The stars used in the observations are so close to the black hole that they move at 1 or 2 percent the speed of light, Eckart said, and they approach to within only about 100 times the Earth-sun distance of the black hole itself, which is quite close by galactic standards, he said. (Pluto averages about 39 times the Earth's distance from the sun, which is about 93 million miles or 150 million kilometers).
Using orbiting bodies to show relativistic effects is not new; observations of the planet Mercury in the 19th century showed that its movements deviated from what Isaac Newton's theory of gravity predicted. At first, astronomers thought they had evidence of another planet, which they dubbed Vulcan. Einstein was able to show in 1915 that relativity could explain the deviation.
Mercury's motions proved Einstein correct, but the sun's gravity is weak compared to that of a supermassive black hole. This is why Eckart and his team set out to see if Einstein's theory held up in a more extreme environment. While gravitational lensing, the bending of light by massive objects, shows that massive objects bend space, the recent research is the first time anyone has taken precise measurements of any object orbiting so close to a black hole.
The measurement itself is not as precise as it might be, Eckart said. Future work will get a better read on the stars' positions and narrow down the result. He said one plan is to get better spectrographic measurements, which would reveal S2's movement more precisely.
Original article on Space.com.
In First, Einstein Relativity Experiment Used to Measure a Star's Mass
How a Total Solar Eclipse Helped Prove Einstein Right About Relativity
Einstein's Theory of Special Relativity