Fomalhaut Is Triple

By Ken Croswell

Published on ScienceNOW (October 3, 2013)

Credit: NASA, ESA; P. Kalas and J. Graham (UC Berkeley) and M. Clampin (NASA/GSFC); (inset) Eric Mamajek (University of Rochester) et al.

Located 25 light-years from Earth and shining by its lonesome in the southern sky on October evenings, Fomalhaut is sometimes called "the solitary one." It's a white A-type star, somewhat hotter than the Sun, and the eighteenth brightest star in the night; it harbors a dusty disk (main image) and a planet whose existence is controversial. Now astronomers report that a little red star (inset, circled), discovered decades ago 5.67 degrees northwest of Fomalhaut, shares the same distance and motion through space. Thus, as the scientists will announce in a future issue of The Astronomical Journal, the dim red sun probably revolves around the bright white star, even though the two are separated by a whopping 2.5 light-years of space, which is more than half the distance between the Sun and Alpha Centauri, the nearest star system to our own. The astronomers calculate that completing a single orbit takes the red dwarf roughly 20 million years. Fomalhaut possesses another distant companion, an orange dwarf named Fomalhaut B, so the discovery means this famous star is a triple system with two of the farthest-flung stellar companions ever seen. And that suggests that widely spaced star systems are more common than astronomers previously thought. Meanwhile, the little red star, which bears the prosaic name LP 876-10, is in for an upgrade: the researchers recommend it be rechristened Fomalhaut C.

Ken Croswell earned his Ph.D. in astronomy from Harvard University and is the author of The Alchemy of the Heavens and The Lives of Stars.

"An engaging account of the continuing discovery of our Galaxy...wonderful." --Owen Gingerich, The New York Times Book Review. See all reviews of The Alchemy of the Heavens here.

"A stellar picture of what we know or guess about those distant lights."--Kirkus. See all reviews of The Lives of Stars here.

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