Wednesday, March 27

This is Sagittarius A*, the black hole at the center of our galaxy


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Astronomers believe that virtually every galaxy has a supermassive black hole at its center, a region of space so dense that nothing falling into it, not even light, can escape. In the heart of ours, the Milky Way, there is also one. It is called Sagittarius A*, for its location in the constellation of Sagittarius. And, if everything goes according to the majority of scientific ‘pools’, in a few hours we will see his photograph for the first time thanks to the efforts of the Event Horizon Telescope or Event Horizon Telescope (EHT), an international team formed by two hundred astronomers who will reveal their “revolutionary results” on this “monster” that inhabits the center of our galaxy.

Located 26,000 light-years from the Sun, Sagittarius A* is extremely heavy: its mass is equivalent to that of four million suns. It was identified in the late 1990s by astronomers at the Max Planck Institute for Extraterrestrial Physics in Garching (Germany) and the University of California, due to the powerful attraction it exerts on nearby stars in the same region of space, pulling them at speeds giddy. The German Reinhard Genzel and the American andrea ghez They received the 2020 Nobel Prize in Physics for this discovery.

Until now, the behavior of the bodies around Sagittarius A* has been the only way to infer its presence. Both Genzel’s and Ghez’s groups accurately traced the orbit of one particular star, S2, which reached the closest distance to Sagittarius A* in May 2018 – less than 20 billion kilometers (120 times the distance between the Sun and Earth). The Genzel-led team found that the light emitted by the star near the supermassive black hole was stretched to longer wavelengths, an effect known as gravitational displacement, confirming for the first time Einstein’s general relativity near a supermassive black hole. In early 2020, the team announced that they had seen S2 dance around the supermassive black hole, showing that its orbit is in the shape of a rosette, an effect called Schwarzschild precession which was predicted by Einstein.

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The astronomers also measured the velocities of four distant stars around the black hole. The motion of the stars indicates that the mass at the center of the galaxy is composed almost entirely of Sagittarius A* matter, leaving little room for stars, other black holes, interstellar gas and dust, or dark matter.

circular structure

Normally, the black hole is quiet and produces billions of times less energy than giant black holes in other galaxies. Last February, a scientific team led by Ilje Cho, a researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC), published a paper in which he pointed out that the intrinsic structure of Sagittarius A* is almost circular. To reach this conclusion, the scientists used the VLBI technique, which consists of the synchronized use of numerous geographically separated radio telescopes, so as to create a virtual telescope the size of the distance between the telescopes.

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