Illustration of the star S0-2 orbiting the supermassive black hole Sagittarius A* at the centre of the Milky Way galaxy. The star orbits the black hole once every 16 years. Observations over 24 years of the wavelengths of the star's light have shown a redshift of the light as its orbit brings it closer to the black hole. This proves a prediction made by Albert Einstein's theory of general relativity that light is deflected by extremely massive objects.