A team of astronomers has utilized NASA’s James Webb Space Telescope to capture infrared images of the warm dust surrounding Fomalhaut, a nearby young star. Their goal was to study the first asteroid belt ever observed beyond our solar system. However, the astronomers were taken aback by the astonishing complexity of the dusty structures, surpassing the asteroid and Kuiper dust belts within our own solar system.
In total, they identified three nested belts encircling Fomalhaut, extending a remarkable 14 billion miles (23 billion kilometers) from the star—roughly 150 times the distance between Earth and the Sun. The outermost belt’s scale is approximately twice that of our solar system’s Kuiper Belt, which consists of small bodies and cold dust located beyond Neptune. To their amazement, Webb unveiled the presence of previously unseen inner belts, shedding light on these enigmatic features for the first time.
Fomalhaut, known as the brightest star in the southern constellation Piscis Austrinus and visible to the naked eye, is enveloped by these dusty belts, often referred to as “debris disks.” These belts are formed from collisions among larger bodies, akin to asteroids and comets, and bear striking similarities to the components found in our own planetary system. András Gáspár from the University of Arizona, the lead author of the research paper, describes Fomalhaut as the archetype of debris disks discovered elsewhere in our galaxy. By examining the patterns within these rings, scientists can glean insights into the composition of planetary systems and construct a hypothetical framework of how they might appear—if only we had the capability to capture a sufficiently detailed image to observe the suspected planets.
While the Hubble Space Telescope, Herschel Space Observatory, and the Atacama Large Millimeter/submillimeter Array (ALMA) have previously obtained clear images of the outermost belt, none of them had detected any internal structures. For the first time, Webb’s infrared observations resolved the presence of inner belts, surpassing the capabilities of its predecessors. Schuyler Wolff, another member of the University of Arizona team, explains that Webb’s advantage lies in its ability to physically capture the thermal glow emitted by dust in these inner regions, thus unveiling belts that were previously hidden from view.
By combining data from Hubble, ALMA, and Webb, astronomers are working collaboratively to assemble a comprehensive understanding of debris disks around various stars. Wolff explains that while Hubble and ALMA have provided valuable insights into the formation and evolution of outer disks by imaging multiple analogs of the Kuiper Belt, Webb’s capabilities will enable the observation of a dozen or more asteroid belts in different star systems. This will yield equally significant knowledge about the warm inner regions of these disks, akin to what Hubble and ALMA have taught us about the colder outer regions.
The formation of these belts is most likely influenced by the gravitational forces exerted by unseen planets. In our own solar system, for instance, Jupiter acts as a shepherd for the asteroid belt, while Neptune sculpts the inner edge of the Kuiper Belt. Similarly, there may be undiscovered celestial bodies beyond the Kuiper Belt that play a role in shaping its outer edge. As Webb continues to capture images of additional star systems, scientists anticipate unraveling further insights into the planetary configurations within these systems.
The presence of Fomalhaut’s dust ring was initially detected in 1983 through observations made by NASA’s Infrared Astronomical Satellite (IRAS). Further evidence of the ring’s existence has been inferred from previous observations using submillimeter telescopes on Mauna Kea, Hawaii, NASA’s Spitzer Space Telescope, and Caltech’s Submillimeter Observatory.
George Rieke, the U.S. science lead for Webb’s Mid-Infrared Instrument (MIRI) and a member of the team, describes the belts surrounding Fomalhaut as a captivating mystery, questioning the whereabouts of the planets. He believes that the star likely hosts an intriguing planetary system.
The unexpected complexity of the structure, including the presence of a second intermediate belt and a broader asteroid belt, has aroused excitement among the researchers. Such features often prompt astronomers to speculate about the possibility of embedded planets influencing the formation of these rings.
Webb’s observations also captured what the team refers to as “the great dust cloud,” potentially indicating a collision between two protoplanetary bodies within the outer ring. This feature differs from a suspected planet initially observed inside the outer ring by Hubble in 2008. Subsequent Hubble observations revealed that the object had disappeared by 2014. A plausible explanation is that this newly discovered feature, similar to its predecessor, is an expanding cloud of extremely fine dust particles resulting from a collision between two icy bodies.
The concept of a protoplanetary disk surrounding a star traces back to the late 1700s, when astronomers Immanuel Kant and Pierre-Simon Laplace independently developed a theory suggesting that the Sun and planets formed from a rotating gas cloud that collapsed and flattened under the influence of gravity. Debris disks emerge later in the process, following the formation of planets and the dissipation of the original gas in the system. These disks provide valuable insights as they reveal that small celestial bodies like asteroids collide catastrophically, generating vast clouds of dust and debris. By studying the dust within these disks, astronomers gain unique clues about the structure of exoplanetary systems, enabling investigations into objects as small as Earth-sized planets and asteroids, which are individually too tiny to observe.
The team’s findings are set to be published in the journal Nature Astronomy.