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White Dwarf Makes Companion Look Bigger

Dead Star Warps Light of Companion Red Star, Astronomers Say


Science News


Apr. 5, 2013 — NASA's Kepler space telescope, in concert with Cornell-led measurements of stars' ultraviolet activity, has observed the effects of a dead star bending the light of its companion red star.


An artist's concept depicts a dense, dead star called a white dwarf crossing in front of a small, red star. The white dwarf's gravity is so great that it bends and magnifies light from the red star, causing it to appear bigger than it really is. (Credit: NASA/JPL-Caltech)

The findings are among the first detections of this effect -- a result predicted by Einstein's theory of general relativity -- in binary, or double, star systems.

The dead star, also called a white dwarf, is the burnt-out core of what used to be a star like our sun. It is locked in an orbiting dance with its partner, a small "red dwarf" star. While the tiny white dwarf is physically smaller than the red dwarf, it is more massive. When the white dwarf passed in front of its star, its gravity caused the starlight to observably bend and brighten.

"This white dwarf is about the size of Earth but the mass of the sun," said Phil Muirhead, Ph.D. '11, of the California Institute of Technology and lead author of the findings to be published April 20 in the Astrophysical Journal, titled "Characterizing the cool KOIs: A mutually eclipsing post-common envelope binary."

"It's so hefty that the red dwarf, though larger in physical size, is circling around the white dwarf," Muirhead continued.
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