Four’s a crowd

From Austin, Texas, at a meeting of the American Astronomical Society

Many stars reside in pairs, but now astronomers have discovered a rare, closely spaced quartet. Four stars that lie just south of the constellation Aquarius orbit each other within an area smaller than Jupiter’s orbit around the sun, Evgenay Shkolnik and her colleagues at the University of Hawaii, Manoa, in Honolulu report.

While monitoring several hundred low-mass stars, the team noticed something odd about a star system called BD-22°5866, 166 light-years from Earth. Spectra taken with the Keck I and Canada-France-Hawaii telescopes atop Hawaii’s Mauna Kea revealed that what appeared to be a single point of light was actually four distinct stars in two tightly coupled pairs. Stars in one of the pairs orbit each other at a maximum distance nearly equal to Jupiter’s separation from the sun, while the stars in the other duo are in a much tighter pas de deux. Only about 1 in 2,000 stars resides in such close quarters, Shkolnik’s team estimates.

The stars are too tightly grouped to have been born that way, the team calculates. The researchers instead attribute the crowded configuration to a single gaseous disk that may have enveloped all four stars when they were young and farther apart. Such a disk—common around newborn stars—could have pulled the stars close together within 100,000 years of their birth, the team suggests.

Shkolnik and her collaborators are now monitoring the star system to determine whether any of its members eclipse each other. Eclipses would reveal further details about the mass, size, and other properties of the quartet. That, in turn, could provide new insight about the formation and evolution of other stars with multiple partners.

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