Astronomers have directly measured the mass of a single star the
first time such a feat has been accomplished for any solitary
star other than our own Sun. The measurement has been done on a
small red star located some 1,800 light-years from Earth.
Knowing the masses of stars is important in understanding
stellar evolution. Until now, scientists could only determine
the masses of stars that are members of binary-star systems by
applying Newton's laws of gravity to measurements of the stars'
orbits around their center of gravity. The new measurement used
Einstein's theory of relativity, combined with a large-scale
program using ground-based telescopes, and the exquisite
resolution of NASA's Hubble Space Telescope. The dim red star
first caught astronomers' attention in 1993, when it passed
directly in front of a much more distant star, producing a
phenomenon called gravitational microlensing. Microlensing,
which was predicted by Einstein's theory of general relativity,
occurs because of the warping of space ar