{"id":12107,"date":"2022-03-18T11:06:57","date_gmt":"2022-03-18T10:06:57","guid":{"rendered":"https:\/\/www.einstein-online.info\/?post_type=spotlight&p=12107"},"modified":"2022-03-21T08:45:10","modified_gmt":"2022-03-21T07:45:10","slug":"vlti","status":"publish","type":"spotlight","link":"https:\/\/www.einstein-online.info\/en\/spotlight\/vlti\/","title":{"rendered":"Deep looks into the center of the Milky Way"},"content":{"rendered":"\n

There is a supermassive black hole<\/a> at the center of our Milky Way<\/a>. Its strong radio emissions<\/a> led to the name Sagittarius A*: It is the strongest (A) radio source in the constellation Sagittarius. The nature of this radio source has been confirmed by stellar motions that researchers have observed since the 1990s. From the stars\u2019<\/a> orbits, they determined the extent and mass of the central object. Given the result, the scientists concluded that the central object was a black hole. Andrea Ghez (University of California in Los Angeles, USA) and Reinhard Genzel (Max Planck Institute for Extraterrestrial Physics in Garching, Germany) received the Nobel Prize in Physics in 2020 for this finding, together with the theoretical physicist Roger Penrose<\/a>.<\/p>\n\n\n\n

High zoom in combination<\/h2>\n\n\n\n

The observations of the stellar motions at the center of our galaxy have been continued with increasing precision. With the Very Large Telescope Interferometer (VLTI), astronomers can now zoom in 20 times closer to the center of our galaxy than before.<\/p>\n\n\n\n

The VLTI consists of the four telescopes of the Very Large Telescope (VLT) of the European Southern Observatory in Chile \u2013 an instrument also used by Nobel Prize winner Genzel. Together with four other, smaller mirrors, the telescopes \u2013 each eight meters in diameter \u2013 collect the light that is superimposed for VLT interferometry. An instrument called GRAVITY<\/a>, which has been in operation since 2016, serves as the interferometer. It allows for a high spatial resolution, equivalent to that of a single telescope with a diameter of 120 meters. As a result, the technology has enabled several new discoveries.<\/p>\n\n\n\n

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The Paranal observatory with the four 8.2 meter telescopes of the Very Large Telescrope, the four auxillary mirrors and the VLT Survey Telescope. Credit: ESO\/G.H\u00fcdepohl<\/figcaption><\/figure><\/div>\n\n\n\n

Precise measurement of star orbits<\/h2>\n\n\n\n

In 2020, for example, researchers confirmed an effect of general relativity: They showed that the orbit of the star S2 does not follow an ellipse, as predicted by Newton’s theory of gravity. Rather, the orbit itself undergoes a rotation, giving it the shape of a rosette. In our solar system, the same effect is particularly strong in the orbit of Mercury. With their observations from the center of the Milky Way, the researchers demonstrated this so-called Schwarzschild precession at a black hole for the first time.<\/p>\n\n\n\n

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Artistic impression of S2’s orbit: It doesn’t have the shape of an ellipse, but of a rosette. Credit: ESO\/L. Cal\u00e7ada<\/figcaption><\/figure><\/div>\n\n\n\n

Between March and July 2021, astronomers took another look at the stars in the galactic center. Indeed, they moved exactly as predicted by general relativity<\/a> \u2013 for objects orbiting a black hole with a mass of 4.3 million solar masses. The researchers were thus able to specify the mass of the black hole to this value. And they determined its position more precisely: The center of our Milky Way is 27,000 light-years<\/a> away from us.<\/p>\n\n\n\n

A record and a new discovery<\/h2>\n\n\n\n

During the observations, the star S29 passed the black hole within record proximity: at a speed of 8740 kilometers per second, it moved past Sagittarius A* at a distance of 13 billion kilometers. That is almost three times the distance of our outermost planet Neptune from our Sun. As of 2022, researchers had never observed a star passing the black hole faster or at a smaller distance. Thus, the central object cannot be larger than the observed minimum distance from S29 to the center.<\/p>\n\n\n\n

A previously unobserved star also entered the astronomers’ field of view: S300, which had remained undetected until 2021 due to its faint light. This time, the astronomers were able to see it with the VLTI.<\/p>\n\n\n\n

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