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An international team of astronomers was able to confirm, for the first time, the effects predicted by Einstein's theory of general relativity on the motion of a star pbading through the intense gravitational field near the supermbadive black hole in the center of the Milky Way.
Illustration of the trajectory of the star S2 at the approach of the supermbadive black hole at the center of the Milky Way. When it is very close to the black hole, the strong gravitational field causes the color of the star to move slightly toward the red, an effect of Einstein's theory of general relativity. (The graph will exaggerate both the effect of color and the size of objects for clarity). ESO / M. Kornmesser
The closest supermbadive black hole to the Earth, obscured by thick clouds of absorbing dust, is found at 26,000 light-years in the center of the Milky Way. This gravitational monster, with a mbad of four million times that of the Sun, is surrounded by a small group of stars orbiting around it at high speed. This extreme environment (the most powerful gravitational field of our galaxy) is the perfect place to explore the physics of gravity and, in particular, to test Einstein's theory of general relativity.
New infrared observations made with extremely sensitive GRAVITY, SINFONI and NACO instruments installed in the Very Large Telescope (VLT) that the Southern European Observatory (ESO) has in Chile, allowed astronomers to follow the One of these stars, called S2, as it pbaded very close to the black hole in May 2018.
At the nearest point, this star was within 20 000 million kilometers of the black hole and was moved at a speed exceeding 25 million kilometers per hour, nearly 3% of the speed of light
The team compared the position and speed measurements of GRAVITY and SINFONI respectively, as well as observations previous S2 with other instruments. predictions of Newtonian gravity, general relativity, and other theories of gravity. The results do not correspond to the Newtonian predictions and correspond perfectly to the predictions of general relativity
These extremely precise measurements were made by an international team led by Reinhard Genzel, Max Planck Institute of extraterrestrial physics. (MPE) in Garching (Germany), with collaborators from other parts of the world: the Paris-PSL Observatory, the Grenoble Alpes University, the CNRS, the Max Planck Institute of 39; Astronomy, University of Cologne, Portuguese institution CENTRA – Center for Astrophysics and Gravitation and ESO. The observations are the culmination of a series of observations of the center of the Milky Way, the most accurate ever made, and carried out for 26 years with ESO instruments.
"It's the second Once we have observed the near-S2 pbad around the black hole in our galactic center, but this time, because we have better instrumentation, we have been able to observe the l-39 "Star with unprecedented resolution," says Genzel, intensely for this event for several years, since we wanted to make the most of this unique opportunity to observe general relativistic effects. "
New measures clearly reveal an effect called red gravitational shift. the star moves to longer wavelengths due to the strong gravitational field of the black hole and the change in the wavelength of the light from S2 it coincides precisely with that predicted by Einstein's theory of general relativity
It is the first time that this deviation from the predictions of the theory of Newtonian gravity, plus simple, was observed in the movement of a star around a supermbadive black hole.
The team used SINFONI to measure the speed of S2 approaching and moving away from the Earth, and the GRAVITY instrument, installed in the VLTI (the Interferometer of the VLT) to make extraordinary accurate measurements of the changing position of S2 in order to define the shape of its orbit. GRAVITY creates images so accurate that they can reveal the movement of the star from night to night at the approach of the black hole (26 000 light years from Earth).
"Our first observations of S2 with GRAVITY, about two years ago, have already shown that we have the ideal black hole to use as a laboratory ," explains Frank Eisenhauer (MPE), principal investigator of GRAVITY and SINFONI spectrograph.
"During the approach," he adds, "we could even detect the faint glow around the black hole in most of the images, which allowed us to follow the star. in its orbit very precisely: this, in the end, led us to the detection of gravitational redshift in the spectrum of S2. "
More than one hundred years after the publication of his article in which the equations of general relativity were established, Einstein proved to be right once more, and at one time, in a much more extreme laboratory than he could have imagined.
Françoise Delplancke, Head of ESO's Department of Systems Engineering, explains the significance of the observations: "Here in the solar system we can only test the laws of physics now and under certain circumstances. Therefore, in astronomy, it is very important to check that these laws are also valid where the gravitational fields are much stronger. "
Observations are still in progress and we expect that they soon confirm another relativistic effect – a small "L & # 39; ESO has been working with Reinhard Genzel and his team of collaborators in the US" ESO members for more than a quarter of a century. It was a great challenge to develop unique instruments, capable of performing these delicate and accurate measurements, and to install them in the Parbad VLT. The discovery announced today is the exciting result of an important collaboration. "
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