While some astronomer observing a star, called S2, that passed through the intense gravitational field of Sagittarius A*, the huge black hole at the heart of the Milky Way, By VLT, The Very Large Telescope, in Chile found evidence for Einstein’s prediction gravitational redshift.
When a particle of light (photons) climb out of a gravitational well like a black hole. The light’s wavelength gets prolonged. Due to this the wavelength to the red part of the light spectrum shift, hence it is called “redshift”
S2 is one member of a star cluster that surrounds Sagittarius A*. These stars reach mind-boggling speeds when they approach the black hole. The S2 comes very close to Sagittarius A* every 16 years.
On the 16th of May 2018, S2 passed close to the black hole. Astronomers were tracking its progress hour by hour when it was happening. As per their data shows, S2 passed by the black hole at a distance of just 17952 million km, it reached an astonishing orbital velocity of 8,000 km/s. That corresponds to about 2.7% of the speed of light.
The astronomers found that light from the star was indeed stretched to longer wavelengths by the very strong gravitational field of the black hole Sagittarius A*. The results were perfectly in line with the theory of general relativity.
The astronomers are continuing to observe S2 and its trajectory. It might lead us new findings about the extreme conditions around the Milky Way’s central black hole.
Gravitational redshift occurs because, in order to escape such gravitational well such as a black hole, particles of light (photons) must expend energy. However, at the same time, these photons must travel at a constant speed, i.e the speed of light. Therefore, the photons can’t lose energy by slowing down but must expend it in another way. This lost energy manifests itself as a shift towards the red end of the light spectrum.
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