Einstein was right, and this star dancing around a black hole proves it

Astronomers have observed a star “dancing” around the supermassive black hole at the heart of our galaxy, Sagittarius A*, in an orbit that confirms Einstein’s theory of general relativity.

Einstein’s theory of relativity overrode the previous model of gravity laid down by Newton. Newton’s theory stated that gravity is a force of attraction between two massive objects, and that this force acted instantaneously. But Einstein contradicted that, saying that gravity was not really a force but was rather a curvature of space-time. Although that distinction sounds abstract, it in fact has profound effects on the way we think about physics, especially in astronomy where we often look at the gravitational interactions of massive bodies.

According to the Newtonian model of gravity, the star moving around the supermassive black hole, called S2, should be in an orbit in the shape of an ellipse. But according to the Einsteinian model, the curvature of space-time caused by the enormous mass of the black hole means that the star should orbit in a rosette pattern, coming in closer to the black hole before moving away again in a new direction. The new observations confirm that S2 does in fact move in a rosette-type orbit.

a star orbiting the supermassive black hole
An artist’s impression illustrating observations made with ESO’s Very Large Telescope (VLT), revealing for the first time that a star orbiting the supermassive black hole at the center of the Milky Way moves just as predicted by Einstein’s theory of general relativity in an orbit is shaped like a rosette and not like an ellipse as predicted by Newton’s theory of gravity. ESO/L. Calçada

“This famous effect — first seen in the orbit of the planet Mercury around the Sun — was the first evidence in favor of General Relativity,” said Reinhard Genzel, Director at the Max Planck Institute for Extraterrestrial Physics, the leader of the observations. “One hundred years later we have now detected the same effect in the motion of a star orbiting the compact radio source Sagittarius A* at the center of the Milky Way.”

The observations were made using the Very Large Telescope over a period of 27 years. This large amount of time was required by the star completes an orbit only once every 16 years, even though at times it moves incredibly fast — up to 3% of the speed of light.

The research can tell us not only about gravity but also about how matter moves around black holes, and future projects using the upcoming Extremely Large Telescope could even reveal how fainter stars respond to the rotation of black holes.

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