By analyzing the extraordinary gravity of the huge black hole at the center of the Milky Way on a star nearby, astronomers have shown that Einstein's notions of space and time are still the best description of how gravity works
According to Einstein's general theory of relativity, gravity is the result of how the mass deviates space and time. The larger the mass of an object, the stronger its appeal.
Scientists have largely tested the predictions of general relativity in relatively weak gravitational fields such as those on Earth and in the solar system. In the presence of much stronger gravitational fields ̵
"Einstein is right, at least for now," said Andrea Ghez, co-principal author of the research and astronomy professor at the University of California at Los Angeles, in a statement. "His observations are in line with Einstein's theory of general relativity, but his theory definitely shows vulnerability, it can not fully explain gravity in a black hole, and eventually we need to move beyond Einstein's theory to a more comprehensive theory of gravitation that explains what a black hole is .
Related: Images: Black Holes of the Universe
In the new study, astronomers studied the supermassive Black Hole Sagittarius A *, often abbreviated Sgr A *. This giant, located in the center of the Milky Way, has about 4 million times the mass of the Sun and a diameter of about 23.6 million kilometers.
The scientists observed the star S0-2 in 2018 when he emerged his closest approach to Sagittarius A * during his 16-year orbit. The star approached 120 astronomical units (AU) from the black hole – an AU is the average distance between Earth and Sun, about 93 million miles (150 million kilometers) – and moved at a speed of 2.7% of the speed of light.
With the Keck Observatory, the Gemini Observatory and the Subaru Telescope in Hawaii, astronomers were able to track the full orbit of S0-2 in 3D. They combined this data with measurements from the last 24 years.
The researchers studied a prediction of the general theory of relativity, known as "gravitational redshift," in which gravity can distort light. Just as an ambulance siren for humans sounds higher and lower as the vehicle approaches them, light falling on a gravitational field is shifted to the blue end of the spectrum, while light exiting a gravitational field is reddened or redshifted.
"These measurements signal the beginning of an era in which we can finally test the nature of gravity by orbiting the stars around the supermassive black hole at the center of our galaxy," said study leader Tuan Do, an astrophysicist at the University of California in Los Angeles, told Space.com:
"This has been theorized for a long time, but it's really exciting that we can finally make it," Do added. "This is a milestone in this area the way to the future, stronger tests of general relativity and other theories of gravity."
The light spectrum demonstrated by S0-2 showed that the redshift due to the extreme gravity of Sagittarius A * was consistent with general relativity. It was "amazing" to see the predictions of General Relativity "work, although black holes, much less supermassive black holes, were not even known when Einstein developed his theory," Do said.
2 is the first of many Studies on the general theory of relativity, which the scientists want to perform on stars near Sagittarius A *. One such target is S0-102, which has the shortest orbit among the more than 3,000 stars near the supermassive black hole and takes 11.5 years to circle it.
Scientists have detailed their findings online today (July 25) in the journal Science.
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