Dust ring around the star Fomalhaut is seen by ALMA

Astronomers using the new still under construction observatory Atacama Large Millimeter/submillimeter Array (ALMA), have discovered that planets orbiting the star Fomalhaut must be much smaller than originally thought. This is the first published science result from ALMA in its first period of open observations.

Image above: The underlying blue picture, of the dust ring around the bright star Fomalhaut from ALMA, 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.  Image credit: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope



This discovery has given astronomers a major breakthrough in understanding a nearby planetary system and provided valuable clues about how such systems form and evolve.

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,” said Aaron Boley (a Sagan Fellow at the University of Florida, USA) who was leader of the study. “The masses of these planets must be small; otherwise the planets would destroy the ring,” he added. The small sizes of the planets explain why the earlier infrared observations failed to detect them, the scientists said.

Dust ring around the star Fomalhaut is seen by ALMA

Particles in the dust ring are kept inside the ring by gravitational interactions with planets. The faster-moving inner planet transfers energy to dust particles, moving them outward, deeper into the ring. The slower-moving outer planet removes energy from the particles, causing them to drop inward.  Image credit: ALMA (ESO/NAOJ/NRAO)/B. Saxton



star Fomalhaut in the sky map

via ESO