In what could be the first time, a measurement of the strength of general relativistic effects has been achieved from stars orbiting close to a supermassive black hole. Tested against a strong gravitational field which holds even under extreme conditions, this recent research might support the effects of predictions made by Einstein’s general relativity.
Shrouded in a cloud of gas and dust in the center of our galaxy is the black hole is known as Sagittarius A* (Sgr A*), the closest supermassive black hole which had been deduced to have a mass four million times more massive than our Sun. This giant monster is surrounded by a group of stars orbiting at high speed around the black hole’s strong gravitational field which makes it an ideal environment to test the general theory of relativity.
A group of astronomers in Germany and the Czech Republic had been tracking the movements of three stars orbiting near Sgr A*. Using data from the ESO’s Very Large Telescope (VLT) in Chile and other Telescope for the past 20 years, astronomers applied a new analytical technique, which deviates the predictions of classical physics. Instead, it hints support of the subtle effects predicted by Einstein’s general relativity.
The closest known star to Sgr A*, known as S2, showed hints of a small change in motion, indicating relativity effects. It’s a slight change, about one-sixth of a degree in the orientation from the orbit, and a few percent of its elliptical orbit’s shape.
“To determine relativistic effects for S2,” Andreas Eckart team leader at the University of Cologne realized during their analysis that “one definitely needs to know the full orbit to very high precision.”
The VLT’s near-infrared adaptive optics made the accuracy of the positional measurements possible, which was essential for the study. The accuracy of the data is essential even when the S2 star was further away from the black hole as it provided the team with an accurate determination of the ellipse of the orbit.
In an upcoming big event in the middle of 2018, astronomers look forward to observing the galactic center where the star will take its orbit close to the black hole, which only happens once every 16 years. Its distance would be about four times between the sun and Neptune. Installed on the VLT Interferometer is the GRAVITY instrument, used to measure the orbit of the S2 star precisely. The instrument is already making highly precise measurements of the galactic center and it is expected to reveal relativistic effects clearly. It could also allow astronomers to detect deviations from general relativity, revealing new physics.
Vladimir Karas, from the Academy of Sciences in Prague, exclaims that “this opens up an avenue for more theory and experiments in this sector of science.”
[Featured Image by ESO/M. Parsa/L. Calçada]