Star’s Orbit Around Supermassive Black Hole Proves Einstein’s Theory Right

Data collected by ESO‘s Very Large Telescope (VLT) has unveiled for the first time ever that a star rotating around the supermassive black hole at the core of our Milky Way moves exactly in the way Einstein‘s general relativity theory suspected.

Its orbit has the shape of a rosette and not of an ellipse, as suggested by Newton‘s theory of gravity. The result was achievable by enhancing accurate measurements over about 30 years, which have allowed researchers to uncover the enigmas of the giant hiding at the center of our galaxy.

“Einstein’s General Relativity predicts that bound orbits of one object around another are not closed, as in Newtonian Gravity, but precess forwards in the plane of motion. This famous effect — first seen in the orbit of the planet Mercury around the Sun — was the first evidence in favor of General Relativity. One hundred years later we have now detected the same effect in the motion of a star orbiting the compact radio source Sagittarius A* at the center of the Milky Way. This observational breakthrough strengthens the evidence that Sagittarius A* must be a supermassive black hole of 4 million times the mass of the Sun,” explained Reinhard Genzel, Director at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany and the designer of the 30-year-long program that managed to get this result.

S2’s Orbit Identified

Sagittarius A* and the thick group of stars in its vicinity are located about 26,000 light-years from the Sun and makes an amazing testing ground for analyzing physics in an uncharted and intense system of gravity.

One of the stars, S2, raids in towards the supermassive black hole to close proximity of fewer than 200 billion kilometers, making it one of the nearest stars ever discovered in orbit around the black hole.

After monitoring the star in its orbit for more than two decades, the researchers’ measurements identified S2’s Schwarzschild precession in its trajectory around Sagittarius A*, Stefan Gillessen of the MPE, who led the analysis explained in an article published in the journal Astronomy & Astrophysics.

The majority of stars and planets don’t have a circular orbit and hence, move closer and further away from the cosmic body they are orbiting. S2’s orbit processes, which means that the location of its closest spot to the giant black hole changes with every turn, in such a way that the following orbit is rotated in relation to the previous one, generating a rosette shape.

It’s a First

General Relativity offers an accurate prediction of how much its orbit adjusts, and the most recent measurements from this study match the hypothesis exactly. This outcome, called Schwarzschild precession, has never before been calculated for a star orbiting a supermassive black hole. The research with ESO’s VLT also helps astronomers understand more about the surrounding environment of the giant black hole.

“Because the S2 measurements follow General Relativity so well, we can set stringent limits on how much invisible material, such as distributed dark matter or possible smaller black holes, is present around Sagittarius A*. This is of great interest in understanding the formation and evolution of supermassive black holes,” Guy Perrin and Karine Perraut, the French lead scientists in the research, said.

With ESO’s forthcoming Extremely Large Telescope, the team hopes to see much dimmer stars rotating even closer around the supermassive black hole.

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