This long-sought result was made possible by increasingly accurate measurements over nearly thirty years, which allowed scientists to unravel the mysteries of the monster that lurks at the heart of our galaxy.
Observations made using The Very Large Telescope (VLT) of the Southern European Observatory (ESO) discovered for the first time that a star orbiting the supermassive black hole at the center of the Milky Way moves exactly as Einstein predicted in his general theory of relativity. Its orbit is in the shape of a rosette and not in the shape of an ellipse as Newton predicted in his theory of gravity. This long-sought result was made possible by increasingly accurate measurements over nearly thirty years, which allowed scientists to unravel the mysteries of the monster that lurks at the heart of our galaxy.
"Einstein's theory of general relativity predicts that bound orbits of one object around another are not closed, as in Newtonian gravity, but rather point (change direction) forward in the plane of motion. This famous effect—first seen in the orbit of Mercury around the Sun—was the first proof in favor of general relativity. A hundred years later we discovered the same effect in the motion of a star orbiting the source of concentrated radio transmission Sagittarius A* The region where the black hole is located at the center of the Milky Way This observational breakthrough strengthens the evidence that Sagittarius A* must be a supermassive black hole With a mass that is 4 million times greater than the mass of the sun, says Reinhard Gentzel, director of the Max Planck Institute for Foreign Physics (MPE in Gerching, Germany and the designer of the thirty-year plan that led to this result
Sagittarius A*, located 26,000 light-years from the Sun, and its dense cluster of stars provide a unique laboratory for experiments in extreme and otherwise unexplored gravitational regime physics. 2 of the distance between the Sun and the Earth and this makes it one of the closest stars ever found in orbit around the supermassive black hole at its closest approach to the black hole. For two and a half decades, our excellent measurements have firmly detected the Schwarzschild 20S in its orbit around Sagittarius A*," says Stephan Gilsen of MPE, who led the analysis of the measurements published today in the journal Astronomy & Astrophysics.
Most of the stars and planets have a non-circular orbit, so they move closer and further away from the body around which they revolve. 2S's orbit is skewed, meaning the location of its closest point to the supermassive black hole changes with each rotation, so the next orbit is rotated relative to the previous one, creating a rosette shape. General relativity provides an accurate prediction of how much the orbit will change and the latest measurements from this study match the theory exactly. This effect, called the Schwarzschild effect, has never before been measured for a star around a supermassive black hole of the type found at the center of every galaxy.
The research using ESO's VLT is also helping scientists learn more about the environment of the supermassive black hole at the center of the Milky Way. "Because the 2S measurements fit so well with general relativity we can put tighter limits on the amount of invisible matter such as diffuse dark matter or perhaps smaller black holes found around Sagittarius A*. This is of great interest for understanding the formation and evolution of black holes on -Massive say Guy Perrin and Karin Perot the leading scientists of the project in France.
This result is the culmination of 27 years of observing the 2S star using, most of the time, a fleet of instruments on ESO's VLT located in the Atacama Desert in Chile. The amount of data indicating the star's location and speed indicates the thoroughness and precision of the new study: the team made a total of more than 330 measurements, using the GRAVITY, SINFONI and NACO instruments. Because it takes 2S years to orbit the supermassive black hole, it was essential to follow the star for nearly three decades to reveal the intricacies of its orbital motion.
The research was carried out by an international team led by Frank Eisenhower from MPE with collaborators from France, Portugal, Germany and ESO. The team created the collaboration GRAVITY, named after the device they developed for the VLT inferometer, which combines the light of all four VLT 8 meter telescopes into a super telescope (with a resolution equivalent to that of a 130 meter diameter telescope). The same team reported in 2018 another effect predicted by general relativity: they saw that the light received from 2S was stretched to longer wavelengths as the star moved closer to Sagittarius A*. "Our previous result showed that the light emitted from the star experiences general relativity. Now we have shown that the star itself feels the effects of general relativity", says Paulo Garcia, a researcher at the Center for Astrophysics and Gravitation of Portugal and one of the lead scientists of the GRAVITY project.
Using the Extremely Large Telescope, ESO's next telescope, the team believes they will be able to see much fainter stars with an even closer orbit to the supermassive black hole. "If we're lucky, we might capture stars that are close enough to actually feel the black hole's swirling rotation," says Andreas Eckert from the University of Cologne, another lead scientist of the project. This means that astronomers will be able to measure both the swirling and mass quantities that characterize Sagittarius A* and define space and time around it. This will again be a completely different level of experimenting in relationships," says Eckert.
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