Planets hiding in stars’ spiral arms?

U. WASHINGTON-SEATTLE (US) — A new image of a gas-and-dust disk around a sun-like star is the first astronomers have seen that displays structures that look like spiral arms.

The disk structures could hint at the presence of still-unseen planets around the star some 456 light years from Earth.

The image comes from research that is part of the Strategic Exploration of Exoplanets and Disks with Subaru project, a five-year-long study in the near-infrared spectrum of young stars and their surrounding dust disks using the Subaru Telescope atop Mauna Kea in Hawaii.


The work involves more than 100 scientists from 25 institutions, including John Wisniewski, a postdoctoral researcher in astronomy at the University of Washington.

“What we’re finding is that once these systems reach ages of a few million years, their disks begin to show a wealth of structure—rings, divots, gaps, and now spiral features,” Wisniewski says.

“Many of these structures could be caused by planets within the disks.”

The newly imaged disk surrounds SAO 206462, a star in the constellation Lupus. Astronomers estimate that the system is only about 9 million years old. The gas-rich disk spans some 14 billion miles, which is more than twice the size of Pluto’s orbit in our own solar system.

The Subaru image shows two spiral features arcing along an outer disk. Models indicate that a single embedded planet could produce a spiral arm on each side of a disk. The structures around SAO 206462 do not form a matched pair, suggesting the presence of two unseen worlds, one for each arm.

But processes unrelated to planet formation also could give rise to the spiral arms, and Wisniewski says the researchers will try to determine whether that is the case through further observation and theoretical modeling.

The research is led by Carol Grady of Eureka Scientific Inc. in Oakland, Calif. She presented the image this month at the Signposts of Planets meeting at NASA’s Goddard Space Flight Center in Greenbelt, Md.

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