How to weigh a star using gravitational lensing

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Astronomers recently tapped Einstein's concept of gravitational lensing to determine the weight of a distant star. Watch and learn how this concept came to be and how it works.

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Here's some exciting space news, astronomers have used the Hubble Telescope and a technique pioneered by Albert Einstein to weigh a white dwarf star for the first time. So in 1916, Einstein said that a massive object like a star would actually warp the fabric of space-time, and what that means is that a ray of light going past the star would actually get bent and move in a different path than it was before. In 1936, a Czech engineer named Mandl came and knocked on Einstein's door and asked him to do a little calculation. He said, "What would happen if a star passed in front of another star?" And Einstein really didn't want to do it. He was kind of busy, but he felt sorry for him and he did the calculation and wrote a paper for Science. A very short paper saying: if one star passed in front of another star, the distant star would be magnified and distorted by this gravitational lensing effect. And today, gravitational lensing is one of the most powerful tools in astronomy. People use it to measure the size of the universe and to map out dark matter and to find distant galaxies they couldn't find otherwise because they were too dim. What people at space telescope have done is watch as a distant ordinary star passed behind a white dwarf. It was distorted just as Einstein said it would and by looking at the exact distortion they were able to calculate how much the white dwarf was distorting space-time and therefore what its mass was. Which turns out to be 2/3 the mass of the Sun, more or less, which is what the theory said but still, it's good to know. So once more, we have Einstein to thank for yet another discovery even though he died way back in 1955.
This is Mike Lemonick for Scientific American. Please take the time to subscribe to our YouTube channel.