The movement of a star around a black hole confirms Einstein’s theory

Observations made with the VLT Very Large Telescope have shown for the first time that a star orbiting a supermassive black hole at the center of the Milky Way is moving exactly as predicted by Einstein’s general theory of relativity. The orbit of the star makes a precession, forming a kind of “rosette”, and not an ellipse, which would correspond to Newton’s theory of gravity. This result is based on measurements carried out over more than 30 years.

Einstein’s general theory of relativity is the main theory of gravity in modern physics. One of her predictions is that the orbit of an object moving in the gravitational field of another object is not closed, as in the case of Newtonian gravitation, but makes a precession in the orbital plane in the direction of motion. This effect, known as the Schwarzschild precession, was first observed in the orbit of Mercury around the Sun and was once the first observational confirmation of Einstein’s theory. And now, after a hundred years, it was possible to register it for the motion of a star around a black hole.


Illustration of the precession of the star’s orbit with an exaggerated effect for better visualization

The so-called Sagittarius A * object, a compact radio source located 26,000 light-years from the Sun in the center of our Milky Way galaxy, acted as a massive black hole. According to scientists, the mass of this object reaches 4 million times the mass of the Sun, and there is every reason to believe that it is exactly a black hole.

Around Sagittarius A * there is a dense star cluster, one of the stars of which, S2, at the closest point of its orbit approaches the supermassive black hole at a distance of less than 20 billion km (this is only one hundred twenty times the distance between the Sun and the Earth). S2 is one of the closest stars to a black hole. At the point of closest approach, it moves at a speed of almost three percent of the speed of light, and makes a full orbital revolution in 16 years.

Most of the stars and planets move along elongated orbits and are either closer to the central object or further away from it. At the same time, Einstein’s theory of gravity predicts that the orbit should perform precession, that is, the position of the points of its smallest and largest distance from the gravitating center changes with each revolution: each next orbit rotates relative to the previous one by a certain angle. General relativity predicts exactly how much the orbit should shift, and the latest measurements made for S2 are exactly in line with this theory.

In addition, this measurement allowed us to learn more about the surroundings of the black hole at the center of our Galaxy. The motion of the S2 star fits well with the general theory of relativity, and this makes it possible to impose more stringent restrictions on the amount of dark matter in the vicinity of Sagittarius A *.


Computer simulation of the orbits of stars in the immediate vicinity of a supermassive black hole in the center of the Milky Way

Computer simulation of the orbits of stars in the immediate vicinity of a supermassive black hole in the center of the Milky Way


Source: ESO Telescope Observes Star Dance Around Supermassive Black Hole and Confirms Einstein’s Right // ESO

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