File:Hubble Measures Deflection of Starlight by a Foreground Object (Artist's Illustration) (2023-004).png

English: This artist's illustration shows how the gravity of a foreground white dwarf star warps space and bends the light of a distant star behind it. Astronomers using NASA's Hubble Space Telescope have for the first time directly measured the mass of a single, isolated white dwarf (the surviving core of a burned-out Sun-like star) – due to this optical trick of nature. The greater the temporary, infinitesimal deflection of the background star's image, the more massive the foreground star is. (This deviation is so small that it is equivalent to observing an ant crawl across the surface of a quarter from 1,500 miles away.) Researchers found that the dwarf is 56 percent the mass of our Sun. This effect, called gravitational lensing was predicted as a consequence of Einstein's theory of general relativity from a century ago. Observations of a solar eclipse in 1919 provided the first experimental proof for general relativity. But Einstein didn't think the same experiment could be done for stars beyond our Sun because of the extraordinary precision required.