For more than four hundred years, astronomers have used telescopes to study the
great variety of stars in our galaxy. Millions of distant suns have been
catalogued. There are dwarf stars, giant stars, dead stars, exploding stars,
By now, you might suppose that every kind of star in the Milky Way had been
seen. That's why a recent discovery is so surprising. Researchers using the
Subaru telescope in Hawaii have found a star with spiral arms.
The name of the star is SAO 206462, we'll call it "462" for short. It's a young
star more than four hundred light years from Earth in the constellation Lupus,
462 attracted attention because it has a circum-stellar disk, that is, a broad
disk of dust and gas surrounding the star. Researchers strongly suspected that
new planets might be coalescing inside the disk, which is about twice as wide as
the orbit of Pluto. When they took a closer look at 462 they found not planets,
Astronomers have seen spiral arms before: they're commonly found in pinwheel
galaxies where hundreds of millions of stars spiral together around a common
core. Finding a clear case of spiral arms around an individual star however, is
surprising. The arms might be a sign that planets are forming within the disk.
"Detailed computer simulations have shown us that the gravitational pull of a
planet inside a circum-stellar disk can perturb gas and dust, creating spiral
arms," says Carol Grady, an astronomer with Eureka Scientific, Inc., who is
based at NASA's Goddard Space Flight Center. "Now, for the first time, we're
seeing these dynamical features."
Grady revealed the image to colleagues on October 19th at a meeting at Goddard
entitled Signposts of Planets. Theoretical models show that a single embedded
planet may produce a spiral arm on each side of a disk. The structures around
462, however, do not form a matched pair, suggesting the presence of two unseen
worlds, one for each arm.
Grady's research is part of a five-year international study of newborn stars and
planets using the giant 8.2 meter Subaru Telescope. Operated by the National
Astronomical Observatory of Japan, Subaru scans the heavens from a perch almost
14,000 feet above sea level at the summit of the Hawaiian volcano Mauna Kea.
From there it has a crystal-clear view of innumerable young stars and their
planet-forming disks throughout the Milky Way.
"What we're finding is that once these systems reach ages of a few million
years, that's young for a star, their disks begin to show all kinds of
interesting shapes," says John Wisniewski, a collaborator at the University of
Washington in Seattle. "We've seen rings, divots, gaps, and now spiral features.
Many of these structures could be caused by planets moving within the disks."
However, it is not an open and shut case. The research team cautions that
processes unrelated to planets might give rise to these structures. Until more
evidence is collected, or until the planets themselves are detected, they can't
be certain. One thing is for sure: The Milky Way is still full of surprises.
For more news from our home galaxy, and beyond, visit science.nasa.gov.