A Star Dancing around a Supermassive Black Hole Has Proven Einstein Right

Captured by the European Southern Observatory, the star orbits the supermassive black hole in the center of our galaxy.
Fabienne Lang
The star orbiting the supermassive black hole European Southern Observatory

It's a beautiful day when a genius's prediction is confirmed, and today is such a day. A star orbiting the supermassive black hole at the center of our galaxy has just demonstrated Albert Einstein's prediction of general relativity is correct. 

Captured by the European Southern Observatory's (ESO) Very Large Telescope (VLT) over decades, the single star named S2 is seen to loop around and around the supermassive black hole in a spirograph way known as Schwarzschild precession

The research was published in Astronomy & Astrophysics.


Schwarzschild precession and black holes

S2's movement and formation is the first time a Schwarzschild precession is detected around a supermassive black hole, which unveils the fact that it holds true even when we watch the orbits of stars in the most gravitationally extreme environment. 

Moreover, the two-decades-and-a-half-long observations by ESO of S2 have perfectly matched up to general relativity's equations that predict the orbital changes. 

"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," explained astrophysicist Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany, and member of the GRAVITY Collaboration.

"This famous effect - first seen in the orbit of the planet Mercury around the Sun - was the first evidence in favor of general relativity. 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."

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Astronomers have been observing S2 since the 1990s and have used over 330 observations to ensure that the observed precession matches predictions made by general relativity. And it does. 

"After following the star in its orbit for over two and a half decades, our exquisite measurements robustly detect S2's Schwarzschild precession in its path around Sagittarius A*," said astrophysicist Stefan Gillessen of MPE.

Astrophysicists Guy Perrin and Karine Perraut of the Observatoire de Paris-Site de Meudon and the Observatoire de Grenoble in France, respectively, said "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."

What an exciting moment in astrophysics. 

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