A star orbiting the supermassive black hole at the center of the Milky Way galaxy moves as Albert Einstein said it was going to move: rosette-shaped, not elliptical. For the first time, scientists were able to verify it, 65 years after his death and after 30 years of measurements.
Good news about progress in astrophysics: more than 100 years after Einstein will elaborate his general theory of relativity, scientists were able to verify that he was right and that indeed the stars dance in a very peculiar way around the supermassive black holes, or at least Sagittarius A *, the one at the heart of the Milky Way.
In 1915 Einstein realized that his newly formulated theory explained a strange oddity in Mercury’s orbit that seemed to spiral orbit around the Sun: the star’s path formed a kind of flower.
© CC BY 4.0 / European Southern Observatory
Artist’s rendering of the Schwarzschild precession
How to check Einstein’s theory?
At 26,000 light years from the Sun is the supermassive black hole Sagittarius A *; the dense cluster of stars around it “provide a unique laboratory for testing physics in an extreme and unexplored regime of gravity,” explains the architect of the program that began working 30 years ago to corroborate the theory, Reinhard Genzel, director of the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching (Germany), informs the statement from the European Southern Observatory (ESO).
There is the star S2, which is hurtling towards Sagittarius A * from a distance of less than 20,000 million kilometers (120 times the distance from the Sun to Earth), making it one of the closest stars ever found in orbit around the giant black hole.
In its closest approach to the black hole, S2 traverses space at almost 3% of the speed of light, completing an orbit once every 16 years. After following the star in its orbit for more than two and a half decades, they managed to corroborate that S2 has a precession movement: its location changes every time an orbital turn ends, so that the next orbit rotates with respect to the previous one, creating a rosette shape. It is worth remembering that most of the stars and planets have a non-circular orbit and, therefore, they approach and move away from the object around which they rotate.
The “rosette effect” (known as Schwarzschild precession) had been first seen in the orbit of the planet Mercury around the Sun; the first evidence in favor of general relativity raised by Einstein, but until now it had not been possible to measure.
