One of the great unsolved problems in modern physics is the nature of gravity. Since Einstein first published the general theory of relativity over a century ago, it has proven to be a very accurate model of the solar system and the cosmos. Repeated experiments have confirmed its predictions in the form of planetary orbits, gravitational lensing, and high precision measurements of time and frequency on the Earth and in orbit. So far no deviations from the predictions of general relativity have ever been detected.

However scientists have also been limited in the systems that they can study. Precise gravitational measurements can be made on the surface of the Earth or in orbit around the Earth, but our planet is rather small and boring. And while we can study the effects of gravitational lensing by observing distant galaxies, these effects are still caused by gravitational effects over long distances. We have not yet been able to measure the effects of general relativity in high energy, high density systems in which extreme gravitational fields are present. It is possible that general relativity will break down in these regions, and in fact we know from theoretical work in the theory of quantum gravity that general relativity cannot describe all objects in our Universe. At some point the theory will need to be replaced by something better, just as general relativity itself replaced Newtonian gravity.

And this coming Spring, a cosmic coincidence could provide one of the most powerful tests of the general theory of relativity. 

At the center of our own Milky Way galaxy, there exists a supermassive black hole. It is so massive that all of the stars and planets in our galaxy rotate around it, just as the planets in our solar system rotate around the Sun. And the gravitational field at its surface is so strong, that it may not obey the usual laws of general relativity. 

Near the center of the Milky Way there is also a dense collection of stars known as the S-stars. They are young, active stars whose formation and existence in such a hostile environment remains a mystery to astrophysicists. One of these stars, S0-2, is on course to pass very close to the supermassive black hole in the next few months, and when it does it will provide an excellent opportunity for astronomers to test the general theory of relativity.

Astronomers have carefully measured the precise wavelengths of light being emitted by this star, and will continue to do so through the rest of the year. According the general theory of relativity, these wavelengths will be redshifted, or stretched out by the warping of space near the event horizon of the black hole. By measuring the wavelength of the light that we receive in terrestrial telescopes, scientists will be able to compare the effects of the black hole's gravity on the star to the predictions of general relativity. And if they differ by any significant amount, it would indicate the first experimental evidence of a new, modified form of gravity - and perhaps even start to provide data on the nature of quantum gravity.

If the astronomers are able to find such deviations from the accepted models of gravity, then they expect to follow it up with further measurements of other stars near the galactic core and collect more data. If not, then it will tell us that general relativity is a valid theory even in extreme environments such as this one.

Either way it will be an important test of the general theory of relativity, and should result in some amazing new data that will be studied for years to come!