Free Astronomy Magazine September-October 2018

34 SEPTEMBER-OCTOBER 2018 SPACE CHRONICLES T his simulation shows the or- bits of stars very close to the super- massive black hole at the heart of the Milky Way. One of these stars, named S2, orbits every 16 years and is passing very close to the black hole in May 2018. This is a perfect laboratory to test gravitational physics and specif- ically Einstein's general theory of relativity. [ESO/L. Calçada/ spaceengine.org ] T his diagram shows the motion of the star S2 as it passes close to the super- massive black hole at the centre of the Milky Way. It was compiled from observations with the GRAVITY instrument in the VLT interferometer. At this point the star was travelling at nearly 3% of the speed of light and its shift in position can be seen from night to night. The sizes of the star and the black hole are not to scale. [ESO/MPE/GRAVITY Collaboration] Françoise Delplancke, head of the System Engineering Department at ESO, explains the significance of the observations: “Here in the Solar System we can only test the laws of physics now and under certain cir- cumstances. So it’s very important in astronomy to also check that those laws are still valid where the gravitational fields are very much stronger.” Continuing observations are ex- pected to reveal another relativistic effect very soon — a small rotation of the star’s orbit, known as Schwarz- schild precession — as S2 moves away from the black hole. Xavier Barcons, ESO’s Director Gen- eral, concludes: “ESO has worked with Reinhard Genzel and his team and collaborators in the ESO Mem- ber States for over a quarter of a century. It was a huge challenge to develop the uniquely powerful instruments needed to make these very delicate measurements and to deploy them at the VLT in Paranal. The discovery is the very exciting result of a re- markable partnership.” laboratory than he could have possi- bly imagined! Einstein has been proved right once more — in a much more extreme !