Century-old stellar mystery may have explanation

Astronomers may have finally solved a century-old stellar mystery involving the star FU Orionis, which suddenly brightened dramatically in 1936 and has remained unusually luminous ever since. New research suggests that the outburst was caused by the star devouring a massive amount of gas from a surrounding disk, rather than a more exotic event like a stellar merger. The findings, published in The Astrophysical Journal, provide a long-sought explanation for the star's strange behavior.

The star FU Orionis, located about 1,500 light-years away in the constellation Orion, is the namesake of a class of young stellar objects known as FU Orionis stars. These stars undergo sudden, extreme increases in brightness—up to 100 times or more—that can last for decades or centuries. FU Orionis itself brightened by a factor of 250 in 1936 and has stayed bright ever since, puzzling astronomers who have debated the cause for nearly 90 years.

The new study, led by researchers at the University of Texas at Austin, used observations from the Stratospheric Observatory for Infrared Astronomy (SOFIA) and the Hubble Space Telescope to analyze the star's light. They found that the outburst was likely triggered by a sudden influx of gas from the star's protoplanetary disk, which heated the star's surface and caused it to expand and brighten. This process, known as accretion, is common in young stars but usually occurs at a much slower rate.

The discovery matters because it helps explain the evolution of young stars and their planetary systems. FU Orionis outbursts may be a normal phase in the life of many Sun-like stars, potentially affecting the formation of planets around them. The intense radiation and heat from such an event could alter the chemistry of the surrounding disk, influencing the types of planets that form.

According to the researchers, the next step is to study other FU Orionis stars to see if they share similar properties. This could confirm whether accretion-driven outbursts are a universal phenomenon in young stellar evolution. The findings also highlight the importance of continued observations of these enigmatic stars to fully understand their behavior and impact on planet formation.