schematic view of the history of the accretion disk and the intruding object

A massive protostellar disk found in the center of the Milky Way

Accretion disks, also known as “protostellar disks”, are key components in star formation. These disks continuously feed gas into protostars from the environment. In this sense, they are star cradles where stars are born and raised.

Recently, a team of astronomers reported the discovery of a massive protostellar disk in The center of the Milky Way. The team also decided how its spiral arms were formed.

The disk has a diameter of about 4,000 astronomical units and surrounds an educational, early O-type star with a mass that is about 32 times that of the Sun.

The discovery was made using high-resolution observational data from the Atacama Large Millimeter / Submillimeter Array (ALMA). The team includes Dr. LU Xing, an assistant researcher at the Shanghai Astronomical Observatory (SHAO) at the Chinese Academy of Sciences, and a fellow at Yunnan University, the Harvard-Smithsonian Center for Astrophysics, and the Max Planck Institute.

According to research, this disc was upset by a close encounter with a nearby object, which caused spiral arms to develop. This discovery suggests that large stars may have originated in the same way as stars with lower masses via accumulators and bypasses.

Using observations from ALMA, the research team achieved a resolution of 40 millisecond seconds. With these high-resolution, high-sensitivity ALMA observations, the team discovered an accretion disk in Galactic Center.

The discovery suggests that early O-type massive stars are undergoing a formation phase involving accumulation disks, and this conclusion is valid for the unique environment of the Galactic Center.

The fascinating thing is that the disc’s two spiral arms are visible. Such arms are usually found in spiral galaxies but rarely in protostellar discs. Spiral alarms in accretion disks are generally formed due to fragmentation induced by gravitational instability.

However, this newly discovered protostellar disk is hot and turbulent, which allows it to balance its gravity.

In an attempt to explain this phenomenon, the researchers suggested an alternative explanation – that the spirals were induced by external disturbances. The researchers suggested this explanation after discovering an object with about three solar masses – possibly the source of the external disturbance – several thousand astronomical units away from the disk.

The team verified this proposal by calculating several dozen possible paths for this object. They found that only one of these tracks could interfere with the disc to the observed level.

They then performed a numerical simulation on the high-performance supercomputer platform of the Shanghai Astronomical Observatory to track the trajectory of the intrusive object. They successfully recounted the entire story of the object that flew past the disk more than 10,000 years ago when it would have stirred spirals in the disk.

Dr LU sa, “The fine matching between analytical calculations, the numerical simulation and the ALMA observations provides robust evidence that the spiral arms in the disk are relics of the intrusion of the penetrating object.”

“This finding shows that accumulation disks in the early evolutionary stages of star formation are subject to frequent dynamic processes such as bypasses, and these processes can significantly affect the formation of stars and planets. “

“The formation of this massive protostar is similar to its lower mass cousins ‚Äč‚Äčlike the Sun, with accretion disks and bypasses involved. Although star masses are different, some physical mechanisms of star formation may be the same. This provides important clues to solving the mystery of massive star formation.”

Journal reference:

  1. Lu, X., Li, GX., Zhang, Q. et al. A massive Keplerian protostellar disk with by-induced helices in the central molecular zone. Nat Astron (2022). DOI: 10.1038 / s41550-022-01681-4


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