Free Astronomy Magazine November-December 2025

NOVEMBER-DECEMBER 2025 T his view shows a new picture of the dust ring around the bright star Fomal- haut from the Atacama Large Millimeter/submillimeter Array (ALMA). The un- derlying blue picture shows an earlier picture obtained by the NASA/ESA Hubble Space Telescope. [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. Fitzger- ald (Lawrence Livermore National Laboratory), and K. Stapelfeldt and J. Krist (NASA Jet Propulsion Laboratory)] resolution ALMA images at 1.3mm wavelengths, the team fitted a new model setup to the data, one that accounts for the disk’s radius, width, and asymmetries, with an eccentric ring model that can alter its eccen- tricity with distance from the star. The best-fitting model pointed to a steep decline in eccentricity with distance, as predicted by dynamical theories of how planets can shape debris disks, but as-yet seen any- where in the universe. This negative gradient offers clues about hidden planets, currently un- seen by astronomers, orbiting Fo- malhaut. The new model suggests a massive planet orbiting inside of Fo- malhaut’s disk may have sculpted its eccentricity profile early in the ex- trasolar system’s history. The un- usual shape of the debris disk may have formed in the system’s youth, during the protoplanetary disk phase, and has remained this way for more than 400 million years, thanks to the continued push, and pull of this planet. In the second paper, led by Gradu- ate Student Jay Chittidi at Johns Hopkins University, the team ex- hausted the possibility that the ring’s eccentricity is fixed with the distance from the star. “Although the shift in brightness from the pericenter side of the disk, nearest to the star, to the apocenter side, furthest from the star, be- tween the JWST and ALMA data 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 Jay. “Simply put: we couldn’t find a model with a fixed eccentricity that could explain these peculiar fea- tures in Fomalhaut’s disk. Compar- ing the old and new models, we are now able to better interpret this disk, and reconstruct the history and present state of this dynamic sys- tem.” Researchers hope this new model will be further tested with more ALMA observations, which were recently approved, “And hopefully we’ll find new clues that will help us uncover that planet!” adds Lovell. The team has shared the eccentricity model code devel- oped for this research to enable other astronomers to apply it to similar systems. !