Sagittarius A*, the supermassive back hole at the center of the Milky Way galaxy, is surrounded by orbiting stars thanks to its mammoth gravitational pull. For decades, astronomers have been observing one specific star in this region, and new research proves once again, that Albert Einstein knew a thing or two about gravity. 

In a study published Thursday in the journal Astronomy & Astrophysics, researchers revealed for the first time that a star “dancing” around Sagittarius A* moves just as Einstein predicted with his general theory of relativity. The team of scientists studied the star for 27 years using European Southern Observatory’s Very Large Telescope in Chile’s Atacama Desert, hoping to unlock the mysteries of the gargantuan black hole at the heart of our galaxy.

Isaac Newton’s theory of gravity predicted a star would orbit the black hole in an elliptical manner, but researchers found S2’s orbit is actually shaped like a rosette around the black hole, which is located 26,000 light years from the sun. 

“Einstein’s General Relativity predicts that bound orbits of one object around another are not closed, as in Newtonian Gravity, but precess forwards in the plane of motion. This famous effect — first seen in the orbit of the planet Mercury around the Sun — was the first evidence in favor of General Relativity,”  co-author Reinhard Genzel said in a press release. 

Observations made with ESO’s Very Large Telescope (VLT) have revealed 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. This artist’s impression illustrates the precession of the star’s orbit, with the effect exaggerated for easier visualization.

ESO/L. Calçada

“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,” he continued. “This observational breakthrough strengthens the evidence that Sagittarius A* must be a supermassive black hole of 4 million times the mass of the Sun.” 

At its closest, S2 is less than 20 billion kilometers (about 12.5 billion miles) from Sagittarius A* — a distance that is 120 times the distance between the sun and the Earth — making it one of the closest stars ever observed orbiting the black hole. It was necessary for researchers to study the star for decades, as it only completes one orbit every 16 years.

The ever-changing motion of S2 exactly matches that predicted by Einstein’s theory. The rosette effect, known as Schwarzschild precession, had never before been measured for a star around a supermassive black hole, scientists said. 

This simulation shows the orbits of stars very close to the supermassive black hole at the heart of the Milky Way. One of these stars, named S2, orbits every 16 years and is passing very close to the black hole in May 2018. This is a perfect laboratory to test gravitational physics and specifically Einstein’s general theory of relativity.

ESO/L. Calçada/spaceengine.org

Not only does the research further confirm Einstein’s theory, it also provides crucial information about the area surrounding Sagittarius A*. 

“Because the S2 measurements follow General Relativity so well, we can set stringent limits on how much invisible material, such as distributed dark matter or possible smaller black holes, is present around Sagittarius A*. This is of great interest for understanding the formation and evolution of supermassive black holes,” said lead scientists Guy Perrin and Karine Perraut.

Using ESO’s new telescope, the team of scientists hopes to find stars orbiting even closer to the supermassive black hole. 

“If we are lucky, we might capture stars close enough that they actually feel the rotation, the spin, of the black hole,” co-author Andreas Eckart from Cologne University said. 

If they do find closer stars, astronomers would be able to measure both spin and mass, defining space and time around Sagittarius A*. “That would be again a completely different level of testing relativity,” Eckart said

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