Astronomers from the Center for Astrophysics | Harvard & Smithsonian and Johns Hopkins University have made the highest-resolution image to date of the warped disk surrounding one of the brightest and most well-studied stars in our cosmic neighborhood.
The new debris disk image was created with the Atacama Large Millimeter/submillimeter Array (ALMA) telescope and helped the scientists understand why the star, called Fomalhaut, has unusual and mysterious architecture.
The image reveals that the distance from the star predicts the disk’s lopsidedness, or eccentricity, and may be influenced by a hidden planet.
“Our observations show, for the first time, that the disk’s eccentricity isn’t constant,” said astrophysicist Joshua Bennett Lovell, a Submillimeter Array Fellow with CfA. “It steadily drops off with distance, a finding that has never before been conclusively demonstrated in any debris disk.”
Lovell and the research team published two papers analyzing these new observations in the Astrophysical Journal and Astrophysical Journal Letters.
Debris disks are vast belts of dust and rocky bodies surrounding a star, similar to but larger than our solar system’s asteroid belt. Fomalhaut’s disk is unusual because it’s not symmetrical, but warped. This phenomenon has fascinated scientists for nearly two decades.
Unlike previous models assuming a uniform or “fixed” eccentricity, their new data-driven model shows that the disk’s shape grows less stretched the farther a segment is from Fomalhaut. The relationship is as if Saturn was a star and wasn’t exactly in the middle of its rings.
Using high-resolution ALMA images at 1.3mm wavelengths, the team fitted a new model to the data that accounts for the disk’s radius, width, and asymmetries, and can alter its eccentricity with distance from the star. The best-fitting model pointed to a steep decline in eccentricity with distance, which has been predicted by theories of how planets can shape debris disks, but hasn’t yet been seen anywhere in the universe.
This negative gradient offers clues about possible hidden planets orbiting Fomalhaut. The new model suggests a massive planet orbiting inside of Fomalhaut’s disk may have sculpted its eccentricity profile early in that solar system’s history. The unusual shape may have developed in the system’s youth and the continued push and pull of this planet may have kept the disk this way for more than 400 million years.
The second paper ruled out the possibility that the ring’s eccentricity is fixed with distance from the star.
“Although the shift in brightness was expected, the precise shifts that we measured in the disk brightness and the ring’s width could not be explained by the old models,” said graduate student Jay Chittidi of Johns Hopkins University.
“Simply put: we couldn’t find a model with a fixed eccentricity that could explain these peculiar features in Fomalhaut’s disk. Comparing the old and new models, we are now able to better interpret this disk, and reconstruct the history and present state of this dynamic system.”
Researchers hope this new model will be further tested with future approved ALMA observations.
“And hopefully we’ll find new clues that will help us uncover that planet,” added Lovell.
The team has shared the eccentricity model code developed for this newly published research to enable other astronomers to apply it to similar systems.
The Center for Astrophysics | Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask—and ultimately answer—humanity's greatest unresolved questions about the nature of the universe. The Center for Astrophysics is headquartered in Cambridge, MA, with research facilities across the U.S. and around the world.
The National Radio Astronomy Observatory (NRAO) is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
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Christine Buckley Director of Communications Center for Astrophysics | Harvard & Smithsonian
