First Light for GRAVITY!

January 13, 2016
A new astronomical high-tech instrument called GRAVITY has been successfully tested at Paranal Observatory of the European Southern Observatory (ESO) in Chile. It combines the light from several telescopes in order to visualize the finest details of celestial objects. Among the most important tasks of the instrument are observations of the immediate environment of the supermassive black hole at the center of our Milky Way, of exoplanet motions, or of structures within the disks of emerging new solar systems. The instrument working in infrared light was built with participation of the Max Planck Institute for Astronomy (MPIA) in Heidelberg.

One of the greatest challenges in observational astronomy is the detection of very faint details of the extremely distant objects in the universe. However, the maximum possible resolution of a telescope depends on the diameter of its optics, which is currently limited at about 10 meters even in case of the largest reflecting telescopes in the world. However, there is a trick to overcome this limit: by combining the light from several telescopes in a – by the way - extremely complicated procedure (the interferometry), one can achieve a resolution that is determined by the distances between the individual telescopes.

Thus - at the ESO-Observatory at Paranal in Chile - it is possible to simulate a virtual telescope of up to 200 meters in diameter by combining the four main 8m-telescopes and their four smaller 1.8m Auxiliary-Telescopes. With this technique the famous Very Large Telescope (VLT) turns into the VLT-Interferometer (VLTI).

In a first step, GRAVITY was now successfully tested by bundling the infrared light of the four Auxiliary Telescopes. The first operation including the other large telescopes is planned during the year.

But for a successful implementation of the final stage – that means with highest sensitivity and resolution – one has to overcome a very critical hurdle which normally restricts the possible power of a telescope dramatically: the blurring of starlight by the Earth´s atmosphere. The MPIA-part of the project is focused exactly on the solution of this fundamental problem.

"The main MPIA contributions to GRAVITY are four systems of the so-called Adaptive Optics. During the year 2016, the four 8m telescopes of the VLT will be equipped with wavefront-sensors that can analyze the infrared light of individual stars for correcting the atmospheric image smear" says Dr. Wolfgang Brandner from MPIA, co-I of the project."The much more focused light leads then to a significant increase in sensitivity of the instrument".

Thanks to the high resolution, a discovery was made with GRAVITY already during the test observations - namely that one of the most famous stars in the center of the Orion Nebula is actually a double star. For more information about this discovery and about the challenges of interferometry with GRAVITY, see the ESO press release at

The GRAVITY consortium is led by the Max Planck Institute for Extraterrestrial Physics, in Garching, Germany. The other partner institutes are:

LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, Meudon, Frankreich

Max-Planck-Institut für Astronomie (MPIA) in Heidelberg

Physikalisches Institut der Universität Köln

IPAG, Université Grenoble Alpes/CNRS, Frankreich

Centro Multidisciplinar de Astrofísica, CENTRA (SIM), Lissabon und Porto, Portugal

ESO Garching

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