Free Astronomy Magazine March-April 2016

SPACE CHRONICLES T his picture shows some of the large and international GRAVITY team during initial observations at the Paranal Observatory. [ESO/ GRAVITY consortium] telescopes simultaneously — a feat not achieved before. GRAVITY can measure the positions of astronomical objects on the finest scales and can also perform interfer- ometric imaging and spectroscopy. GRAVITY aims to measure the posi- tions of objects on scales of order ten microarcseconds, and perform imaging with four milliarcsecond res- olution. If there were buildings on the moon, GRAVITY would be able to spot them. Such extremely high resolution imaging has many applications, but the main focus in the future will be study- ing the environments around black holes. In particular, GRAVITY will probe what hap- pens in the extremely strong gravitational field close to the event horizon of the supermassive black hole at the centre of the Milky Way — which explains the T his zoom video starts with a broad view of the fa- mous constellation of Orion (The Hunter) and then shows successively more detailed images of the region with different telescopes. The final view from GRAVITY reveals far finer detail around one of the fainter cluster stars than could be detected even with the NASA/ESA Hubble Space Telescope. [ESO/M. McCaughrean/GRAV- ITY consortium, Nick Risinger (skysurvey.org)] choice of the name of the instru- ment. This is a region where behav- iour is dominated by Einstein's the- ory of general relativity. In addition, it will uncover the details of mass accretion and jets — processes that occur both around newborn stars (young stellar objects) and in the re- gions around the supermassive black holes at the centres of other galaxies. It will also excel at probing the mo- tions of binary stars, exoplanets and young stellar discs, and in imaging the surfaces of stars. So far, GRAVITY has been tested with the four 1.8- metre Auxiliary Telescopes. The first observations using GRAVITY with the four 8-metre VLT Unit Telescopes are planned for later in 2016. n