GRAVITY observations further confirm the general theory of relativity.
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Sagittarius A * and its star cluster. Source: original article.

The European Southern Laboratory (European Southern Observatory, ESO) using the VLT system (Very Large Telescope, OBT) first discovered the effects predicted by Einstein’s General Theory of Relativity (GTR) when observing the motion of a star that went through a powerful gravitational field of a supermassive black hole Sagittarius A * in the center of the Milky Way.

Data were obtained as a result of GRAVITY consortium formed under the leadership of the Institute for Extraterrestrial Physics Max Planck (Max Planck Institute for Extraterrestrial Physics, MPE), Germany, in collaboration with the National Center for Scientific Research (Centre National de la Recherche Scientifique, CNRS), Paris Observatory (PSL), University of Grenoble-Alpes and several other French institutes. The consortium published an article summarizing 26 years of observations with ESO telescopes in Chile, published in Astronomy and Astrophysics on July 26, 2018.

Sagittarius A * (Sagittarius A *, Sgr A *) is located in the center of our galaxy, twenty-six thousand light years from Earth. This black hole, four million times heavier than the Sun, is surrounded by so-called "S-stars", which are accelerated in the field of its attraction to insane speeds.

The general theory of relativity describes the effect of large masses, and in particular, black holes, on the motion of stars; therefore, the Sagittarius A * cluster is an excellent testing ground for confirming the GTO hypotheses.

Astronomers used three VLT telescopes - NACO, SINFONI and the newly built GRAVITY - to track the fate of one particular star, S2, before and after it passed close to Sagittarius A * on May 18, 2018. At the same time, GRAVITY achieved a resolution of a picture of 50 angular microseconds - this is how to see a tennis ball on the Moon, looking at it from the Earth. Such accuracy allowed literally every hour to estimate the S2 offset relative to the black hole; the distance between the celestial bodies at the time of passage was 120 times greater than from the Earth to the Sun, while the star accelerated to 8000 km / s, 2.7% of the speed of light. This inevitably should have led to the apparent manifestation of the effects of GR.

Combining the results obtained by GRAVITY with the preceding observations of NACO and SINFONI, the scientists managed to findredshift that Einstein predicted.

The red shift represents the shift of the emission spectrum of an object to the red (long-wave) side under the influence of a powerful gravitational field, which is quite easily detected by the instruments; but the redshift in the field of the black hole had never before been observed.

The information obtained will serve as one more confirmation of the general theory of relativity and material for analyzing the effects caused by high gravity. The shift of the spectra of the star S2 will last for several more months, which may provide additional data on the mass distribution around Sagittarius A *.

"Observation of the red shift under the influence of gravity for the orbit of the star S2 near the supermassive black hole in the galactic center", GRAVITY Collaboration, July 26, 2018, Astronomy and Astrophysics.

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