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takyon [soylentnews.org] writes:

Astronomers have used the Hubble Space Telescope to confirm Einstein's General Theory of Relativity and measure a star's mass by examining the slight gravitational microlensing [sciencemag.org] it caused on the light of a star behind it:

Weighing a star is hard. In fact, binary stars are the only ones scientists can directly gauge, because their orbits around each other reveal their masses. Now, a team of astronomers has succeeded in measuring the mass of an isolated star using a technique first suggested by Albert Einstein in 1936. The method exploits the fact that a large mass, like a star, can bend the path of light. Although the effect is tiny, measuring the deflection can reveal the mass of the light-bending star.

[...] [A] team of astronomers from the United States, the United Kingdom, and Canada had a hunch that the keen-eyed view of the Hubble Space Telescope might be able to detect such a shift. They started by looking for stars that might be coming into alignment, and found that Stein 2051 B—a white dwarf just 18 light-years from Earth—was due to pass almost directly in front of another star in March 2014. When it did, the team captured the slightest shifts in position of the background star. That shift let the team calculate that Stein 2051 B's mass is about two-thirds the mass of the sun [sciencemag.org] [open, DOI: 10.1126/science.aal2879] [DX [doi.org]], 0.675 solar masses, they report today in Science.

Also at Space.com [space.com]:

The scientists behind the new work said no one, before now, has ever used the displacement of a background star to calculate the mass of an individual star. In fact, there is only one other example of scientists measuring this displacement between individual stars: During the 1919 total solar eclipse [space.com], scientists saw the sun displace a few background stars. That measurement was possible only because of the sun's proximity to Earth.

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