'Cannibalism' between stars
One possible mechanism that can explain these brightening events was put forward 10 years ago by Eduard Vorobyov, now working at the Astrophysical Department of the Vienna University, in collaboration with Shantanu Basu from the University of Western Ontario, Canada.
According to their theory, stellar brightening can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Like the process of throwing logs into a fireplace, these episodes of clump consumption release excess energy which causes the young star to brighten by a factor of hundreds to thousands. During each episode, the star is consuming the equivalent of one Earth mass every ten days. After this, it may take another several thousand years before another event occurs.
With the advent of advanced observational instruments, such as SUBARU 8.2 meter optical-infrared telescope installed in Mauna Kea (Hawaii), it has become possible for the first time to test the model predictions. Using high-resolution, adaptive optics observations in the polarized light, an international group of astronomers led by Hauyu Liu from European Space Observatory (Garching, Germany) has verified the presence of the key features associated with the disk fragmentation model -- large-scale arms and arcs surrounding four young stars undergoing luminous outbursts, including the prototype FU Orionis star itself. The results of this study were accepted for publication in Science Advances -- a peer-review, open-access journal belonging to the Science publishing group.
"This is a major step towards our understanding of how stars and planets form and evolve," says Vorobyov, "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."
Source: University of Vienna [February 05, 2016]