Einstein was right: Astronomers confirm key theory

Paris : A consortium of astronomers said yesterday they had for the first time confirmed a prediction of Albert Einstein’s theory of general relativity by observing the gravitational effects of a supermassive black hole on a star zipping by it.

The German-born theoretical physicist had posited that large gravitational forces could stretch light, much like the compression and stretching of sound waves we perceive with the change of pitch of a passing train. Researchers from the GRAVITY consortium led by the Max Planck Institute for Extraterrestrial Physics realised that they had a “perfect laboratory” to test Einstein’s theory with the Sagittarius A* black hole in the centre of the Milky Way.

Black holes are so dense that their gravitational pull can trap even light, and the supermassive Sagittarius A* has mass four million times that of our sun, making it the biggest in our galaxy. Astronomers followed the S2 star as it passed close to the black hole on May 19 at a speed in excess of 25 million kilometres (15.5 million miles) per hour. They then calculated its velocity and position using a number of instruments and compared it with predictions made by Einstein that the light would be stretched by the gravity in an effect called gravitational redshift. Newtonian physics doesn’t allow for a redshift.

“The results are perfectly in line with the theory of general relativity” and are “a major breakthrough towards better understanding the effects of intense gravitational fields,” said the research team.