Free Astronomy Magazine March-April 2016

SPACE CHRONICLES First light for future black hole probe by ESO T he GRAVITY instrument com- bines the light from multiple telescopes to form a virtual telescope up to 200 metres across, using a technique called interferome- try. This enables the astronomers to de- tect much finer de- tail in astronomical objects than is pos- sible with a single telescope. Since the summer of 2015, an inter- national team of astronomers and engineers led by Frank Eisenhauer (MPE, Garching, Germany) has been installing the in- strument in spe- cially adapted tun- nels under the Very Large Telescope at ESO’s Paranal Observatory in northern Chile. The VLTI tunnels and beam-combining room have recent- ly undergone significant construc- tion work to accommodate GRAVITY as well as to prepare for other fu- ture instruments. This is the first stage of commissioning GRAVITY within the Very Large Telescope In- terferometer (VLTI). A crucial mile- stone has now been reached: for the first time, the instrument success- fully combined starlight from the four VLT Auxiliary Telescopes. It would be more accurate to call this step “first fringes” as the mile- Z ooming in on black holes is the main mission for the newly installed instru- ment GRAVITY at ESO’s Very Large Telescope in Chile. During its first observa- tions, GRAVITY successfully com- bined starlight using all four Aux- iliary Telescopes. [ESO/GRAVITY consortium] omy, GRAVITY could make expo- sures of several minutes, more than a hundred times longer than pre- viously possible,” commented Frank Eisenhauer. “GRAVITY will open op- tical interferometry to observations of much fainter objects, and push the sensitivity and accuracy of high stone was the first successful com- bination of light from the different telescopes so that the beams inter- fered and fringes were formed and recorded. “During its first light, and for the first time in the history of long base- line interferometry in optical astron-