The Orion Nebula Age Paradox

Leiden astronomers propose stellar collision as explanation for Orion Nebula's age paradox

November 5, 2026 | Leiden Convention Bureau | |

Astronomers from Leiden University and collaborating institutions have proposed a new explanation for a longstanding mystery surrounding the Orion Nebula. Although its stars are approximately one million years old, the surrounding gas structures and planet-forming discs appear considerably younger. New research suggests that a collision between two stars around 200,000 years ago could explain this apparent contradiction.

The Orion Nebula

The Orion Nebula is a vast star-forming region visible to the naked eye. Several young stars are surrounded by discs of gas and dust where planets may eventually develop. These discs are gradually eroded by intense radiation from the massive central star, Theta-1 Orionis C1. Given the age of the stars, the discs should have disappeared long ago. Meanwhile, the expanding gas shell surrounding the central star also appears to be only a few hundred thousand years old.

Leiden astronomer Maite Wilhelm and her colleagues investigated whether a stellar collision could account for these observations. Their hypothesis suggests that the central star, approximately 33.5 times the mass of the Sun, formed through the merger of two stars in a binary system. A third star may have disrupted their orbits, ultimately causing them to collide. The researchers used computer simulations to explore how such an event would have affected the surrounding nebula.

Their simulations support this scenario. Before the merger, the two separate stars emitted considerably less radiation, allowing the planet-forming discs to survive for much longer. Following the collision, the resulting increase in radiation accelerated their evaporation. The researchers also suggest that gas released from these discs could help explain the rapid expansion of the surrounding gas shell. The proposed merger offers additional explanations for the central star's tilted magnetic field and slightly elevated nitrogen levels.

According to co-author Simon Portegies Zwart, the findings suggest that stellar collisions may be more common than previously thought. The study highlights how interactions within multiple-star systems can profoundly influence their surroundings, potentially even affecting planets that are still forming. By connecting these processes, the research provides a new perspective on the evolution of the Orion Nebula and the wider consequences of stellar collisions.