The finer details of how fledgling stars form is shrouded in mystery and, more literally, dust. By using one of the world’s most advanced observatories, however, the mystery is clearing and the dust is coming into focus. And it appears to be shaped like a pretzel.
Two baby stars were discovered in the [BHB2007] 11 system located between 600 and 700 light-years from Earth. Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers were able to study the distribution of dust around these two stars with incredibly high precision, focusing on the dust both near and far from the objects, publishing their findings in Science.
The twin stars are surrounded by stellar disks, each weighing a few times the mass of Jupiter and extending for less than 500 million kilometers (300 million miles). These circumstellar disks are key for stellar evolution, as stars grow by feeding on the material they can steal from them.
“We see two compact sources that we interpret as circumstellar disks around the two young stars,” lead author Felipe Alves from the Max Planck Institute for Extraterrestrial Physics, said in a statement. “The size of each of these disks is similar to the asteroid belt in our Solar System and the separation between them is 28 times the distance between the Sun and the Earth.”
The "cosmic pretzel" is shaped by the gravitational and electromagnetic forces of the system, and has a mass of roughly 80 Jupiters. The visually striking pretzel-like appearance is actually a complex interlaced stream of dust that surrounds the entire system, and the spiral structures provide details on how the dust feeds onto the stars. The process is not direct; the stars accrete mass from the disk in two stages. The material in the disk is accreted into the stellar disk, in the loops seen imaged by ALMA, and then the stars accrete the material from their circumstellar disks. Data analysis of the image also shows the less massive, brighter circumstellar disk (the lower one in the image) accretes more material.
“We expect this two-level accretion process to drive the dynamics of the binary system during its mass accretion phase,” said Alves. “While the good agreement of these observations with theory is already very promising, we will need to study more young binary systems in detail to better understand how multiple stars form.”
These observations are very important. There are still many unknowns on how stars form and these observations put specific constraints on the model we use in stellar astronomy.