Fomalhaut, the 18th brightest star visible in the night sky, is orbited by the compact light source Fomalhaut b, which has been previously interpreted as either a dusty exoplanet or debris from a collision of two planetesimals. While such collisions are seldom witnessed, their remnants can be captured in images. Recent observations from the NASA/ESA Hubble Space Telescope indicate that a second point source is expected to appear around Fomalhaut in 2023, reminiscent of Fomalhaut b’s appearance two decades ago. Astronomer Paul Karas from the University of California, Berkeley, and his team suggest this new source is a dust cloud resulting from a recent collision between two planetesimals.
This Hubble image shows the debris ring and dust clouds CS1 and CS2 around Fomalhaut. Image credit: NASA / ESA / P. Kalas, University of California, Berkeley / J. DePasquale, STScI.
Fomalhaut is an A-type star located a mere 25 light-years away in the constellation Austrinus Pisces.
The name Fomalhaut originates from its Arabic name, Hum Al Hat, which translates to “fish mouth.”
This star is twice as massive and 20 times more luminous than the Sun, encircled by a ring of dust and debris.
In 2008, astronomers utilized Hubble to identify a potential planet surrounding Fomalhaut, marking it as the first star system where a potential planet was detected using visible light.
The object termed Fomalhaut b presently resembles a dust cloud that appears akin to a planet, resulting from a planetesimal impact.
During new Hubble observations aimed at locating Fomalhaut b, Dr. Karas and his colleagues were astonished to discover a second point of light positioned similarly around the star.
This new object has been dubbed Stellar Frequency Source 2 (cs2), while the original object is now referred to as cs1.
“This is definitely the first instance we’ve observed a point of light spontaneously appearing in an exoplanetary system,” remarked Dr. Karas.
“Hubble images up to now have not shown this. What we’re witnessing is a violent collision between two massive bodies creating an enormous debris cloud, unlike anything else currently seen in our solar system. It’s incredible.”
The proximity of these two debris clouds remains a puzzle for astronomers.
If asteroid and planetesimal collisions were random, cs1 and cs2 should ideally be found in unrelated positions.
However, they are intriguingly located close together along the inner edge of Fomalhaut’s outer debris disk.
Another enigma is the occurrence of these two events in such a brief timespan.
“Previous theories indicated that impacts should occur roughly once every 100,000 years or more. Yet, we’ve observed two impacts in just 20 years,” Dr. Karas noted.
“If you had movies from the past 3,000 years and fast-forwarded them to make a year just a fraction of a second, imagine how many flashes you’d see during that period.”
“The Fomalhaut planetary system will continue to provide insights into these collisions.”
Collisions are crucial for the evolution of planetary systems, yet they are infrequent and challenging to study.
Dr. Mark Wyatt, an astronomer at the University of Cambridge, stated: “The intrigue of this observation lies in its ability to assist researchers in estimating the size of the impactor and the number of objects present in the disk. This data is nearly impossible to obtain through other methods.”
“We estimate that the planetesimals destroyed to form CS1 and CS2 were only around 30 km in diameter, suggesting there are approximately 300 million such objects orbiting the Fomalhaut system.”
“This system effectively serves as a natural laboratory for studying the behavior of planetesimals during collisions, enabling us to learn about their composition and formation.”
For further details, see this result. Featured in this week’s Science diary.
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Paul Kalas and colleagues. 2025. Second planetesimal impact in the Fomalhaut system. Science published online on December 18, 2025. doi: 10.1126/science.adu6266
Source: www.sci.news
