How do mysterious free-floating planetary-mass objects form without stars? A new study explains

A team of astronomers has uncovered fresh insights into free-floating planetary-mass objects (PMOs), strange celestial bodies wandering through space without a host star. Using advanced simulations, researchers have proposed a new theory explaining how these cosmic drifters may form.

A New Theory on PMO Formation
PMOs, often found in young star clusters like Orion’s Trapezium, have puzzled scientists for years. These objects, with masses below 13 times that of Jupiter, were previously thought to be failed stars or ejected planets. However, these theories could not explain the high number of PMOs, their frequent binary pairings, or their coordinated movement with stars.

Led by Dr Deng Hongping of the Shanghai Astronomical Observatory, an international team used high-resolution simulations to model interactions between circumstellar disks—rings of gas and dust around young stars. Their study, published in Science Advances, suggests that PMOs can form when these disks collide in dense star clusters.

How Disks Collide to Create PMOs
The simulations showed that when two circumstellar disks pass within 300–400 astronomical units (AU) of each other, gravitational forces create elongated "tidal bridges" of gas. These bridges collapse into dense filaments, which then fragment into compact cores. When these filaments gain enough mass, they form PMOs roughly ten times the mass of Jupiter.