Black Hole Probes Sees It’s First Light

“During its first light, and for the first time in the history of long baseline interferometry in optical astronomy, GRAVITY could make exposures of several minutes, more than a hundred times longer than previously possible,” commented Frank Eisenhauer. “GRAVITY will open optical interferometry to observations of much fainter objects, and push the sensitivity and accuracy of high angular resolution astronomy to new limits, far beyond what is currently possible.”

As part of the first observations the team looked closely at the bright, young stars known as the Trapezium Cluster , located in the heart of the Orion star-forming region. Already, from these first commissioning data, GRAVITY made a small discovery: one of the components of the cluster was found to be a double star [3].

The key to this success was to stabilise the virtual telescope for long enough, using the light of a reference star, so that a deep exposure on a second, much fainter object becomes feasible. Furthermore, the astronomers also succeeded in stabilising the light from four telescopes simultaneously — a feat not achieved before. The newly discovered double star is Theta1 Orionis F, and the observations were made using the nearby brighter star Theta1 Orionis C as the reference.

GRAVITY can measure the positions of astronomical objects on the finest scales and can also perform interferometric imaging and spectroscopy. GRAVITY aims to measure the positions of objects on scales of order ten microarcseconds, and perform imaging with four milliarcsecond resolution. 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 studying the environments around black holes.

 

In particular, GRAVITY will probe what happens 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 choice of the name of the instrument. This is a region where behaviour is dominated by Einstein’s theory 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 regions around the supermassive black holes at the centres of other galaxies. It will also excel at probing the motions 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.