ASIAA: Youngest Accretion Disk Detected in Star Formation

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ASIAA: Youngest Accretion Disk Detected in Star Formation

Post by bystander » Tue Sep 04, 2018 6:44 pm

Youngest Accretion Disk Detected in Star Formation
Academia Sinica Institute of Astronomy and Astrophysics | 2018 Sep 04

In Support of an “Early-Start, Slow-Growth” Scenario for Accretion Disk Formation

hh211.png
Disk and outflow in the HH 211 protostellar system. A zoom-in to the innermost region
around the central protostar, showing the disk and outflow there. Asterisk marks the
possible position of the central protostar. Gray arrows show the jet axis. Orange image
shows the dusty disk at submillimeter wavelength obtained with ALMA. Blue and red
images show the blueshifted and redshifted parts of the outflow coming out from the
disk rotating around the jet axis. Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al

An international team led by Chin-Fei Lee at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has discovered a very small accretion disk formed around one of the youngest protostars, with the Atacama Large Millimeter/submillimeter Array (ALMA). This discovery poses a constraint on current theory of disk formation stronger than before, by pushing the disk formation time by a factor of a few earlier. Moreover, a compact rotating outflow has been detected. It may trace a disk wind carrying away angular momentum from the disk and thus facilitate the disk formation.

“ALMA is so powerful that it can resolve an accretion disk with a radius as small as 15 astronomical units (AU),” says Chin-Fei Lee at ASIAA. “Since this disk is about a few times younger than the previously resolved youngest disk, our result has provided a stronger constraint on current theory of disk formation by pushing the disk formation time by a factor of a few earlier. Moreover, together with the previous results of the older disks, our disk result favors a model where the disk radius grows linearly with the protostellar mass, and thus supporting the ‘early-start, slow-growth’ scenario against the ‘slow-start, rapid-growth’ scenario for accretion disk formation around protostars.”

HH 211 is one of the youngest protostellar systems in Perseus at a distance of about 770 light-years. The central protostar has an age of only about 10,000 years (which is about 2 millionths of the age of our Sun) and a mass of less than 0.05 solar mass. It drives a powerful bipolar jet and thus must accrete material efficiently. ...

ALMA Observations of the Very Young Class 0 Protostellar System
HH211-mms: A 30 au Dusty Disk with a Disk Wind Traced by SO?
~ Chin-Fei Lee et al
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ASIAA: Magnetic Fields Found in Jet from Baby Star

Post by bystander » Thu Nov 29, 2018 5:58 pm

Magnetic Fields Found in Jet from Baby Star
Academia Sinica Institute of Astronomy and Astrophysics | 2018 Nov 29
Click to play embedded YouTube video.
Magnetic fields found in a Jet from a Baby Star
Image Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al.
Video editor: ASIAA/Lauren Huang

An international research team led by Chin-Fei Lee in the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has made a breakthrough observation with the Atacama Large Millimeter/submillimeter Array (ALMA), confirming the presence of magnetic fields in a jet from a protostar (baby star). Jet is believed to play an important role in star formation, enabling the protostar to accrete mass from an accretion disk by carrying away angular momentum from the disk. It is highly supersonic and collimated, and predicted in theory to be launched and collimated by magnetic fields. The finding supports the theoretical prediction and confirms the role of the jet in star formation.

“Although it has been long predicted that protostellar jet is threaded with magnetic fields, no one is really sure about it. Thanks to the high-sensitivity of ALMA, we have finally confirmed the presence of magnetic fields in a protostellar jet with molecular line polarization detection. More interestingly, the magnetic fields in the jet could be helical, as seen in the jet from an active galactic nucleus (AGN). Perhaps, the same mechanism is at work to launch and collimate the jets from both protostar and AGN,” says Chin-Fei Lee at ASIAA.

“The detected polarization comes from a SiO molecular line in the presence of magnetic fields,” says Hsiang-Chih Hwang, who was a former NTU undergraduate student of Chin-Fei Lee modeling the polarization. “The polarized emission in the jet is so faint that we failed to detect it with Submillimeter Array. We are so excited to have finally detected it with ALMA.”

HH 211 is a well-defined jet from one of the youngest protostellar systems in Perseus at a distance of about 1,000 light-years. The central powering protostar has an age of only about 10,000 years (which is about 2 millionths of the age of our Sun) and a mass of about 0.05 solar mass. The jet is rich in SiO molecular gas and drives a spectacular molecular outflow around it ...

Unveiling a Magnetized Jet from a Low-Mass Protostar ~ Chin-Fei Lee et al
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