Star spotted speeding near black hole at centre of Milky Way

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Einstein's theory still doesn't explain everything about the universe, which is why scientists keep testing it, but they acknowledge he's won this round.

In a paper published on July 26, researchers demonstrated that "gravitational redshift"-a prime component of the Einstein theory around gravity and space/time-is definitely happening near the massive black hole at the center of the Milky Way. So it's very important in astronomy to also check that those laws are still valid where the gravitational fields are very much stronger".

The close approach of a star near a supermassive black hole at the center of our Galaxy provided the first opportunity to directly test General relativity in extreme gravitational fields.

Black holes are so dense that their gravitational pull can trap even light, and the supermassive Sagittarius A* has mass four million times that of our sun, making it the biggest in our galaxy. Furthermore, the adjustment in the wavelength of light from S2 concurs unequivocally with that anticipated by Einstein's theory of general relativity.

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Since the 1990s, a team of researchers led by Reinhard Genzel from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany has been tracking the journey of one of these stars called S2.

"Our first observations of S2 with GRAVITY, about two years ago, already showed that we would have the ideal black hole laboratory", said Frank Eisenhauer, principal investigator of GRAVITY and the SINFONI spectrograph.

Star spotted speeding near black hole at centre of Milky Way
A distant black hole just proved Albert Einstein was right

The new measurements clearly reveal an effect called gravitational redshift.

The European Southern Observatory, whose Very Large Telescope in Chile was used to make the observations, had watched S2 pass by Sagittarius A* in 2016 but the instruments it was using then were not sensitive enough to detect the gravitational redshift. All these belong to the ESO's Very Large Telescope, were constructed under the leadership of the Max Planck Institute for Extraterrestrial Physics (MPE), and scrutinise the sky in an infrared light. Thus, the precise measurements of the position of the star allowed the scientists to highlight the effect of gravitational reddening predicted by the theory of Einstein. One of these stars, named S2, orbits every 16 years and is passing very close to the black hole in May 2018. "In this way, we could follow the star on its orbit to an extremely high degree of precision, and could ultimately provide evidence of the gravitational redshift in the spectrum of S2". Einstein's 100-year-old theory of relativity is that according to Einstein, the light from stars would be stretched to longer wavelengths by the extreme gravitational field of a black hole and that the star would appear redder.

Other instruments at the observatory measured the speed at which S2 traveled toward or away from Earth while it swung by Sgr A*. Several of its components have been proven over the years, but this is the latest.

"This is the second time that we have observed the close passage of S2 around the black hole in our galactic centre".

"It's really the first time a [gravitational red shift] has been seen in such a clear fashion on an object that is moving", said Paumard.

Artist's conception illustrating the star's trajectory over the past few months.

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