Webb observes light scattered by dust in a stellar debris disk

May 30. () –

The James Webb Space Telescope has detected for the first time light scattered by dust grains in the debris disk surrounding the star Fomalhaut C.

As stars and planets form from the collapse of clouds of gas and dust, nascent planetary systems go through a short and poorly understood phase. The disk stage of fleeting debris, that lasts only 10 million years, It is marked by collisions between protoplanets that create disks or rings of dust and debris.

As reported by the American Astronomical Society, the study of debris disks is key to understanding how planetary systems form. Very few debris disks have been observed around the smallest, coldest and most common type of star in the Milky Way (M dwarfs), and detailed observations of the few known debris disks of M dwarfs have been scarce. Studies are divided on whether low-mass stars are less likely to host debris disks or whether these disks are simply harder to detect.

Recent observations with the James Webb Telescope have given researchers new insight into a disk surrounding an M dwarf just 25 light-years away.

Fomalhaut is a three-star system famous for the debris disk and planet candidate around the system’s largest and brightest star, Fomalhaut A. Astronomers previously detected thermal emissions from a debris disk surrounding an M dwarf in the system, Fomalhaut C., in observations made by the Atacama Large Millimeter/submillimeter Array (ALMA), but follow-up observations failed to detect the disk with scattered light. Scattered light observations provide researchers with valuable information about the size and composition of dust grains in the disk.

Recently, a team led by Kellen Lawson (NASA Goddard Space Flight Center) directed James Webb toward Fomalhaut C and eight other nearby M dwarfs to search for planets around these stars. In the telescope’s 3.56 and 4.44 micron (1 micron = 10-6 meters) filters, the authors detected a faint disk extending beyond the star. In the shorter wavelength filter, the disk’s outline matched the location of the debris disk previously seen by ALMA. In the longer wavelength filter, the disk extended slightly beyond the emission seen by ALMA.

Fomalhaut C is the smallest and coolest star for which a disk in scattered light has been detected. The new observations highlight JWST’s ability to track debris disks around small, cool stars, as well as the inherent difficulty of observing these structures: even under JWST’s watchful eye, the star’s debris disk is only faintly visible, with background objects and noise interfering with the telescope’s view.

The study is published in The Astrophysical Journal Letters.