Europe’s foremost astronomy organisation, ESO, has proved Einstein's General Relativity is precisely correct!
Observations made with the European Southern Observatory’s Very Large Telescope (VLT) placed in the Chilean desert have revealed for the first time that a star orbiting the enormous black hole in the middle of the Milky Way moves just as predicted by Einstein's general theory of relativity.
The study published in the journal Astronomy & Astrophysics would enable scientists to unlock the mysteries of the mind-boggling big bunch of stars in our galaxy.
Astronomers, who have been following the movements of one particular high-speed star in our galaxy for nearly three decades, have found its orbit is shaped like a rosette and unlike an ellipse as proposed by Newton's theory of gravity.
"Our previous result has shown that the light emitted from the star experiences General Relativity. Now we have shown that the star itself senses the effects of General Relativity," says Paulo Garcia, a researcher at Portugal's Centre for Astrophysics and Gravitation and one of the lead scientists associated with the ESO project.
The star S2, which is part of a dense cluster of stars around Sagittarius A-Star (Sagittarius A* or Sgr A*), was observed sweeping in towards the mysterious monster 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.
Most stars and planets have a non-circular orbit and therefore move closer to and further away from the object they are orbiting 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. This effect, known as Schwarzschild precession, had never before been measured for a star around a supermassive black hole.
Sagittarius A*, the supermassive black hole, near the border of the constellations Sagittarius and Scorpius, is located 26 000 light-years from the Sun.
"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. 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 centre 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 architect of the 30-year-long programme that led to this discovery.
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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*," said Stefan Gillessen of the MPE, who led the analysis of the precise measurements.
The study with ESO's VLT also helps scientists learn more about the vicinity of the supermassive black hole at the centre of our galaxy. "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 for understanding the formation and evolution of supermassive black holes," say Guy Perrin and Karine Perraut, the French lead scientists of the project.
With ESO's upcoming Extremely Large Telescope, the team believes that they would be able to see much fainter stars orbiting even closer to the supermassive black hole. "If we are lucky, we might capture stars close enough that they actually feel the rotation, the spin, of the black hole," says Andreas Eckart from Cologne University, another of the lead scientists of the project. This would mean astronomers would be able to measure the two quantities, spin and mass, that characterise Sagittarius A* and define space and time around it. "That would be again a completely different level of testing relativity," said Eckart.