Einstein proven right again as black hole gravity warps starlight
Einstein's theory of general relativity predicted plenty of amazing things, and to this day we're still making discoveries that back up his theories (or counter them). The latest such observation comes from the Max Planck Institute, where astronomers have watched how the supermassive black hole at the center of the Milky Way pulls and stretches the light from a star as it makes its closest pass.
To make their observations, the researchers used infrared instruments called Gravity, Sinfoni and Naco, which are part of the European Southern Observatory's Very Large Telescope. These were trained on the very center of our galaxy, where the supermassive black hole Sagittarius A* resides and interacts with a group of stars that orbit around it at high speed.
One star in particular, dubbed S2, caught the team's eye. This star orbits the black hole once every 15 years, and it was due to make its closest pass on May 19 this year. The intense gravitational influences it would be subjected to made this a perfect opportunity to test several different theories of gravity.
The team used Gravity and Sinfoni to measure the position and velocity of S2, and combined that with data gathered during a previous observation of the star's close passage. These results were then compared to predictions made by Newtonian gravitational physics, the general theory of relativity, and other theories of gravity, to see which lined up the closest to the actual observations.
Sure enough, Einstein won out. The results were in "excellent agreement" with what would be expected under general relativity, and inconsistent with a simpler Newtonian model. The key observation was of an effect called gravitational redshift, where the black hole's influence on a star's light can be clearly seen.
Black holes get their name form their inky black appearance, which is famously caused by the fact that after a certain point, their gravitational pull is so powerful that light itself cannot escape. Although S2 is far enough away that it can avoid being swallowed up, its light is still slowed down somewhat by the black hole. That "stretches" out the wavelengths and makes the light appear more red than it otherwise would be – a phenomenon known as gravitational redshift, which was predicted by Einstein's general relativity over 100 years ago.
The team plans to continue observing interactions between the star and the supermassive black hole. The research was published in the journal Astronomy & Astrophysics.
An artist's rendition of the gravitational redshift effect can be seen in the animation below.
Source: Max Planck Institute