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Over the past several years, the Atacama Large Millimeter/submillimeter Array (ALMA) has transformed our understanding of protoplanetary disks -- the gas- and dust-filled planet factories that encircle young stars. The rings and gaps in these disks provide intriguing circumstantial evidence for the presence of planets. Other phenomena, however, could account for these tantalizing features.
Using a new planet-hunting technique that identifies unusual patterns in the flow of gas within a protoplanetary disk, two teams of astronomers have confirmed the distinct, telltale hallmarks of newly formed planets orbiting an infant star in our galaxy. These results are presented in a pair of papers appearing in the Astrophysical Journal Letters.
Motion - Gas - Star - Disk - Approach
"We looked at the localized, small-scale motion of gas in a star's protoplanetary disk. This entirely new approach could uncover some of the youngest planets in our galaxy, all thanks to the high-resolution images coming from ALMA," said Richard Teague, an astronomer at the University of Michigan and principal author on one of the papers.
To make their respective discoveries, each team analyzed the data from various ALMA observations of the young star HD 163296. HD 163296 is about 4 million years old and located about 330 light-years from Earth in the direction of the constellation Sagittarius.
Dust - Disk - ALMA - Observation - Astronomers
Rather than focusing on the dust within the disk, which was clearly imaged in earlier ALMA observation, the astronomers instead studied the distribution and motion of carbon monoxide (CO) gas throughout the disk. Molecules of CO naturally emit a very distinctive millimeter-wavelength light that ALMA can observe. Subtle changes in the wavelength of this light due to the Doppler effect provide a glimpse into the kinematics -- or motion -- of the gas in the disk.
If there were no planets, gas would move around a star in a very simple, predictable pattern known as Keplerian rotation.
"It would take a...
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