Young star systems are a place of violent collisions. Rocks, comets, asteroids and larger objects carom off one another and coalesce, gradually turning the primordial dust and ice of a stellar nebula into planets and moons. The largest of these collisions, however, are expected to be rare over the hundreds of millions of years it takes to form a planetary system — perhaps one every 100,000 years.
Now, astronomers have seen the aftermath of two powerful collisions within a 20-year period around a nearby star called Fomalhaut. These are either lucky observations or a sign that collisions are more frequent than predicted during planet formation.
The events — the first was detected in 2004 and the second in 2023 — are the first collisions between large objects directly imaged in any solar system outside our own.
“We just witnessed the collision of two planetesimals and the dust cloud that gets spewed out of that violent event, which begins reflecting light from the host star,” said Paul Kalas, adjunct professor of astronomy at the University of California, Berkeley, and first author of the report. “We do not directly see the two objects that crashed into each other, but we can spot the aftermath of this enormous impact.”
Over tens of thousands of years, he said, the dust around Fomalhaut would be “sparkling with these collisions” — like twinkling holiday lights.