Each star in the universe begins inside a rotating cloud of gas and dust that contracts to stellar densities due to the force of its own gravity. However, before these clouds harbor stars, the vast majority of them land onto a circumstellar disk that formed around the star due to the conservation of angular momentum. The process by which the cloud makes its way through the disk and onto the star, which leads to an increase in the star's mass, is the focus of many current astrophysical studies.
While it was previously believed that the star's final mass is the result of a steady accumulation, a new study by researchers from the University of Vienna suggests that this is not the case. Instead, the study reveals that the final mass is likely due to a series of violent events characterized by stellar brightening. One example of this can be seen in the young FU Orionis star located in the Orion constellation, which increased in brightness by a factor of 250 over just one year and has remained in this state for almost 100 years.
The new theory outlined in the current study proposes that this stellar brightening is caused by fragmentation that stems from gravitational instability in the gaseous disks that surround early stars. Subsequently, dense clumps of gas make their way onto the star. During the process of this transfer of gaseous clumps, excess energy is released that causes the brightening of the young star by huge factors - up to hundreds of thousands.
Eduard Vorobyov, co-author of the study, believes that this process can be described as "cannibalism on astronomical scales" and will further our understanding of the formation of planets and stars.
"This is a major step towards our understanding of how stars and planets form and evolve," he said in a press release. "If we can prove that most stars undergo such episodes of brightening caused by disk gravitational instability, this would mean that our own sun might have experienced several such episodes, implying that the giant planets of the solar system may in fact be lucky survivors of the sun's tempestuous past."
The findings were published in the Feb. 5 issue of Science Advances.
