopes that are part of the “Very Large Telescope” facility in Chile. By using the telescope’s interferometer capabilities, astronomers will be able to obtain ultra-precise positions of the orbiting star.