Formation process of the circumstellar disk: Long-term simulations in the main accretion phase of star formation

Masahiro N. Machida, Shu Ichiro Inutsuka, Tomoaki Matsumoto

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Abstract

The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of ≳3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of ≥3 AU. This means that unmagnetized protoplanetary disk smaller than <3 AU does not exist. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the first core (or the circumstellar disk) has a mass of ∼0.005-0.1 M , while the protostar has a mass of ∼103 M . Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for ∼ 105 yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

Original languageEnglish
Pages (from-to)1006-1020
Number of pages15
JournalAstrophysical Journal
Volume724
Issue number2
DOIs
Publication statusPublished - Dec 1 2010

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protostars
star formation
accretion
simulation
torque
gravitational instability
centrifugal force
protoplanetary disks
fragmentation
molecular clouds
thermodynamics
hydrodynamics
time measurement
signatures
gas
gases

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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Formation process of the circumstellar disk : Long-term simulations in the main accretion phase of star formation. / Machida, Masahiro N.; Inutsuka, Shu Ichiro; Matsumoto, Tomoaki.

In: Astrophysical Journal, Vol. 724, No. 2, 01.12.2010, p. 1006-1020.

Research output: Contribution to journalArticle

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