Stars are born in the midst of large clouds of gas and dust. Local condensations initially form "embryos", which then collect and grow matter. But how exactly does this accretion process work? And what happens when two stars form in a disk of matter? High-resolution images of a young star-binary system reveal, for the first time, a complex network of accretion filaments that form two protostars in the center of the circumbinary disk. With these observations, an international team of astronomers, led by the Max Planck Institute for Extraterrestrial Physics, succeeded in identifying a two-stage accretion process that causes the formation and evolution of binary star systems.
Most stars in the universe occur in the form of pairs – binaries – or even multi-star systems. The formation of such a binary star system has now been observed for the first time with high-resolution ALMA images (Atacama Large Millimeter / Submillimeter Array). An international team of astronomers led by the Max Planck Institute for Extraterrestrial Physics aimed at the system [BHB2007] 11, the youngest member of a small group of young star objects in the Barnard 59 nucleus in the molecular cloud of the Pipe Nebula. While previous observations showed an accretion envelope surrounding a circumbinary disk, the new observations now reveal their internal structure as well.
"We see two compact sources, which we interpret as circumstellar disks around the two young stars," explains Felipe Alves of the MPE, who led the study. "The size of each of these disks is similar to the asteroid belt in our solar system, and their mutual distance is about twenty-eight times the distance between Earth and the Sun." Both protostars are surrounded by a circular disk with a total mass of about 80 Jupiter masses, which shows a complex network of spirally distributed dust structures. The shape of the filaments suggests streamer-incident material, which is confirmed by the observation of molecular emission lines.
"This is a really important result," says Paola Caselli, director and MPE and director of the Center for Astrochemical Studies. "We have finally mapped the complex structure of young binary stars, whose 'feeding filaments' connect them to the circumbinary disk, which presents important limitations to current models of star formation."
The astronomers interpret the filaments as inflows of the extended circumbinary disk, where the circumstellar disk receives more input around the less massive of the two protostars, which agrees with the theoretical predictions. The estimated accretion rate is only about 0.01 Jupiter mass per year, which is consistent with the rates estimated for other protostellar systems. Just like the orbiting disk feeding the circumstellar disks, each circumstellar disk feeds the protosters in its center. At the disk star level, however, the accretion rate derived from the observations is higher for the more massive object. The observation of the emission of an extended radio beam for the northern object confirms this result. This is an independent indication that these protostars actually enrich more material.
System during its mass accretion phase, "says Alves," Although the good agreement of these observations with the theory is already very promising, we need to study more recent binary systems in detail to further constrain the conditions that lead to star multiplication. "
Massive stars grow just like bright stars, only bigger ones
F.O. Alves el al., Gas Flow and Accretion via Spiral Streamer and Circumstellar Disks in a Young Double Star, Science (2019). science.sciencemag.org/cgi/doi… 1126 / science.aaw3491
Astronomers observe how two suns collect matter in a binary system (2019, October 4)
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