For the first time, observations with ESO’s Very Large Telescope (VLT) have shown that a star orbiting the supermassive black hole in the center of the Milky Way moves exactly as Einstein’s general theory of relativity predicts. Its orbit is shaped like a rosette and not like an ellipse, as Newton’s theory of gravity predicts. This long-awaited result was made possible by increasingly precise measurements over almost 30 years, which enabled scientists to uncover the secrets of the giant that lurks in the heart of our galaxy.
“Einstein’s general theory of relativity predicts that bound orbits of one object around another are not closed as in Newtonian gravity, but go forward in the plane of motion. This famous effect – first seen on the orbit of the planet Mercury around the sun – was that First Evidence for General Theory of Relativity One hundred years later we found the same effect in the motion of a star orbiting the compact radio source Sagittarius A * in the center of the Milky Way, this breakthrough in observation reinforces the evidence that Sagittarius A. * must be a supermassive one Being a black hole that is 4 million times the mass of the sun, “says Reinhard Genzel, director at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching and architect of the 30-year program led to this result.
Sagittarius A * is 26,000 light years from the sun and, with its dense cluster of stars, offers a unique laboratory for testing physics in an otherwise unexplored and extreme gravity regime. One of these stars, S2, is moving less than 20 billion kilometers (one hundred and twenty times as far as between the Sun and Earth) towards the supermassive black hole, making it one of the closest stars ever found in orbit, the massive one Giant. The next time it approaches the black hole, S2 races through space at almost three percent the speed of light and completes an orbit every 16 years. “After following the star in orbit for over two and a half decades, our exquisite measurements robustly capture the Schwarzschild precession of S2 on its way to contactor A *,” said Stefan Gillessen of MPE, who directed the analysis of the measurements released today in the diary Astronomy & astrophysics.
Most stars and planets have a non-circular orbit and therefore move closer and further away from the object around which they are rotating. The S2’s orbit moves, which means that its closest point to the supermassive black hole changes with each revolution, so that the next orbit is rotated relative to the previous one, creating a rosette shape. General relativity provides an accurate prediction of how much its orbit is changing, and the latest measurements from this research are in exact agreement with the theory. This effect, known as Schwarzschild precession, had never before been measured for a star around a supermassive black hole.
The study with ESO’s VLT also helps scientists learn more about the surroundings of the supermassive black hole at the center of our galaxy. “Since the S2 measurements follow the general relativity so well, we can set strict limits on how much invisible material there is, such as distributed dark matter or possible smaller black holes around contactor A *. This is of great interest for understanding the formation and Development of supermassive black holes, “said Guy Perrin and Karine Perraut, the project’s leading French scientists.
This result is the culmination of 27 years of observations of the S2 star with an instrument fleet at ESO’s VLT in the Atacama Desert in Chile. The number of data points that mark the position and speed of the star confirms the thoroughness and accuracy of the new research: The team carried out a total of more than 330 measurements using the GRAVITY, SINFONI and NACO instruments. With S2 taking years to orbit the super-massive black hole, it was critical to follow the star for nearly three decades to uncover the intricacies of its orbital motion.
The research was carried out by an international team led by Frank Eisenhauer from the MPE with employees from France, Portugal, Germany and ESO. The team consists of the GRAVITY collaboration, named after the instrument they developed for the VLT interferometer. It combines the light from all four 8-meter VLT telescopes to form a super telescope (with a resolution that corresponds to that of a telescope with a diameter of 130 meters). The same team reported another effect predicted by General Theory of Relativity in 2018: they saw that the light received by S2 was stretched to longer wavelengths when the star passed near Sagittarius A *. “Our results to date have shown that the light emitted by the star experiences general relativity. Now we have shown that the star itself perceives the effects of general relativity,” said Paulo Garcia, researcher at the Portuguese Center for Astrophysics and Gravitation and one of the leading scientists of the GRAVITY project.
With the upcoming ESO Extreme Large Telescope, the team believes it could see much fainter stars that circle even closer to the supermassive black hole. “If we’re lucky, we can catch stars so close that they actually feel the rotation, the spin of the black hole,” says Andreas Eckart from the University of Cologne, another of the project’s leading scientists. This would mean that astronomers would be able to measure the two quantities spin and mass that characterize Sagittarius A * and define space and time around it. “That would be a completely different level of relativity testing,” says Eckart.
This research was presented in the thesis “Detection of the Schwarzschild precession in the orbit of the star S2 near the massive black hole of the galactic center” Astronomy & astrophysics.
Supermassive black hole in the center of our galaxy may have a friend
Detection of the Schwarzschild precession in the orbit of the star S2 near the massive black hole of the galactic center, Astronomy & astrophysics (2020). DOI: 10.1051 / 0004-6361 / 202037813, https://www.aanda.org/articles… 3-20 / aa37813-20.html
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