Albert Einstein’s theory of general relativity holds up well, even around the supermassive black hole in the center of our galaxy.
A group of European astrophysicists from the European Southern Observatory’s Gravity Consortium used observations from ESO’s Very Large Telescope, located in Chile, to highlight the effects of general relativity on the movement of a star (S2) passing through the intense gravitational field of Sagittarius A*, the black hole in the center of the Milky Way.
“More than 100 years after his article putting the equations of general relativity, Einstein shows that he is once again right, in a much more extreme laboratory than he could imagine,” says Gravity Consortium.
Sagittarius A* (Sgr A*) is located in the heart of our galaxy 26,000 light-years from Earth. Its mass is equivalent to no less than 4 million times that of the Sun. In its neighborhood is a cluster of stars that reach vertiginous speeds as they approach the massive object.
In his theory of general relativity, Einstein describes the influence of matter on the motion of the stars. In this case, it is the influence of the black hole on the stars that surround it. In this context, Sgr A* is an ideal environment for testing Einstein’s theory of relativity, since the stars that surround it are in the most intense gravitational field of the galaxy.
The Gravity Consortium scientists followed a star (S2) in particular of the Sgr A* system before and after it passed close to the black hole on May 19, 2018.
The precision reached by the telescope instruments was 50 microseconds angle, the angle at which a tennis ball resting on the moon would be seen from the Earth. Thanks to this precision, the movement of the star could be detected hour by hour as close as possible to the black hole. When the star was only 120 times the Earth-Sun distance of Sgr A*, its orbital speed reached 8000 km/s or 2.7% of the speed of light.
According to the researchers, these conditions are extreme enough for the star to suffer the effects of general relativity. Thus, the precise measurements of the position of the star allowed the scientists to highlight the effect of gravitational reddening predicted by the theory of Einstein.
“When the star approaches the black hole, it appears redder than it actually is, because there is a shift of wavelengths towards the red, because of the very strong gravitational attraction of the black hole,” says Guy Perrin, of the Paris Observatory.
This is the first time that this effect is measured for the gravitational field of a black hole. Thus, these results represent a major breakthrough to better understand the effects of intense gravitational fields. The detection of changes in the trajectory of the star under the effect of gravity is expected in a few months and could provide information on the mass distribution around the black hole.