ALMA sees icy ring around young Fomalhaut planetary system

Composite image of the Fomalhaut star system. The ALMA data, shown in orange, reveal the distant and eccentric debris disk in never-before-seen detail. The central dot is the unresolved emission from the star, which is about twice the mass of the Sun. Optical data from the Hubble Space Telescope is in blue; the dark region is a coronagraphic mask, which filtered out the otherwise overwhelming light of the central star. Credit: ALMA (ESO/NAOJ/NRAO), M. MacGregor; NASA/ESA Hubble, P. Kalas; B. Saxton (NRAO/AUI/NSF) | Download image

The nearby star of Fomalhaut, which lies at approximately 25 light-years (7.7 pc) in the constellation of Piscis Austrinus has been studied by an international team of astronomers using the Atacama Large Millimetre/submillimeter Array (ALMA) completing the first millimetre-wavelength image of the ring of dusty debris surrounding this young millimetre-wavelength image of the ring of dusty debris surrounding the young main sequence class A star. 

This ring is a remarkably well-defined band of rubble and gas likely to be the result of exocomets smashing together near the outer edges of a planetary system. These observations were able to stablish an analogy to comets in our own Solar System. 

Earlier ALMA observations of Fomalhaut back in 2012 when the telescope was still under construction, revealed only about one half of the debris disk. Though this first image was merely a test of ALMA’s initial capabilities, it nonetheless provided tantalizing hints about the nature and possible origin of the disk.

This new observation of Fomalhaut with ALMA, has provided a stunningly complete view of this glowing band of debris, suggesting that there are chemical similarities between its icy contents and comets in our own solar system.

ALMA image of the debris disk in the Fomalhaut star system. The ring is approximately 20 billion kilometers from the central star and it is about 2 billion kilometers wide. The central dot is the unresolved emission from the star, which is about twice the mass of the Sun. Credit: ALMA (ESO/NAOJ/NRAO); M. MacGregor | Download image

Fomalhaut is a relatively nearby star system and one of only about 20 in which planets have been imaged directly. The entire system is approximately 440 million years old, or about one-tenth the age of our solar system.

Debris disks are common features around young stars and represent a very dynamic and chaotic period in the history of a solar system. Astronomers believe they are formed by the ongoing collisions of comets and other planetesimals in the outer reaches of a recently formed planetary system. The leftover debris from these collisions absorbs light from its central star and reradiates that energy as a faint millimeter-wavelength glow that can be studied with ALMA.

Using the new ALMA data and detailed computer modeling, the researchers could calculate the precise location, width, and geometry of the disk. These parameters confirm that such a narrow ring is likely produced through the gravitational influence of planets in the system. 

Sources: ALMA, Wikipedia.