From ABC Science, 8 June 2017:
Astronomers have used the gravitational warping of light, predicted by Einstein nearly a century ago, to measure the mass of a distant star for the first time.
The team, led by Kailash Sahu of the Space Telescope Science Institute in Baltimore, measured the mass of a white dwarf star called Stein 2051 B as it passed in front of another more distant star — an event Einstein thought would be impossible to observe.
The findings, publishing in today’s edition of Science, will help us understand more about these small dense stars and the ultimate fate of our Sun, which will become a white dwarf star when it burns out.
Dr Sahu relied on Einstein’s idea that the gravity of an object can bend and magnify rays of light.
According to Einstein’s general theory of relativity, an object passing in front of another bright object would bend the light of the more distant object and cause it to appear to move from its original position.
In this “gravitational lensing”, the distance apparently travelled by the background object depends on the mass of the object in front, which is curving the light. Read more.