London: After nearly 30 years of monitoring, scientists have found that a star orbiting the supermassive black hole at the centre of the Milky Way moves in a very strange way - just as predicted by Einstein's general theory of relativity.
Its orbit is shaped like a rosette and not like an ellipse as predicted by Newton's theory of gravity, said the study published in the journal Astronomy & Astrophysics.
The observations were made with Very Large Telescope (VLT) operated by ESO, the foremost intergovernmental astronomy organisation in Europe.
"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 favour of General Relativity," explained Reinhard Genzel, Director at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany.
"One hundred years later we have now detected the same effect in the motion of a star orbiting the compact radio source Sagittarius A-Star at the centre of the Milky Way.
"This observational breakthrough strengthens the evidence that Sagittarius A-Star must be a supermassive black hole of four million times the mass of the Sun," said Genzel, who is the architect of the 30-year-long programme that led to this result.
Located 26, 000 light-years from the Sun, Sagittarius A-Star and the dense cluster of stars around it provide a unique laboratory for testing physics in an otherwise unexplored and extreme regime of gravity.
One of these stars, S2, sweeps in towards the supermassive black hole to a closest distance less than 20 billion kilometres (one hundred and twenty times the distance between the Sun and Earth), making it one of the closest stars ever found in orbit around the massive giant.
At its closest approach to the black hole, S2 is hurtling through space at almost three percent of the speed of light, completing an orbit once every 16 years.
"After following the star in its orbit for over two and a half decades, our exquisite measurements robustly detect S2's Schwarzschild precession in its path around Sagittarius A-Star," said Stefan Gillessen of the MPE, who led the analysis of the measurements published in the study.
Most stars and planets have a non-circular orbit and therefore move closer to and further away from the object they are rotating around.
S2's orbit precesses, meaning that the location of its closest point to the supermassive black hole changes with each turn, such that the next orbit is rotated with regard to the previous one, creating a rosette shape.
General Relativity provides a precise prediction of how much its orbit changes and the latest measurements from this research exactly match the theory, said the study.
This effect, known as Schwarzschild precession, had never before been measured for a star around a supermassive black hole.