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MrPlow writes:

Submitted via IRC for Bytram

A European team of astronomers have used the new GRAVITY instrument at ESO's Very Large Telescope to obtain exciting observations of the centre of the Milky Way by combining light from all four of the 8.2-metre Unit Telescopes for the first time. These results provide a taste of the groundbreaking science that GRAVITY will produce as it probes the extremely strong gravitational fields close to the central supermassive black hole and tests Einstein's general relativity.

In short, there's a 15 solar-mass star in an elliptical orbit around the 4-million-solar-mass black hole in Sagittarius A* that, in 2018, will approach to within 17 light-hours (3 times the distance from the Sun to Pluto) and will be traveling at 2.5% of the speed of light.

Source: https://www.eso.org/public/news/eso1622/

This is an amazing instrument; see the Animation of the path of a light ray through GRAVITY. For more information on the instrument, see GRAVITY — The second generation VLTI instrument for precision narrow-angle astrometry and interferometric imaging.

This is an ambitious project, its Science Objectives are:

GRAVITY will carry out the ultimate empirical test to show whether or not the Galactic Centre harbours a black hole (BH) of four million solar masses and will finally decide if the near-infrared flares from Sgr A* originate from individual hot spots close to the last stable orbit, from statistical fluctuations in the inner accretion zone or from a jet. If the current hot-spot interpretation of the near-infrared (NIR) flares is correct, GRAVITY has the potential to directly determine the spacetime metric around this BH. GRAVITY may even be able to test the theory of general relativity in the presently unexplored strong field limit. GRAVITY will also be able to unambiguously detect intermediate mass BHs, if they exist. It will dynamically measure the masses of supermassive BHs (SMBHs) in many active galactic nuclei, and probe the physics of their mass accretion, outflow and jets with unprecedented resolution. Furthermore, GRAVITY will explore young stellar objects, their circumstellar discs and jets, and measure the properties of binary stars and exoplanet systems. In short, GRAVITY will enable dynamical measurements in an unexplored regime.

[Update] Also covered at Ars Technica .

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