The general theory of relativity is now 100 years old, first published by Albert Einstein in 1915. Since then, it has gone through a battery of astronomical tests, and has always come out unscathed. Now, astronomers are looking to put the theory through a rigorous set of standards – and they are looking towards the center of our own Milky Way as the testing ground.
Some physicists believe that the tests undertaken so far have been too weak. Typically involving a single star with a relatively weak gravitational field, the stars have bent or altered the speed of light very slightly. This is exactly what the general theory of relativity predicted. What if we apply the same standards to more extreme measures? This is where the super-massive black hole lurking at the center of our galaxy comes into play.
The task is being undertaken by two teams: The first at the University of California, Los Angeles (UCLA) led by Andrea Ghez, and the second at the Max Planck Institute for Extraterrestrial Physics (MPE) led by Reinhard Genzel. They will be looking at the orbit of stars that lean dangerously close to the edge of the super-massive, known as Sagittarius A*.
While initial testing began in the early 1990’s with the first infrared telescopes coming online, the big piece of the puzzle is yet to be built. Dubbed the Square Kilometer Array (SKA), it is expected to be fifty times more sensitive than any existing radio instrument.
However, observations are still certainly possible with current technology. The teams will be looking for two signs of relativistic effects: the star’s light shifting towards redder wavelengths and precession, whereby massive objects (such as the black hole) will gradually shift the star’s orbits. Combined, these two sets of data will help to confirm that Einstein’s theory works even under the harshest conditions.
With two groups of researchers looking for the same thing, only great results can be expected. “Everyone will be trying to get it. It’s a question of when do you believe your own measurements,” says Ghez, “It’s good for getting confirmation of your results. We push each other.”