The Very Large Telescope (VLT) sees a star dance around the supermassive black hole. The observations prove Albert Einstein right, again.
A swarm of stars orbit Sagittarius A*, the behemoth black hole at the center of the Milky Way. Meanwhile, scientists have observed a star dance around it.
Astronomers have proved for the first time that the star S2, orbiting our central supermassive black hole, moves just as predicted by Einstein’s general theory of relativity. For this, they used the European Southern Observatory’s (ESO) Very Large Telescope (VLT).
The findings, published in the journal Astronomy & Astrophysics, came as a result of 27 years of observations of the star using a range of instruments, including the ESO’s VLT in the Atacama Desert in Chile. These observations enable scientists to unlock the mysteries of the mammoth black hole lurking at the heart of our galaxy.
The shape of the star’s orbit is more like a rosette rather than an ellipse as Newton’s gravity theory predicts.
“Einstein’s general relativity predicts that bound orbits of one object around another are not closed, as in Newtonian gravity, but precess forward 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,” study co-author Reinhard Genzel, director of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, said in a statement.
“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,” Genzel added. “This observational breakthrough strengthens the evidence that Sagittarius A* must be a supermassive black hole of 4 million times the mass of the sun.”
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The motion Genzel mentioned is known as the Schwarzschild precession. It describes a sort of rotation in an object’s elliptical orbit. Astronomers had never measured Schwarzschild precession in a star zooming around a supermassive black hole — until now.
Sagittarius A* supermassive black hole is about 26,000 light-years from the Sun.
S2 is one of the nearest stars we know in orbit around the massive giant. At its closest approach to the black hole, S2 speeds through space at almost three percent the speed of light. The star orbits Sagittarius A* once every 16 years. It sweeps in towards the black hole to the closest distance less than 20 billion kilometers. That’s one hundred and twenty times the distance between the Sun and Earth.
“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*,” says Stefan Gillessen of the MPE, who led the analysis of the measurements published today in the journal Astronomy & Astrophysics.
The observed precession matched the predictions of general relativity exactly. This could lead to further discoveries down the road, the researchers 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*,” team members Guy Perrin and Karine Perraut — of the Paris Observatory-PSL and the Grenoble Institute of Planetology and Astrophysics in France, respectively — said in the same statement.
“This is of great interest for understanding the formation and evolution of supermassive black holes,” they added.
“If we are lucky, we might capture stars close enough that they actually feel the rotation, the spin, of the black hole,” said study team member Andreas Eckart of Cologne University in Germany. “That would be again a completely different level of testing relativity.”
This research was presented in the paper “Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole” to appear in Astronomy & Astrophysics (DOI: 10.1051/0004-6361/202037813).