April 12, 2012
Astronomers Use ALMA To Dissect Nearby Planetary System
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Astronomers have made a breakthrough discovery in understanding a nearby planetary system, giving clues about how these systems form and evolve.
Scientists used the Atacama Large Millimeter/submillimeter Array (ALMA) to find that planets orbiting the star Fomalhaut must be smaller than originally thought.
The high-resolution images show that both the inner and outer edges of the thin, dusty disk have very sharp edges. This, as well as computer simulations, have led the astronomers to believe that the dust particles in the disk are kept within the disk by the gravitational effect of two planets.
The team also found that the probable size of the planets is that they are larger than Mars but no larger than a few times the size of the Earth.
"Combining ALMA observations of the ring's shape with computer models, we can place very tight limits on the mass and orbit of any planet near the ring," Aaron Boley, a Sagan Fellow at the University of Florida, leader of the study, said in a press release "The masses of these planets must be small; otherwise the planets would destroy the ring."
The sizes of the planets help explain why earlier infrared observations failed to detect the planets, despite an image by the Hubble Space Telescope (HST) revealing the inner planet.
The ALMA observations traced larger dust grains that are not moved by the star's radiation. This helped the astronomers clearly see the disk's sharp edges, indicating the gravitational effect of the two planets.
The ring is about 16 times the distance from the Sun to the Earth, and is only one-seventh as thick as it is wide.
"The ring is even more narrow and thinner than previously thought," Matthew Payne, also of the University of Florida, said in a press release.
Only a quarter of ALMA's planned 66 antennas were available during the astronomer's observations. Once construction is completed next year, the full system will be better equipped for research.
"ALMA may be still under construction, but it is already the most powerful telescope of its kind," ESO astronomer and team member Bill Dent said in a press release. "This is just the beginning of an exciting new era in the study of discs and planet formation around other stars."
The astronomers will be publishing their research in Astrophysical Journal Letters.
Image 1: This view shows a new picture of the dust ring around the bright star Fomalhaut from the Atacama Large Millimeter/submillimeter Array (ALMA). The underlying blue picture shows an earlier picture obtained by the NASA/ESA Hubble Space Telescope. The new ALMA image has given astronomers a major breakthrough in understanding a nearby planetary system and provided valuable clues about how such systems form and evolve. Note that ALMA has so far only observed a part of the ring. Credit: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope. Acknowledgement: A.C. Boley (University of Florida, Sagan Fellow), M.J. Payne, E.B. Ford, M. Shabran (University of Florida), S. Corder (North American ALMA Science Center, National Radio Astronomy Observatory), and W. Dent (ALMA, Chile), P. Kalas, J. Graham, E. Chiang, E. Kite (University of California, Berkeley), M. Clampin (NASA Goddard Space Flight Center), M. Fitzgerald (Lawrence Livermore National Laboratory), and K. Stapelfeldt and J. Krist (NASA Jet Propulsion Laboratory)
Image 2: This chart shows the location of the bright star Fomalhaut in the constellation of Piscis Austrinus (The Southern Fish). This map shows most of the stars visible to the unaided eye under good conditions. Fomalhaut is the brightest star in the constellation and one of the brightest stars known to have an orbiting planet. It lies about 25 light-years from the Earth and is surrounded by a huge disc of dust. Credit: ESO, IAU and Sky & Telescope