Einstein's General Theory of Relativity, which he first wrote in 1936 has been proven by NASA's Hubble Space Telescope. The international research team is able to determine the mass of a white dwarf star using Einstein's theoretical method.
When Einstein wrote his theory in Science Magazine in 1936, he never thought that his theory can be confirmed. In his famous theory, Einstein predicted that everytime a light from a distant star passes by a closer object, the gravity will act as some kind of magnifying lens, brightening and bending the distant starlight. Facing the technology limit of his time, Einstein stated in his paper that "there is no hope of observing this phenomenon directly."
However, 80 years later, an international team of astronomers and astrophysicists is able to put Einstein's General Theory of Relativity into action. Kailash C. Sahu, an astronomer at the Space Telescope Science Institute has used the theory to measure the mass of a white dwarf star using the data from Hubble Space Telescope and the Einstein's General Theory of Relativity. Sahu has published his research paper in the Science Magazine vol. 356/6342, titled "Relativistic Deflection Of Background Starlight Measures The Mass of A Nearby White Dwarf Star."
Sahu used the Einstein's General Theory of Relativity in a gravitational microlensing measurement on the white dwarf Stein 2051B located 18 light-years away, as reported by Wired. They measured eight shifts in the apparent position of the stars using the Hubble Space Telescope which was deflected around Stein 2051B. Based on the measurement, taking from 2013 to 2015, they determined the mass of Stein 2051B to be about two-thirds of the Sun.
"Gravitational deflection of starlight around the Sun during the 1919 total solar eclipse provided measurements that confirmed Einstein’s general theory of relativity," a member of Sahu team said. We have used the Hubble Space Telescope to measure the analogous process of astrometric microlensing caused by a nearby star."