A successful observation of the Milky Way center with the GRAVITY instrument

Artistic representation of stars orbting the supermassice black hole at the center of the Milky Way (Image ESO/L. Calçada)
Artistic representation of stars orbting the supermassice black hole at the center of the Milky Way (Image ESO/L. Calçada)

ESO has announced the successful first observation made using the new GRAVITY instrument on the VLT (Very Large Telescope). It’s operational on all four VLT UT 8.2-meter telescopes and the observation tests of a region near the center of the Milky Way  show that it’s working extremely well to provide high quality observations.

GRAVITY is part of the VLT interferometer, which means that it combines the light of more telescopes allowing to observe the details of an object as if it were using a telescope with a diameter equal to the separation between the physical ones. In this case, combining the light of the four Unit Telescopes (UT) they can get the resolution of a telescope with a diameter of 130 meters. They can also combinee the light of the four Auxiliary Telescopes (AT). The resolution and the accuracy are 15 times higher than those obtained with a single physical telescope.

The to study of the area close to the supermassive black hole at the center of the Milky Way is one of the main objectives of GRAVITY use. In particular, astronomers intend to make more precise measurements than the ones available of the gravitational field around this monster, also known as Sagittarius A* or simply Sgr A*, with a mass estimated at around 4 million solar masses. This will also allow to check that the effects of that field match those expected by Albert Einstein’s theory of general relativity.

To obtain these results, astronomers will use GRAVITY to observe a star named S2 orbiting the supermassive black hole with a period of 16 years. This star is dim so its early detection was an excellent result of the first observations. The new instrument will measure its position very precisely to determine its motion around the black hole.

This new instrument is available just in time to prepare the observations of the star S2 at its maximum proximity to the supermassive black hole. The event is happening in 2018, when S2 will be at about 17 light-hours from the black hole. At that moment it will have an estimated speed of around 30 million kilometers per hour, about 2.5% of light speed. In those conditions it will be possible to observe relativistic effects, which will be analyzed in great detail thanks to GRAVITY.

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