The Stars of EF Eri

The Stars of EF Eri

This artist's concept depicts subtle mass transfer between the stars of EF Eridanus, nicknamed EF Eri for short.

Located 300 light-years away, EF Eri is binary (two star) cataclysmic variable system. In this system a white dwarf, or a dead star with approximately 60 percent of our Sun's mass crammed into an Earth-size ball, is orbiting another low mass star. Astronomers say that more than 1 million Earths can fit inside our Sun.

Over the years, gravitational interactions between the two stars allowed EF Eri's white dwarf to pull so much material from its partner star, that the companion no longer resembles any known star type.

Until NASA's Galaxy Evolution Explorer noticed a "hot spot" on the pole of EF Eri's white dwarf in 2004, astronomers believed that all mass transfer between the two stars halted in 1997. Scientists now suspect that there is subtle mass transfer occurring in the system, where the white dwarf's magnetic fields are pulling in material from its companion star's stellar winds.

In this image, the white dwarf is represented as the little white ball to the lower left. The green lines represent the white dwarf's magnetic fields, and the white wisps are the winds from the companion star. Material from the companion stars' winds are being picked up by the white dwarf's magnetic fields, and funneled into the dwarf's "north" and "south" poles. Astronomers think that the location of the bright hot spot on the white dwarf's southern pole indicates that the star is tilted, with its southern end facing the companion star. The partner star is represented as the large yellow ball to the right.

Credit: NASA/JPL-Caltech/T. Pyle

Release Date

December 13, 2006

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