Wednesday, June 10, 2009
Astronomers are announcing today that a sequence of images
collected with the Smithsonian's Submillimeter Array (SMA) clearly
reveals the presence of a rotating molecular disk orbiting the
young binary star system V4046 Sagittarii. The SMA images provide
an unusually vivid snapshot of the process of formation of giant
planets, comets, and Pluto-like bodies. The results also confirm
that such objects may just as easily form around double stars as
around single stars like our Sun.
These findings are being presented by UCLA graduate student David
Rodriguez in a press conference at the American Astronomical
Society meeting in Pasadena, Calif.
"It's a case of seeing is believing," says Joel Kastner of the
Rochester (NY) Institute of Technology, the lead scientist on the
study. "We had the first evidence for this rotating disk in radio
telescope observations of V4046 Sagittarii that we made last
summer. But at that point, all we had were molecular spectra, and
there are different ways to interpret the spectra. Once we saw the
image data from the SMA, there was no doubt that we have a rotating
disk here."
Co-author David Wilner of the Harvard-Smithsonian Center for
Astrophysics (CfA) adds, "This is strong evidence that planets can
form around binary stars, which expands the number of places we can
look for extrasolar planets. Somewhere in our galaxy, an alien
world may enjoy double sunrises and double sunsets."
Wilner is one of the world's experts on radiointerferometry, the
technique used in this study to form images with the SMA's multiple
radio antennas. The other contributor to the SMA study of V4046
Sagittarii led by RIT's Kastner and UCLA's Rodriguez is Ben
Zuckerman of UCLA.
According to Rodriguez, the images clearly demonstrate that the
molecular disk orbiting the V4046 Sagittarii binary system extends
from within the approximate radius of Neptune's orbit out to about
10 times that orbit. This region corresponds to the zone where the
solar system's giant planets, as well as its Pluto-like Kuiper Belt
objects, may have formed.
"We believe that V4046 Sagittarii provides one of the clearest
examples yet discovered of a Keplerian, planet-forming disk
orbiting a young star system," Wilner says. "This particular system
is made that much more remarkable by the fact that it consists of a
pair of solar-mass stars that are approximately 12 million years
old and are separated by a mere 5 solar diameters."
"This could be the oldest known orbiting protoplanetary molecular
disk. It shows that, at least for some stars, formation of
Jovian-mass planets may continue well after a few million years,
which astronomers have deduced is characteristic of the formation
time for most such planets," Zuckerman says.
Findings of this study build on previous work published in the
December 2008 issue of Astronomy and Astrophysics in which Kastner
and his team first suggested that the case of V4046 Sagittarii
illustrates well how planets may form easily around certain types
of binary stars.
"We thought the molecular gas around these two stars almost
literally represented 'smoking gun' evidence of recent or possibly
ongoing 'giant' Jupiter-like planet formation around the binary
star system," Kastner says. "The SMA images showing an orbiting
disk certainly support that idea."
The evidence for a molecular disk orbiting these twin young suns in
the constellation Sagittarius suggested to the scientists that many
such binary systems should also host as-yet-undetected
planets.
"The most successful technique used so far for the discovery of
extrasolar planets - that of measurement of precision radial
velocities - is exceedingly difficult for close binary stars such
as V4046 Sagittarii. So these radio observations are probing a new
region of discovery space for extrasolar planets," says
Rodriguez.
"At a distance of only 240 light-years from the solar system, the
V4046 Sagittarii binary is at least two times closer to Earth than
almost all known planet-forming star systems, which gives us a good
shot at imaging any planets that have already formed and are now
orbiting the stars," he continues.
Kastner and collaborators had previously used the 30-meter
radiotelescope operated by the Institut de Radio Astronomie
Millimetrique (IRAM) to study radio molecular spectra emitted from
the vicinity of the twin stars. The scientists used these data to
identify the raw materials for planet formation around V4046
Sagittarii - carbon monoxide and hydrogen cyanide - in the noxious
circumstellar gas cloud.
"In this case the stars are so close together, and the profile of
the gas - in terms of the types of molecules that are there - is so
much like the types of gaseous disks that we see around single
stars, that we now have a direct link between planets forming
around single stars and planets forming around double stars,"
Kastner says.
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Harvard-Smithsonian Center for Astrophysics
Thanks to Harvard-Smithsonian Center for Astrophysics for this
article.